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Technical  and  Bibliographic  Notes/Notes  techniques  et  bibliographiques 


The  Institute  has  attempted  to  obtain  the  best 
original  copy  available  for  filming.  Features  of  this 
copy  which  may  be  bibliographically  unique, 
which  may  alter  any  of  the  images  in  the 
reproduction,  or  which  may  significantly  change 
the  usual  method  of  filming,  are  checked  below. 


□    Coloured  covers/ 
Couverture  de  couleur 


I — I    Covers  damaged/ 


Couverture  endommagie 


□    Covers  restored  and/or  laminated/ 
Couverture  restaur6e  et/ou  pelliculie 

I — I    Cover  title  missing/ 


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Le  titre  de  couverture  manque 

Coloured  maps/ 

Cartes  gdographiques  en  couleur 

Coloured  ink  (i.e.  other  than  b!ue  or  black)/ 
Encre  de  couleur  (i.e.  autre  que  bleue  ou  noirei 

Coloured  plates  and/or  illustrations/ 
Planches  et/ou  illustrations  en  couleur 

Bound  with  other  material/ 
Relii  avec  d'a^tres  documents 

Tight  binding  may  cause  shadows  or  distortion 
along  interior  margin/ 

Lareliure  serr^e  peut  causer  de  I'ombre  ou  de  la 
distortion  le  long  de  la  marge  intArieure 

Blank  leaves  added  during  restoration  may 
appear  within  the  text.  Whenever  possible,  these 
have  been  omitted  from  filming/ 
II  se  peut  que  certaines  pages  blanches  ajouties 
lors  dune  rsstauration  apparaissent  dans  le  texte, 
mais,  lorsque  cela  Atait  possible,  ces  pages  n'ont 
pas  M  fiimies. 


L'Institut  a  microfilm^  le  meilleur  exemplaire 
qu'il  lui  a  iti  possible  de  se  procurer.  Les  details 
de  cet  exemplaire  qui  sont  peut-dtre  uniques  du 
point  de  vue  bibliographique,  qui  peuvent  modifier 
une  image  reproduite,  ou  qui  peuvent  exiger  une 
modification  dans  la  methods  normale  de  fiimage 
sont  indiqu6s  ci-dessous. 

□   Coloured  pages/ 
Pages  de  couleur 

□    Pages  damaged/ 
Pages  endommagdes 

□    Fages  restored  and/or  laminated/ 
Pages  restauries  ^t/ou  pelliculdes 


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to  the 


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Pages  discoloured,  stained  or  foxed/ 
Pages  dicolories,  tachet^es  ou  piqudes 


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Pages  d^tach^es 

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Transparence 

□    Quality  of  print  varies/ 
Quality  inigale  de  I'impression 

□    Includes  supplementary  material/ 
Comprend  du  materiel  suppl^mentaire 

□    Only  edition  available/ 
Seule  Edition  disponible 


D 


Pages  wholly  or  partially  obscured  by  errata 
slips,  tissues,  otc,  have  been  refilmed  to 
ensure  the  best  possible  image/ 
Les  pagan  totalement  ou  partiellement 
obscurcies  par  un  feuillet  d'errata,  une  pelure, 
etc.,  ont  M  film6es  A  nouveau  de  fapon  i 
obtenir  la  meilleure  image  possible. 


Th«  Ir 
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Th«  copy  film«d  h«r«  has  bMn  roproduead  thanks 
to  tha  ganarosity  of: 

Dana  Porter  Arts  Library 
University  of  Waterloo 

Tha  Imagas  appaaring  hara  ara  tha  bat.t  quality 
poasibia  considaring  tha  condition  and  lagibiiity 
of  tha  original  copy  and  in  Icaaping  with  tha 
filming  contract  spaciflcationa. 


Original  copias  in  printad  papar  covars  ara  filmad 
baginning  with  tha  front  covar  and  anding  on 
tha  last  paga  with  a  printad  or  illustratad  impraa- 
sion,  or  tha  back  covar  whan  appropriata.  All 
othar  originaS  copiaa  ara  filmad  bagin.ning  on  tha 
first  paga  with  a  printad  or  illustratad  irripraa- 
sion,  and  anding  on  tha  last  pcga  with  a  printad 
or  illuatratad  impraasion. 


Tha  iaat  racordad  frama  on  aach  microficha 
shall  contain  tha  symbol  — ^(moaning  "CON- 
TINUED"), or  tha  symbol  V  Imaaning  "END"), 
whichavar  appiias. 

Maps,  platas,  charts,  ate,  may  ba  filmad  at 
diffarant  raduction  ratios.  Thosa  too  larga  to  ba 
antiraly  includad  in  ona  axpasura  ara  filmad 
baginning  In  tha  uppar  laft  hand  cornar,  laft  to 
right  and  top  to  bottom,  as  many  framaa  aa 
raquirad.  Tha  following  diagrams  illustrata  tha 
mathod: 


L'axamplaira  film*  fut  raproduit  grftca  A  la 
gAnArosit*  da: 

Dana  Porter  Arts  Library 
University  of  Waterloo 

Laa  imagas  sulvantas  ont  it6  reproduitas  avec  la 
plus  grand  soin,  compta  tanu  da  la  condition  at 
da  la  nattatA  da  l'axamplaira  film*,  at  an 
conformity  avac  las  conditions  du  contrat  da 
filmaga. 

Laa  axamplairas  originaux  dont  la  couvertura  an 
papiar  ast  imprimte  sont  fiim^s  an  commandant 
par  la  pramiar  plat  at  an  tarminant  soit  par  la 
darnlAre  paga  qui  comporta  una  amprainta 
d'imprassion  ou  d'iilustration,  soit  par  la  sacond 
plat,  salon  la  cas.  Toua  las  autras  axamplairas 
o/iginaux  sont  filmta  an  commandant  par  la 
pramlAra  paga  qui  con^  porta  una  amprainta 
d'impraasion  ou  d'iilustration  at  an  tarminant  par 
la  darniira  paga  qui  comporta  una  talla 
amprainta. 

Un  daa  symbolas  suivants  apparaitra  sur  la 
darnlAra  imaga  da  chaqua  microficha,  salon  la 
cas:  la  symbola  — ^>  signifia  "A  SUIVRE  ",  la 
symbols  V  signifia  "FIN  ". 

Laa  cartas,  planchaa,  tablaaux,  ate,  pauvant  dtre 
filmte  i  das  taux  da  rMiiction  diff^rants. 
Lorsqua  ia  documant  ast  trop  grand  pour  Atra 
raproduit  an  un  saul  clich^b,  il  ast  film*  *  partir 
da  I'angla  sup^riaur  gaucha,  da  gaucha  i  droita, 
at  da  haut  an  baa,  mn  pransnt  la  nombra 
d'imagas  nAcaasaira.  Las  diagrammas  suivants 
illustrant  la  mAthoda. 


irrata 
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1 

2 

3 

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6 


INVERl 


J.  I 

Pi 


h 


A  TEXT-BOOK 


or 


INVERTEBRATE    MORPHOLOGY 


BY 

J.  PLAYFAir'McMURRICH,  M.A.,  Ph.D. 

Professor  of  Anatomy  in  the  University  of  Michigan 


SECOND    EDITION,  REVISED 


\ 


Q. 

U 


0^S 


NEW    YORK 

HENRY  HOLT  AND  COMPANY 
1896 


Copyright,  1894, 

BY 

Henry  Holt  &  Co, 


KinRRT   DRUMMONF,,    Et-ECTROTVPER   AND   PR'NTER,   NEW   YORK. 


The  Morp 

either  from  tl 

the  zoologica 

to  recommen( 

method  has  p 

the  subject  i 

method  empl 

present  work 

has   been   fol 

peculiarities  c 

iug  the  brick 

uuite  them  to{ 

opportunity  h 

to  the  compar 

I  affinities  of  th( 

A  word  is  ] 

jadopted,  which 

I  usually  empio;; 

liimple  of  Claus 

Ithan  twelve  of 

iber  has  resulte 

iuized,  namely,  1 

former  it  has  h 

collection,  and 

tt  is  true  that 

)hyl()<reuetic  ai 

retention,  then 

should  also   be 

jtory  to  retain  tl 

md  to  divide 

i^Iatyhelminthe 

Same  rank  as  : 

piniilar  degrees 


PREFACE. 

The  Morphology  of  Invertebrate  Animals  may  be  treated 
either  from  the  staudpoiut  of  Comparative  Anatomy  or  from 
the  zoological  side,  and  either  method  of  treatment  has  much 
to  recommend  it.     In  my  experience,  however,  the  zoological 
method  has  proved  most  satisfactory  for  the  presentation  of 
the  subject  to  students,  inasmuch  as  it  is  necessarily  the 
method  employed  in  the  laboratory,  and  accordingly  in  the 
present  work  that  plan  of  presenting  the  facts  of  morphology 
has   been   followed.      A   bare    statement   of    the    structural 
peculiarities  of  the  various  groups,  however,  is  simply  collect- 
ing the  bricks  and  stones  without  the  mortar  necessary  to 
unite  them  together  into  a  substantial  edifice,  and  where  the 
opportunity  has  presented  itself  attention  has  been  directed 
to  the  comparative  significance  of  various  organs  and  to  the 
affinities  of  the  various  groups. 

^  A  word  is  perhaps  necessary  in  regard  to  the  classification 

aaopted,  which  presents  many  radical  changes  from  the  schemes 

lusually  employed.     For  the  larger  groups,  following  the  ex- 

lample  of  Claus,  the  term  type  has  been  employed,  and  no  less 

Ithan  twelve  of  these  types  are  adopted.     This  increased  num. 

Iber  has  resulted  from  a  division  of  two  groups  usually  recog- 

•iiized,  namely,  the  Vermes  and  the  Arthropoda.    As  regards  the 

former  it  has  long  been  acknowledged  to  be  a  heterogeneous 

^oilection,  and  its  retention  is  to  be  regarded  as  a  survival 

It  IS  true  that  the  forms  assigned  to  it  do   present  certain 

Dhylogenetic  afhnities ;  but  if  tliis  is  to  be  the  reason  for  its 

retention   then  the  Mollusca  and  Prosopygia  (Molluscoidea) 

should  also  be  assigned  to  it.     It  has  seemed  more  satisfac- 

ory  to  retain  the  Mollusca  and  Prosopygia  as  distinct  grou,)s, 

^iid  to  divide  the  Vermes  into    several  types,   such  as  the 

eiatyhelnunthes,  Nemathelminthes,  and  Annelida,  each  of  the 

ame  rank  as  the  Mollusca,  and  presenting   approximately 

piniiiar  degrees  of  aftinity  among  themselves. 


I 


i 


^mii#tmpi 


I 


PREFACE. 


As  to  the  Artliropoda,  its  right  to  exist  as  a  group  coordi- 
nate with,  for  iustanee,  the  Mollusca  has  been  questioned  by 
several  authors.  IJudoubtedl}'  iu  this  case  also  mauy  similar 
structural  features  obtain  among  the  various  members  of  the 
group,  but  embryology  has  indicated  a  probability  of  a  more 
or  less  independent  origin  of  two  Arthropodan  groups  usually 
regarded  as  closely  related,  namely,  the  Arachnida  and  the 
Tracheata  proper.  Apparently  the  former  have  originated 
from  Crustacean  ancestors,  while,  if  the  supposed  significance 
of  Peripatus  be  accepted,  the  Tracheates  are  to  be  traced  back 
to  Aunelidan  forebears,  antl  for  the  purpose  of  calling  the 
attention  of  the  student  to  this  probable  phylogeny  the 
Crustacea,  Arachnida  and  Tracheata  have  been  regarded  as 
distinct  types  coordinate  with  the  Annelida  and  Mollusca. 

A  book  of  this  kind  must  necessarily  be  highly  tinged  with 
the  individual  opinions  of  the  writer,  and  for  these  indulgence 
must  be  craved.  So  far  as  the  facts  are  concerned  every 
care  has  been  taken  that  they  should  be  accurate  and  as 
far  as  possible  up  to  date  Avith  the  most  recent  iuvestigations. 
Errors  have  no  doubt  crept  in,  a  misfortune  almost  inevitable 
from  the  mass  of  material  which  mxist  pass  under  consideratiou 
during  the  progress  of  the  work,  and  for  these  again  indul- 
gence must  be  asked. 

Refrjxining  from  further  apologies,  the  more  pleasant  duty 
remains  of  thanking  the  many  friends  Avho  have  so  kindly 
aided  the  work  by  suggestion  or  otherwise,  and  especially 
those  who  have  permitted  the  use  of  figures  taken  from 
special  papers.  A  large  number  of  the  figures  employed 
are  original  and  the  great  majority  have  been  especially 
drawn  for  this  work,  the  attempt  being  made  to  diagramma- 
tize them  to  a  greater  or  less  extent  for  the  sake  of  clearness. 
In  all  cases  where  figures  have  been  borrowed  the  original 
authorsliip  has  been  duly  acknowledged. 

Finally,  I  desire  to  make  public  recognition  of  my  indebt- 
edness to  my  wife  for  the  invaluable  assistance  she  has  ren- 
dered in  many  ways  during  the  progress  of  the  work. 

J.  Playfair  McMurrich. 

Univeusity  of  Miciiioan, 
September,  1894. 


Chapter  I 


Chapter  I] 


Chapter  V 


Chapter  V 


TABLE  OF  CONTENTS. 


Chapter  I,     Protoplasm  and  the  Cell 

Composition  of  Protoplasm,  pp.  1-3.     St'iictuie  of  Ibe  Cell, 
pp.  4-8.     Cell-division,  pp.  9-12.    Literature,  p.  12. 


PAGES 

1-12 


Chapter  II,    The  Subkinguom  Protozoa.  13-40 

The  Class  Rhizopoda,  pp.  14-24.  The  Class  Sporozoa,  pp.  34- 
28.  The  Class  Flagellata,  pp.  28-33.  The  Class  Infusoria, 
pp.  33-38.  Synoptical  Classitication,  pp.  38, 39.  Literature, 
pp.  39,  40. 

Chapter  III.    The  Subkingdom  Metazoa 41-63 

Individuality  of  the  Metazoa,  pp.  41-42.  Sexual  Reproduction, 
pp.  42-51.  The  Segmentation  and  Early  Development  of 
the  Ovum,  pp.  51-58.  Non-sexual  Reproduction  of  the 
Metazoa,  pp.  58-60.  Alternation  of  Generations,  pp  60-63. 
Literature,  p.  63. 


Chapter  IV.    Trichoplax,  the  Dicyemid.e  and  the 
Orthonectida 

Trichoplax,  pp.  63.  64.     The  Dicyeniida!,  pp.  64,  65.     The  Or- 
thonectida, pp.  65-67.     Literature,  p.  67. 


63-67 


Chapter  V.    The, Type  C(elentera 68-119 

The  Subtype  Porifera,  pp.  69-76.  The  Subtype  Cnidaria,  pp. 
76-115.  The  Class  Hydromedusa\  pp.  78-97.  The  Class 
Scyphomedusfc,  pp.  97-104.  The  Class  Authozoa,  pp.  104- 
115.  Synoptical  Classification,  pp.  115-117.  Literature, 
pp.  118,  119. 

Chapter  VI.    The  Ctexophora 120-126 

Description  of  the  Group,  pp.  120-126.  Synoptical  Classifica- 
tion, p.  120.     Literature,  p.  126. 


VI 


TABLE  OF  CONTENTS. 


PAOES 

Chapter  VII     The  Type  Platyhelminthes 127-171 

The  Cliiss  Turbellaiia,  pp.  ] 30-143.  The  Class  Trematoda,  pp. 
143-153.  The  Class  Cesloda,  pp.  152-161.  The  Class 
Nemertiua,  pp.  162-169.  Synoptical  Classificatioii,  pp. 
169.  170.     Literature,  pp.  170,  171. 

Chapter  VIII.    The  Type  Nemathelminthes 172-183 

The  Class  Nematoda,  pp.  173-179.  The  Class  Acanthocephala, 
pp.  179-183.  Synoptical  Classification,  pp.  182,  183.  Lit- 
erature, p.  183. 

Chapter  IX.    The   Order  Echinodera;  the   Class 

Ch^tognatha;    the    Class    Rotifera;    the 

Order  Gastrotricha  ;    and  Dinophilus 184-201 

The  Order  Echinodera,  pp.  184-186.  The  Class  Chietoguatha, 
pp.  186-189.  The  Class  Rotifera,  pp.  189-195.  The  Order 
Gastrotricha,  pp.  195-198.  The  Genus  Dinopliilus,  pp. 
198-200.  Synoptical  Classification,  p.  200.  Literature,  p. 
201. 

Chapter  X.    The  Type  Annelida 202-253 

The  Class  Chaetopoda,  pp.  204-227.  The  Class  Hirudinea,  pp. 
?28-237.  The  Class  Gephyrea,  pp.  237-243.  The  Class 
Myzostomeoe,  pp.  244-246.  The  Class  Phorouidse,  pp.  247- 
251.  Synoptical  Classification,  pp.  251,  252.  Literature, 
pp.  252,  253. 

Chapter  XI.    The  Type  Prosopygia 254-275 

The  Class  Polyzoa,  pp.  255-268.,  The  Class  Brachiopoda,  pp. 
268-374.  Synoptical  Classification,  p.  274.  Literature,  p. 
375. 

Chapter  XII.     The  Type  Mollusca 27G-367 

The  General  Characteristics  of  the  Type,  pp.  276-284.  The 
Class  Aniphineura,  pp.  284-293.  The  Class  Gasteropoda, 
pp.  293-333.  The  Class  Scaphopoda,  pp.  322-336  The 
Class  Pelecypoda,  pp.  326  340.  The  Class  Cephalopoda, 
pp.  340-363.  The  Affinities  of  the  Mollusca,  pp.  363,  363, 
Synoptical  Classification,  pp.  363-365.  Literature,  pp. 
365-367. 

Chapter  XIII.    The  Type  Crustacea 368-434 

The  General  Cliaracteristics  of  tlie  Type,  pp.  308-385.  The 
Class  Entomostraca,  pp.  385-403.  The  Class  Malacostraca, 
pp.  403-417.  The  Development  and  Alfinities  of  tiio  Crus- 
tacea, pp.  417-423.  Synoptical  Classification,  pp.  423,434. 
Literature,  i)p.  434-427.  The  Order  Xiphosura,  pp.  437- 
434.     Literature,  p.  434. 


Chapter  X 


Chapter  X 


Chapter  X^ 


[Index  of  Pj 
(Index  of  Si 


i 


PAOES 

7-171 


2-183 


i-201 


3-253 


1-275 


TABLE  OF  CONTENTS. 


vU 


PAQEB 


Chapter  XIV.    The  Type  Arachnida 435^468 

Tbe  General  Characteristics  of  the  Type,  pp.  435-441.  Descrip- 
tion of  the  Various  Orders,  pp.  441-450.  'I'Jie  Phylogeny 
of  the  Arachnida,  pp.  456-438.  Synoptical  Classiflcation, 
pp.  458,  459.  Literature,  pp.  459,  460.  The  Order  Peuta- 
stomidsB,  pp.  461-463.  The  Order  Pyciiogonida,  pp.  483- 
466.  The  Order  Tardigrada,  pp.  466-468.  Literature,  d. 
468. 

Chapter  XV.    The  Type  Tracheata 4G9-530 

The  General  Characteristics  of  the  Type,  pp.  469-474.  The 
Class  Protracheata,  pp.  474-480.  The  Class  Myriapoda. 
pp.  480-487.  The  Class  Insecta,  pp.  487-522.  The  Phy! 
logeny  of  the  Tracheata,  pp.  523-525.  Synoptical  Classifl- 
cation,  pp.  525-528.     Literature,  pp.  528-530. 


531-595 


j-367 


\  Chapter  XVI.    The  Type  Echinoderma 

The  General  Characteristics  of  the  Type,  pp.  531-540.  The 
Class  Crinoidea,  pp.  .541-551.  The  Class  Asteroidea,  pp. 
552-560.  The  Class  Ophiuroidea,  pp.  561-570.  The  Class 
Echinoidea,  pp.  570-584.  The  Class  Holothuroidea,  pp. 
584-590.  The  Phylogeny  of  the  Ecliinodernia,  pp.  590- 
592.  Synoptical  Classiflcation.  pp.  592,  593.  Literature 
pp.  593-595. 

[Chapter  XVII.    The  Type  Protochordata 596-G41 

The  Class  Hemichorda.  pp.  596-608.  The  Class  Cephalochorda. 
pp.  608-618.  The  Class  Urochorda,  pp.  618-639.  Synop- 
tical Classification,  pp.  639,  640.     Literature,  pp.  640,  641. 

[Index  of  Proper  Names 


IIndex  of  Subjects. 


643-653 
654-661 


3-434 


-mt^m»*> 


iNv; 


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animal,  ^ 

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rate  kno 

this  subs 

it  as  a  SI 

number 

of  which 

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since  our 

mining  ai 

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relationsl 


INVERTEBRATE    MORPHOLOGY. 


CHAPTER  I. 


PROTOPLASM  AND  THE  CELL. 

In  the  exainiuatiou  of  organisms  presenting  the  series  of 
phenomena  which  we  term  life,  the  invariable  presence  of  a 
peculiar  semi-fluid  transparent  or  hyaline  substance  becomes 
quickly  apparent.  Whether  the  organism  be  a  plant  or  an 
animal,  whether  it  be  of  the  simplest  or  of  the  most  complex 
organization,  it  is  still  composed  of  this  substance,  which  is 
known  as  protoplasm,  and  it  may  be  said  that  so  far  as  our 
knowledge  extends  life  never  exists  except  in  association  with 
this  material.  Protoplasm  is  "  the  physical  basis  of  Life," 
and  it  becomes  of  great  importance  that  its  nature  should  be 
fully  understood,  in  order  that  the  results  of  its  activities. 
Life,  may  become  more  intelligible. 

Much  has  yet  to  be  accomplished,  however,  before  an  accu- 
rate knowledge  of  the  structural  and  chemical  characters  of 
this  substance  is  obtained,  and  indeed  it  is  incorrect  to  regard 
it  as  a  substance,  since  it  is  rather  the  aggregate  of  a  large 
number  of  exceedingly  complex  chemical  compounds,  none 
of  which  are  sufficiently  known.  From  the  very  nature  of 
things  it  is  impossible  at  present  to  get  a  correct  idea  of  these 
substances  and  the  relations  which  they  bear  to  one  another, 
since  our  present  analytical  methods  are  not  capable  of  deter- 
mining and  isolating  them  in  living  protoplasm  and  the  mere 
act  of  subjecting  ])rotoplasm  to  analysis  destroys  those  very 
relationships  which  are  the  cause  of  the  vital  manifestations. 


IN  VERTEBRA  TE  MORPIIOL  OGY. 


Dead  protoplasm  is  sometliiug  very  dili'ereut  from  living  pro- 
toplasm, and  our  present  knowledge  only  imperfectly  extends 
to  this  much-altered  material. 

Furthermore  even  in  the  dead  material  the  chemist  has  to 
deal  not  only  with  the  complex  substances  which  constitute 
protoplasm  proper,  but  also  wicli  numerous  secondary  prod- 
nets  either  in  the  process  of  being  built  up  into  protoplasmic 
molecules   or  else    resulting   from  the  destruction   of   these 

I  molecules-     For  both  these  processes  are  contimally  going 

I  on,  the  living  organism  continually  uniting  simple  chemical 
compounds  to  form  ne-v  complex  molecules,  a  process  known 
as  anabolism,  and  resulting  in  growth  ;  and  just  as  continually 
it  is  resolving  into  simpler  comijounds  the  complex    mole- 

[  cules  already  formed,  a  process  known  as  catabolism,  and 
resulting  in  the  manifestation  of  energy  in  its  various  forms, 

;  such  as  heat,  motion,  electricity,  and  even  light.     Growth  and 

I  the  manifestation  of  energy  are  then  two  most  important 
phenomena  exhibited  by  living  organisms,  standing  in  oppo- 
sition to  one  another  and  determining  the  general  condition 
of  the  organism.  If  anabolic  changes  are  the  more  active, 
then  the  animal  or  plant  grows,  as  we  express  it,  adds  new 
protoplasm  and  increases  in  size  ;  if  the  anabolic  and  catabolic 
changes  are  practically  equal  in  amount,  stability  results  ; 
Avliile  the  preponderance  of  catabolism  leai^s  to  a  lessening 
of  misterial,  and  finally  to  what  we  term  death.  These 
changes  constitute  a  cycle  occurring  in  the  life-history  of 
probably  every  organism  and  causing  the  periods  which  we 

■  denota  as  youth,  matarity,  and  old  age. 

Dead  protoplasm  th-^u,  together  with  the  anabolic  and 
catabolic  constituents  which  are  inextricably  associated  with 
it,  wil  b«>  f(  rnd  on  analysis  to  consist  to  a  largo  extent  of  tln^ 
chemical  elements  Carbon,  Hydroy;en,  0.:ygen,  and  Nitrogen, 
together  with  Sulphur  and  Phospl orus,  as  wall  as  a  number 
of  substances  ])resent  in  varyiiig  amounts,  such  as  Chlorine, 

•Potassini.i,  Sodium,  Iron,  Calcium,  and  Maghesium.  Exactly 
l)ow  these  various  elements  are  united  together  it  is  dilVicult 
to  detei'miii(»,  but  es))eciu]  importance  has  beon   assigned  to 

t' the  (\  ii,  (),  N,  Jllid  S  i'<)iii|i()irn(ls  whirii  tHCiil'  Mill  wliich  foriii 
a  group  jf  cheuiicul  compounds  known  as  ]*roteids.     Of  sucli 


compou 

Nuclein, 

probabl 

the    pre 

Plastiu 

importai 

Plastiu 

trated  alk; 

and  eonsis 

teristic  of 

miclcus,  o 

closely,  be 

t     cliomical  e 

f    tlio  niicleii 

1^    seems  pi'ol 

I    from  wliici 

;    compounds 

I        With 
ous  salts, 
Potassiui 
other  sue 
to  estima 
dead  has 
As  rej: 
moderate 
and  more 
peripliera 
than  the 
cially  dis 
eiuloplasi 
usually  vi 
prot()[)lasi 
and  knowi 
sin)plor  oi 
toplasm,  )i 
tnre,  the 
i  occupyiiig 
.Jetm   later 
:=  protoplasrj 
protoplusi] 


PROTOPLASM  AND  THE  CELL. 


3 


compouuds  several,  sncli  as  Albumin,  Globulin,  Fibrin,  Plastin 
Nueleiu,  have  been  isolated  from  protoplasm,  som'e  being 
probably  secondary  products  resulting  from  the  alteration  of 
the  protoplasmic  molecules  proper,  but  others,  such  as 
Plastin  and  Nueleiu,  are  especially  constant,  and  seem  to  be 
important  constituents  of  the  protoplasmic  complex. 

Plastin  ronns  wlien  isolated  a  sticky  fibrous  mass,  i-soluble  in  concen- 
trated alkaline  solutions  atui  unaffected  bytlie  peptic  and  tryptic ferments 
and  consists  of  C.  H,  O,  N,  S,  and  P.     Nuclein  is  more  especially  charac- 
teristic of  a  speca.  portion   or  modification   of  protoplasm  termed  the 
imcleus  of  which  more  will  be  said  hereafter,  and  resembles  plastin  very 
c  osely,  beniK,  however,  less  insoluble  than   it,  and  consists  of  the  same 
chemical  elements.     Analyses  of  these  substances,  however,  differ  Kre-itlv 
the  nuclein  from  spermatozoa,  for  instance,  containing  no  sulphur  •  ami  ii 
seems  probable  not  only  that  they  differ  materially  according  to  the  source 
irom  whicn  they  are  obtained,  but  also  that  they  are  not  reaMy  chemical 
compounds,  but  a  mixture  of  several  highly  complex  substances. 

With  these  proteids,  then,  there  exist  in  protoplasm  vari 
ous  salts,  such  as  Potassiuiu,  Sodium,  and  Calcium  phosphate 
Potassnim  and   Sodium  chloride,  Magnesium   sulphate,  and 
other  such  salts,  the  exact  significance  of  which  it  is  difficult 
to  estimate.     Fow  living  protoplasm  differs  chemically  from 
dead  has  not  up  to  the  present  been  accurately  determined 

As  regards  its  general  structure  protoplasm  appears  as  a 
moderately  consistent  jelly-like  substance,  usually  coh.rless 
and  more  or  less  granular   in   appearance.     As  a  rule   the 
peripneral  portion  of  a  mass  of  protoplasm  is  less  granular 
than  the   central,  appearing  therefore   clearer,  and  is   espe 
cndly  distinguished  as  the  ectoplasm  from  the  more  opaque 
endoplasm.     Imbedded    in    the  eudoplasm  are    to  be  found 
usually  various  bodies,  the  products  of  the  activities  of  the 
pintoplasm,    such   as   largo,  clear   spaces    occupied   by  fluid 
nnd  known  as  vacuoles,  food-particles  „f  various  kiml.s  in  the 
simpler  organisms,  starch  granules  and  crystals  in   idant-,),... 
toplasm,  and  depositions  ,,f  pigment.     One  particular  struc- 
ture, the  nucleus Jiowever,  seems  to  be  invariablv  present 

l-HH-npying  the  central  portion   of  the  mass,  and,  as   will   bj 
.^een  later,  playing  u  very  important  lole  in  the  life  of  the 

^  pro  n|>  asm.     it  is  ind-ed  a  specially  nio.liaed  portion  of  the 
piotoplasm   and  cannot,  therefore,    be   placed   in    the    same 


1 


i 


/iV^  VEUTEBltA  TE  MORPIIOLOG  Y. 


category  as  the  vacuoles  autl  other  accidental  or  secoudaiv 
constitueuts  which  have  been  mentioned,  and  every  mass  of 
protoplasm  may  be  considered  as  consisting  of  tv/o  essential 
parts,  the  protoplasm  proper  or  cytoplasm  and  the  special 
modification  of  it,  the  nucleus,  Avhich  for  convenience  is 
termed  the  caryoplasm.  Such  a  combination  of  cytoplasm 
aud  caryoplasm  forms  what  is  technically  known  as  a  cell,  and 
ail  living  organisms  are  composed  of  one  or  more  such  struc- 
tures, which  are  to  be  regarded  therefore  as  morphological 
units. 

If  the  more  intimate  structure  of  the  cytoplasm  of  such  ii 
unit  or  cell  (Fig.  1)  be  examii^ed,  disregarding  the  various 


urn 


-,  nl 


Pig.  1.— Diagram  bhowtno  the  Structurk  op  an  Animal  Cell. 

c  =  cc'iitrosoiuo.  m  —  iniciosoine. 

cl  ~  cylolyiiiph.  nl  =  nucleolus. 

cr  —  cbroumtia  nm  =  niKleiir  meinbiane. 

r  =  reticulum. 

secondary  constituents  it  may  enclose,  it  will  be  found  to 
consist  of  a  network  of  oxceodiiigly  fine  fibvils,  along  Avhicli, 
and  more  especially  at  the  points  where  two  or  more  of  them 
meet,  are  to  be  found  minute  granules  which  stain  deeply  with 
the  ordinary  niicrosco})ical  staining  reagents.  The  fibrils 
constitute  the  reticuhun  (Fig.  1,  r)  of  the  cytoplasm,  and  tln' 
granules  are  termed  the  micrnsonics  (iii).  The  reticuluni 
seenis  to  be  formed  princii)ally  of  the  ^.loteid  substance 
already  mentioned  as  ])lastin,  and  its  meshes  are  occupied  by 
a  more  fluid  substance  >vhich  has  been  termed  the  cyin- 
hjmph  {cl). 


Several  o] 

[plasm,  ill  ad 

I  compared  to 

*cytolymph. 

I  fibrils  of  varj 

Itlio  retiouluii 

■According  to 

•in  the  cytopl; 

-less  matrix  ii 

^sometimes  se 

It  he  upholder 

Ircga'-ding  tin 

lits  .structure 

seems  probabl 

products  of  tl 

ordinate  valu 

more  nearly 

lust  be  admit 
true  reticulufr 
In  some  cases 
Au  imitatii 
|;ure  of  thickt 
bhioride  of  so 
globules  each 
tefraetive  indi 
he  cytolympli 
bo  collect  at  t 
pgethcr,  and 
tinder  certain  ( 
|olumnar  form 

possible  that 
eticular  theon 
le  a  sjKxigy  .sti 
ivided  into  •,\ 
llastin.  At  ])i 
bost  acc!n'atel; 
Ssioiially  acccj 

The  cary( 

bont  the  mi 

iUihles  it,  t 

usually  ro 

fongated,  h( 

liirs,  .iiiii  is 

i  iin'uibrune 


PROTOPLASM  AND  TUE  CELL. 


Several  opinions  have  been  given  in  regard  to  the  structure  of  the  cyto- 
[plasm,  in  addition  to  tliat  here  presented,  according  to  whicli  it  may  l>e 
jconipared  to  a  sponge  the  meshes  of  wliose  networlc  are  occupied  by  the 
Icytoiympli.    According  to  anotlier  view  it  is  composed  of  a  number  of 
jtibriis  of  varying  lengtiis  imbedded  in  a  matrix,  thetibrils  corresponding  to 
Ithe  reticulum  of  tlie  reticular  tlieory  and  tlie  matrix  to  tlie  cytolympli 
[According  to  still  another  theory  which  rests  on  tlie  appearance  produced 
jin  the  cytoplasm  by  a  special  method  of  treatment,  there  is  present  a  color- 
Jess  matrix  in  which  are  imbedded  numerous  exceedingly  small  granules 
sometimes  scattered  and  somelimes  united  together  into  chains     Indeed 
tiie  upholder  of  this  granular  theory  has  carried  his  view  to  the  extent  of 
m-eganiing  the  granules  as  structural  units  of  which  the  cell  is  composed 
|Kts  structure  being  comparable  to  that  of  a  zoogloia  of  micrococci      It 
«^eems  probable,  however,  that  the  granules  are  to  a  large  extent  secondary 
products  of  the  activities  of  the  cytoplasm  and  have  therefore  but  a  sub 
M-d-.nate  value  in  its  composition.      The  reticular  theory  seems  to  stand 
hiiore  nearly  in   harmony  with  the  majority  of  observations,   thou-rh  it 
ynust  be  admitted  that  some  observers  do  not  seem  to  have  perceived  the 
true  reticulum,  confining  their  attention  to  the  coarser  network  produced 
pi  some  cases  by  extensive  vacuolization  of  the  cell. 

An  imitation  of  tiie  cytoplasm  ha.  been  recently  obtained  by  the  mix- 
ture of  tiiickened  olive-oil  with  a  solution  of  potassium  carbonate  or  of 
chIor.de  of  .sodHim,  the  watery  solution  taking  the  form  of  polyhedral 
globules  each  surrounded  by  a  thin  layer  of  oil  which  from  its  lii-dle 
befrac  ,ve  index  gives  the  appearance  of  the  plastin  reticulum  surrounding 
the  cy  ..lymph,     hdid  particles  finely  .livided  and  mixed  with  tlie  nil  teud 

0  collect  at  the  points  where  the  oil-films  of  three  of  the  glolmles  come 
logoth-r,  and  resemble  the  microsomes,  whil,-  it  is  further  noticeable  tC 
bnder  certain  con.lit.ons  the  superficial  globuh-s  of  th.  ,.,„,dsion  take  on  a 
[olumnar  form  and  may  be  compared  with  the  ,      .pla.sm  of  the  cell      It 

imss.hle  that  the  cytoplasm  may  have  this  structure,  in  which  case  the 
itu  ula,  theory  would  n>q,iire  to  be  moditied,  since  there  would  no  longer 
ha  spongy  , structure,  but  rather  an  eu.ulsion  in  which  the  cvtolymplfi 
Jvi  ed    imo  a  number  of  globules  eac-h  surrounded  by  a  thin  ^"^r  .l 
f^^a.  in.     At  ,,r,.s,.n  ,  howev.r,  the  reticular  theory  seems  to  correspond 

Thcy^aryoplastii  or  nuolons,  as  already  stated,  lies  usually 
I.OP  the  nmldle  of  the  cytoplasm  an.l  to  a  certain  extent  re- 
^nMenit,  thou^rJi  it  presents  certain  peculiar  feaUires  It 
i  usually  round  or  oval,  though  occasionally  it  n.ay  assume 
Jongated.  horseshoe-shaped,  moniliforni,  or  even  f.ranchimr 
^nns,  uui  iH  as  H  nde  clearly  nnirke.i  off  from  the  cvtoi.lasm  l.v 

1  membrane  (I  ,g.  1.  ,nn>\  whi.h.  lM>wever.  at  certain  periods  .if 


6 


INVERTEBRATE  MORPHOLOGY. 


nuclear  activity  seems  to  disappear,  a  new  one  subsequently 
forming.  Traversing  the  space  enclosed  by  the  membrane, 
so  as  to  form  a  network,  are  fibres  which  do  not  stain  very 
deeply  with  the  usual  staining  fluids  and  which  are  composed 
of  a  substance  termed  linin,  which  does  not,  however,  appear 
to  differ  essentially  from  the  plastin  of  the  cytoplasm.  In- 
deed it  is  not  improbable  that  the  linin  network  is  con- 
tinuous through  the  nuclear  membrane  with  the  plastin 
reticulum  and  that  both  are  identical,  as  is  also  the  caryo- 
lymph  contained  in  the  meshes  of  the  linin  with  the  cyto- 
lympli. 

A  more  characteristic  substance  is  the  chromatin  (Fig. 
1,  cr),  so  called  from  the  strong  aflinities  it  shows  for  many 
staining  fluids,  such  as  carmine,  hsematoxylin  solutions,  and 
certain  aniline  stains.  It  seems  to  consist  of  the  substance 
nuclein,  already  alluded  to,  and  in  the  resting  nucleus  forms 
a  reticulum  intimately  associated  with  the  linin  network, 
which  it  usually  to  a  considerable  exteut  obscures.  Where 
the  various  strands  of  the  network  meet,  thickenings  of  the 
chromatin  sometimes  occur,  producing  densely  staining 
bodies  (r?i)  to  which  the  term  nucleoli  is  given,  though  it  is 
probable  that  bodies  of  a  somewhat  difl'erent  composition 
are  also  included  under  this  name ;  for  there  are  usually  to 
be  found  in  the  nucleus,  imbedded  in  the  substance  of  the 
network,  one  or  more  spherical  bodies  whose  chemical  re- 
actions differ  noticeably  from  those  of  the  chromatin  nucleoli, 
the  substance  of  which  they  are  composed  being  termed 
piranndein  or  py renin. 

There  are  then  in  the  coll  the  following  structural  con- 
stituents : 


I.  Cytoplasm 


[  membrane  (cell-wall), 
■I  reticulum  (plastin), 
(  cytolymph. 


membrane, 
reticulum  (linin), 
II.  Caryoplasm  :  -\  caryolymph. 

i    (:iiri;iii;i,tiii  Iji'-tvvork  fuucloiu), 

(^nucleoli  (nuclein  and  parauucloiu). 


In  additioi 

be  mentioned 

undergoing  m 

various  restiuj 

kinds  of  endo 

structure  kno\ 

an  exceedingly 

stain  with  the 

deuce,  but  has 

such  as  safran 

centrosome  is  p 

even  more  mny 

the   neigh b(,rli( 

■slight  concavity 

ing   the   centroi 

especially   in    d 

■sphere,  and  froi 

directions,   whe 

^onibination  of  i 

niic  rays.     (See 

The  significance 

Domena  of  cell-divi 

'"'liiiml  into  at  tl 

'iiattor,  according  t( 

""clous  and  at  a  cei 

In  favor  of  this  vie^ 

"iicloiis  are  poiiitc( 

'louiiccd   during  col 

ti'dsonie  appearing  tc 

'livision  into  two  pai 

"'woino  is  a  cons! it ii 

''"  \vitli  (ho  luicloiis. 

i'lca  has  been  suggesl 

'"■  '<••"'«  than  ati  aggn 

iii'c  cytoplasmic  fil)fo 

'"'L'ur  along  their  coi 

"lioro  the  fibres  ineol 

"  ""iiy  l>e  pointed  out 

'"''I  liieir  powers  of  n 

lirrejrated  jnU-rnHomc:, 

tliiit  (ho  theory  cxpi 

'vpieal  aster  during  th 


PROTOPLASM  AND  TUB  CELL. 


.tructm-e  k„„w.  a.,  the  c.„tro.orn! m„lT- n     ''  "  "f 

r =r:  ~  ":r;  s  a^^^ 

the   iieij.liborhoocl   of   fl.a   ,      .  ^^^"'^^ed  m  the  cjtoplasm  in 

.li.*rfio„s,  whence  IheW     ^  ,  '  '''''■'''  P""*'  °»'  "'  "■' 

-.„biua.i,„  ooeulo!       "•*'•/'■':'"''  i-^  ■■'PPlie.l  to  tl,e 

...ie  ra,..     («ee  Kg  atlTr""'  "'       '     ""  "'"'  ""  "^■'"''''^^- 

The  significance  of  tlie  oentiwom*.  „;ii  i 
"-"ena  of  cell-division  are  nl^  ^I.  ,^  ^^^rbu^'T  "'""  '"  ^^"«- 
""l'"re(I  into  at  this  place.     Two  v^^   s  .^  '  •.     .     '  "'"'^'"  '"''^^  ''« 
'"atter,  according  to  one  of  which  tlT     T  ^*  '"  '"'^''^'■'^   *»  f''^ 

l-Ieusandat  /oertai;:,,  ri:  ^\^^e  nf  ::;r  ^'^^  '^^  ^^^'^'"  «»  t'- 
I"  favor  of  this  view  the  intim-.  P  -Z  /•  '"'!'"'''''  '«  extrndcd  from  it. 
-■-s  are  pointel  r^"  1  Z  T-  l''/'"  ^-'^^«-"'e  and  tha 
•—1  during  ceii-divLi  T^l  nvS  ""T,  "'^^'^'""^  '"- 
'-some  appearing  to  penetrat;,,:,'^/;^  rTtf.^'"'  ""  ^^"- 
'I'vision  into  two  parts.     AccordinL'  tr"...    i  ^'^  '"■'"^'  ''^'^""^  *'* 

'—  is  a  constituent  of  t^  ^  ^I  ^,1;    'j;^  r'''''^:  ""--••  ^'-  -n- 

i'loa  has  been  suggests   o  t  .o  off    t  n    ,  T       '"^  "'"pliHcation  of  this. 
"••  lf.s  tlKina,.4.vJi  n  of  evol  ^^""•-«ome  is  nothing  „,oro: 

h-^'tn-  ah,ng  their  course  an  ^---ve  ',ti  ,     f  '  /'"p  ""'"  ""^'••"-"nes  ■ 

I  «''">'o  the  fibres  meet.     This  i,'       .i  •"'"  '''"''^''^  '"'"^''^  ^e  found 

j  "  '"ay  be  pointcl  out  that  the  absn.c        n      ™'''^  '"  ''^''^'l  ''f-''..,  but 

'•-'  tlu-ir  powers  of  repro.l,    Mo    ?'.  1    .      '''''''"''''''"  "'  ''^^'  ^^'"^•''  ""ve 
L'r..L.n...d  U-rn.-, "''''''^  oxphcaWe  on  thi.  id..,   ,!-  -,  - 

p>i-' -tor  during  !h:d;^:;;:;i;;::^^^^^^^ 


8 


IN  VERTEBRA  TE  MORPHOL  00  Y. 


Sucli  a  combination  of  cytoplasm  and  caryoplasm  consti- 
tutes a  morphological  element  capable  of  carrying  on  all  the 
functions  of  life.     It  is  not  only  a  morphological  but  also  a 
physiological  element.      It  is   capable   of  assimilating   the 
necessary  substances  and  building  up  protoplasm  ;  metabol- 
ism and  the  consequent  evolution  of  energy  goes  on  in   it ;  it 
excretes  waste  products  ;  it  is  contractile  and  may  therefore 
be  capable  of  motion ;  it  responds  to  stimuli  of  various  kinds, 
or   in  other  words  it  is  irritable  ;   and,  finally,  it  is  capable 
of   reproduction.      The   question   naturally   arises,  however, 
whether  this  combination  of  the  two  substances  mentioned 
is  essential— whether,  that  is  to  say,  organisms  without  nuclei 
do  not  exist  and   manifest  all   the   phenomena   of   life.     At 
one  time  the  existence  of  unicellular  organisms  destitute  of 
a  nucleus  was  recognized,  the  term  cytode  being  applied  to 
them  to  distinguish  them  from  nucleated  cells.     Within  re- 
•cent   years,  however,  a   growing  skepticism   has   come    into 
existence  as  to  the  non-nucleate  character   of   these   organ- 
isms, the  recent   improvements  of   the  microscope   and  the 
application  of  modern  staining  reagents  having  revealed  the 
existence  of  nuclei  in  many  of  the  forms  at  one  tnne  regarded 
as  typical  cytodes.     It  would  perhaps  be  going   too  far   to 
state  that  cytodes  do  not  exist,  but  the  evidence  at  hand  indi- , 
ijates  that  their  existence  is  highly  problematical. 

This  conclusion  is  strengthened  by  the  results  which  have 
"been  obtained  irom  the  observations  of  artificially  produced 
cytodes.      Some   of   the   larger   unicellular   organisms   have 
been  cut  into  fragments   some   of   which    can   be   definitely 
shown  to  be  destitute  of  nuclear  or  caryoplasmatic  substance. 
In  such  cases   it   is  found  that  the   nucleated  fragments   if 
placed  under  proper  conditions  Avill  regenerate  and  carry  on 
Aheir  existence  as  before,  while  the  cytode  fragments,  thou^di 
manifesting  signs  of  life  for  a  considerable  length  of  tinie,^ 
will  not  regenerate  and  do  not  possess  the  power  of  repro-' 
duction.     The  nucleus  seems  to  possess  a  marked  rogulatiiif;; 
or  coofdinatiug  action  upon  the  cytoplasm,  coordinating  the: 
4inabolic  and  catabolic  activities  upon  which  the  coutiuuanci' 

of  life  depends.  , 

It  would  be  beyond  the  scope  of  the  present  work  to  enter! 
into  a  discussion  of  the  various  forms  of  physiological  activity 


of  the  eel 

tion,  must 

remarkabi 

the  dispro 

epigrammj 

watchword 

it  finds   it 

nucleus  e  m 

assumed  t' 

cell,  and  th 

of  the    anc 

previously 

is  accompa 

under    cert 

occur   Avith 

multinuclea 

of  tlie  cytc 

rated  witho 

might  be  e 

the  nucleus 

is  usually  p 

This  lati 

begin  as  a  s: 

deeper  and  ( 

ion  of  the  c 

that  each  of 

the  original 

is  rather  ra 

branes  of  th 

ion,  to  distin 

method  whi( 

jiiienomena  t 

w  applied. 

Starting  v 
nieutioued  oa 
K'lrded  as  afl 
|g<"tlierwithtl 
'"'itiii.  Thocf 
jKi'iuliially  Sep 
h'(>  fit  oppositt 


ch  have 
rocluced  | 
tis   liavei 
efiiiitel) 
bstauce. 
nents   if 
3any  oil 
,  thouj^'li 
of  tinio,^ 
»f  re  pro- 
gulatiiif;^ 
iting  the' 
tiuuauci' 

to  euterl 
I  activitv 


PROTOPLASM  AND  THF  CELL.  c 

of  the  cell,  but  one  of  its  physiological  functions,  reproduc 
tion,  must  receive  special  attention  in  conuectioL  w  th  the 
j^markable  sti.c  ural  changes  which  accompany  it  Si^ce 
the  disproval  of  the  doctrine  of  spontaneous  generation  «! 
epigrammatic  statement  Ononis  eelMa  e  cellulhr^Z  lie 
vatchword  of  modern  histology  and  embryology,  and  t  .d  Y 

i.imens  e  nuoleo.     hvery  cell  at  iji-esent  iu  existeucp  mi,-  1,= 
assume.!  to  have  desceuded  from  some  pre WK  exSiu! 
cell  aud  the  nucleus  it  contaius  to  be  a  porlio.  of  the  uuetus 
of  the   aucestral  cell.      New  cells  arise  by  the  divisteu   o' 
previously  ex.stmg  cells,  aud  each  division  of  the  c y  onhsm 
IS  accompanied  by  a  division  of  the  nucleus.     NotCt  that 
under   certaaa    conditions    a  division   of   the   uuc  en      ",' 
occur  without  a  correspoudini;  division  of  tl,.   .,?    >      -^ 
multinucleated  cells  th^s  arisni«,  auHoli"    /idSo™' 
of  the  cytoplasm  may  possibly  in  certain  cases  be  W„ 
rated  «thout  entailing  a  division  of  the  carvoplLm  .  bi' ^^J 
might  be  expected  from  the  relation  which  ext  ,  \T' 
the  Bucleus  and  the  cytoplasm,  the  dM^on  of  he    r" 
is  ..sua  ly  preceded  by  a  division  of  the  caryo  llai  '^   '""''^ 

Ihis  latter  process  may  take  place  in  two  wavs      Tf  ,„„ 
begin  as  a  simple  constriction  of  t le  nucleus  which  b.J        ^ 
deeper  and  deeper,  finally  separates  off  a  po  t  on  o  'i^    7'"'' 
louof  the  cytoph,s.„  iu  asLilarmannerCn  oc«n.t:: 
that  each  of  the  new  cp1I«  fl.,1^  <-.,.       i  .   •     "^^^"^""n.  s>o 

the  original  nucleu:"  tl^^'^X:^:^!^^  1 
|s  rather  rare,  occurs  for  instance  in  e,nb    . '"v  " 

'..anes  of  the  Scorpion  and  is  termed  ^^.-'c;.    '    ,v    •   I"'- 

H.,_towhichtheU..i4m^^.;ir7;:^ 

Hiartiug  with  a  typical  cell,  consisting  of  the  varion^  ,.nvf 
haentioned  .bove,  the   karyolduetic   pheno...   n.  '    .Tbe 
K'u-ded  as  affecting  two  constituenf«  i  n   +i  '  '"''• 

«"M.er  with  the  su.;„,.,,ding'ttTlt  ll    ^r."  '■-r-,  '^ 
j''"ini..  Tlio  centrosome  first  dividpL  ,.'"       -'J- ^^Ucicur  ehro- 

«-iuai,y  separating  fr,,,n^Ur.t;i:.;t'-i"T;:f,::;;:r^ 

I'"'  «t  opp„„te  poles  of  the  nucleus,  ..s„„„;-..:. ^  :;,  l!  ;;;;: 


10 


INVERTEBRATE  MORPHOLOGY. 


tion  ninety  degrees  distant  from  the  point  at  which  the  origin 
nal  ceutrosome  lay.  During  this  process  the  radiating  fila- 
ments which  surround  the  centrosome  become  especially 
distinct  and  may  be  divided  into  two  portions,  those  which 
come  in  contact  with  the  nucleus  and  which  from  their 
appearance  in  later  stages  are  termed  the  spindle-Jibres,  and 


Pig.  2.— Diagram  showing  the  Phenomena  of  Cell-division. 

A,  sL'paratioii  of  tho  ('L-iitiosomt's  niid  aichoplasm;  chromatin  in  skeiu-stage. 

B,  fully  formed  spiudle  ;  chromatin  loops  formed. 
V,  longitudinal  division  of  tlie  clironuitiu  loops. 
2>,  separation  of  chronuitin  loops  and  coninieucenient  of  the  division  of  the 

cytoplasm. 

those  which  radiate  outwards  and  are  lost  in  the  cytoplasmic 
network  and  form  the  aster.  In  the  meantime,  however,  im- 
portant changes  have  been  taking  place  within  the  nucleus. 
The  chromatin  substance,  which  originally  was  scattered  in 
a  reticulum,  begins  to  arrange  itself  in  a  band  (Fig.  2,  A) 
which  with  many  turns  traverses  the  nuclear  substance,  the  | 
nucleoli  which  were  present  at  the  same  time  gradually  van- 
ishing. This  stage  of  the  process  is  termed  the  skein  stage. 
T^i.r.  D>->i»|{llp_fll^i'Qt!  (]f  f.]>o  ppjjf |'{"jR(^n!fi  tlip.n  'ipiif^sir  tn  '•"SPiif^fi'Mf!^ 
through  the  nuclear  membrane,  whicli  sooner  or  later  disap- 
pears, and  by  their  growth  push  the  chromatin  skein  toward-i  I 


the  equator  c 

iug  into  a  ui 

number  of  tl 

cells  of  any  g 

able  variatior 

served  cases  i 

16,  32,  or  to  t 

in  different  fo 

dumbbell-sha; 

less  definite  r: 

this  stage,  wh 

appearance  pi 

(i)  of  the  nuc 

plasm   and   b; 

extending  toAv 

s  )nies  (cr)  lyin 

complex  the  te 


Fig.  2  bis.—Km-y 

Pulgin-  carica. 

Ill  the  next  g 

I  as  a  tyj)ical  shf 

j  V  towards  the  u 

jtliat  there  Avere  ( 

Jl'l.ite,  as  the  re.s 

l^'Uiged  in  2)airs 

'•'  Jiiove  towards 

f'>  ''le  otlier,   sc 

;n>u].  uf  six  chro 

[I'av  be  seen  strel 

pi  ''ippearance  wii 


I'ltOTOl'LASM  AND  THE  CELL.  jj 

the  equator  of  the  nucleus,  the  skein  at  the  same  time  break 
.ng  j„to  a  number  of  fragments,  termed  chroMOso,,es  4t 
number  of  these  chromosomes  is  practically  constant  for  t  I 
cells  of  any  species  of  animal,  and  though  there  is  consider 
able  variation  an  different  species,  yet  in  the  majori  y  of  ol: 
served  cases  the  number  belongs  either  to  the  i-ies  2  4  8 
16,  32,  or  to  that  of  6  12,  24.  They  vary  considerably  in  s  ze 
i^  different  forms,  being  in  some  cases  V-shaped  or  i,(  others 
lumbbell-shaped,  and  arrange  themselves  flnilly  in  a  mo,t  or 
e  s  definite  ring  sui-ronnding  the  equator  of  the  nucler    I 

{")  of  the  nilcleiis  is  a  centosoine  «        ""      .^^  ""''  ''"'^ 
plasm  and  by  the  astrll  ,!  i^  «"'™"''tled  by  archo- 

e^teudiug  to^/ardt^rim    ;  t^^X,  '^T'''' 
-mes  (cr)  lying  at  the  equatoi^of  tl  e  rnicleutl  t,  7" 

™mple.  the  term  a,npMa.t.r  is  sometlJeTipUed?  """"" 


as  a  t    ;L;;rlte'\'l';i'  r^''"'""  -""—■"-.  t-  take  this 

fli.-.t  there  were  mil  ,11-  >»"Rlt"'ll"«llv.      Assu.ning 

^Pl-te,  as  fl  e  res"  It         r'  "r  'r''.''™'-"'"'''  ■"  «■«  equatorial 

o  ...ove  towards  one  of 'n         T      T      ""''  '""''  """'  P™eeeds 
■>  ''-  <.tliei    so    W  e       rlr  "'  '™  """'""^^  """'  "'"  ""'«- 


•»W»**ilfl«»* 


12 


IN  VERTEBRA  TE   MORPIIOLOQ  Y. 


cases  at  the  equator  of  tlie  egg  there  is  to  be  seen  on  these 
fibres  a  number  of  darkly  staining  dots  which  may  be  termed 
the  intermediate  bodies  (Fig.  2,  D).  At  about  this  stage  the 
cytophism  begins  to  divide,  the  plane  of  its  division  passing 
through  the  equator  of  the  nucleus,  aud  there  are  thus  formed 
two  cells,  each  containing  a  nucleus  composed  of  six  chromo- 
somes and  a  centrosome.  The  chromosomes  now  begin  to 
become  irregular  in  shape,  they  gradually  fuse  and  are  finally 
scattered  in  the  form  of  a  chromatic  reticulum  through  the 
substance  of  the  nucleus,  which  thus  passes  again  into  the 
resting  stage,  developing  a  new  nuclear  membrane. 

Our  knowledge  of  many  of  the  details  of  karyokinesis  is  yet  imperfect, 
and  especially  is  this  the  ease  with  regard  to  the  mode  in  which  the  cen- 
trosome exerts  its  influence.  It  has  been  regarded  as  a  simple  centre  of 
attraction,  similar  to  the  pole  of  a  magnet,  but  the  spindle-fibres  seem  to 
be  more  than  passive  in  the  phenomena.  A  comparison  of  the  centrosome 
with  an  aggregation  of  microsomes  has  already  been  referred  to,  and  if 
this  idea  be  extended  some  light  may  be  thrown  upon  the  spindle-fibres. 
Tliey  would  then  naturally  be  regarded  as  reticular  fibres,  i.e.  fibres  of 
pliistin  to  which  a  certain  amount  of  contractility  ar'.  extensibility  may  be 
ascribed.  During  the  earlier  stages  of  karyokinesis  their  extensibility  is 
more  manifest,  and  extending  into  the  nucleus  they  compress  its  chromatic 
substance,  the  contractility  manifesting  itself  later  and  determining  the 
migration  of  the  chromatin  loops  or  chromosomes  towards  the  poles  of  the 
nucleus.  Furthermore,  since  the  linin  reticulum  of  the  nucleus  is  probably 
continuous  with  the  plastin  reticulum  of  the  cytoplasm,  it  is  conceivable 
that  the  activities  of  the  centrosomes  may  call  out  in  it  changes  of  contrac- 
tion or  extension  which  may  suffice  to  bring  r.bout  the  characteristic  skein 
formation  of  the  chromatin  and  the  subsequent  fragmentation  of  the  skein 
into  the  chromosomes,  as  well  as  the  formation  of  the  connective  fibres, 
the  intermediate  bodies  upon  these  being  regarded  as  microsome. 

LITERATURE. 

0.  Hertwig.     Die  Zelle  und  die  Oewcbe.     Jena,  1893. 

W.  Flemminpf.     Zellsubstam,  Kern  iiiid  ZcUtlieilinig.     Leipzig,  1882. 

0.  Btitschli.      Untersiu'hiiugcii  iibcr  mikroskapische  Schdume  und  das  Proto- 

pldsma.     Leipzig,  1893. 
C.  Rabl.     Ueber  Zelltheilung.     Morpliolog.  Jahrbuch,  x.  1884. 
G.  Platner.     Beitriige  zur  Kcnntims  dcr  Zelle  und  ihrer  Theilung.    Archiv  fl'ir 

mikrosk.  Anatomie,  xxxiii,  1889. 
M.  Heidenhain.     tlber  Kern  und  Protoplasma.     Leipzig,  1893. 
E.  E.   Ziegler.  Die  Uologische  Bedeuluuy  der  amiloliiichen  KerntJieilung  im 

Tkierrcich.     Biolog.  Ceutralbl.,  ix.  1891. 


A  8IMI 

power  of 

queutly  tl 

Such    org 

number  oj 

iug  to   a 

grouped   1 

termed   P: 

show  but 

majority  o 

upon  then 

this  physi 

moditicatic 

ous  forms 

permanent 

and  even 

absorption 

horny,  cah 

])rotective  i 

high  degrei 

lular  organ 

various  poi 

For  the  mo 

they  associ 

the  colonie 

functions  o 

labor  amon 

exists  is  in 

«neli  as  Vol 

entiation  ;  n 

identical  pi 


SUDKINGDOM  PROTOZOA. 


la 


CHAPTER  II. 

SUBKINGDOM  PROTOZOA. 

A  SIMPLE  cell,  as  has  already  been  stated,  possesses  the- 
power  of  performing  all  the    fuDctions  of  life,    and   conse- 
quently the  existence   of   unicellular   organisms  is  possible. 
Such    organisms,   together  with  those   which    consist   of  a. 
number  of  cells  grouped  together,  each  cell,  however,  retain- 
ing to   a   greater  or   less  extent   its   own   individuality,  ara 
grouped    together  in    a    subkingdom    and    are    collectively 
termed   Pkotozoa.      In  its  simplest  form  a  Protozoon  may 
show  but  littlo  ditferentiation  of  its  protoplasm,  but  in  the 
majority  of  cases  various  portions  of  the  cell-substance  take 
upon  themselves  special  functions,  and  in  accordance  with 
this  physiological  differentiation  undergo  various  structural 
modifications.     Locomotor  and  prehensile  structures  of  vari- 
ous forms  may  be  developed,  excretory  pulsating  vacuoles,  a 
permanent  mouth    and   pharynx,  special   contractile   bands, 
and  even   pigment  spots   presumably  connected   with   light 
absorption  may  occur,  and  in  addition  the  power  of  secreting 
horny,  calcareous,  or  siliceous  skeletons,  serving  either   as 
protective  or  supportive  structures,  is  frequently  present.     A 
high  degree  of  complexity  may  therefore  occur  in  a  unicel- 
lular organism,  a  complexity  produced  by  a  differentiation  of' 
various  portions  of  the  protoplasm  composing  the  individual,  j 
For  the  most  part  the  organisms  are  simple,  but  occasionally 
they  associate  together  to  form  colonies.     The  individuals  of 
the  colonies  are  as  a  rule  all  alike,  each  carrying  on  all  the 
functions  of  existence  for  itself,  and  there  is  no  division  of 
labor  among  the  various  individuals.     The  complexity  which 
exists  is  individual  and  not  colonial.     A  few  forms,  however, 
such  as  Volvox,  do  present  a  certain  amount  of  colonial  differ- 
entiation ;  all  the  cells  composing  the  colony  are  not  perfectly 
Identical   physiologically,  some  becoming,  ''for  instance,  spe- 


w 


14 


INVERTEBRATE  MORPHOLOGY. 


cialized  for  reproductive  purposes,  while  the  rest  take  but 
little  part  in  this  process.  Such  a  colony  presents  indica- 
tions of  a  passage  towards  a  higher  grade  of  individuality, 
some  of  the  various  cell-individuals  merging  to  a  certain  ex- 
tent their  individualities  in  that  of  the  entire  colony,  and 
becoming  somewhat  dependent  for  existence  on  the  coopera- 
tion of  their  fellows.  This  dependence,  however,  never 
reaches  a  high  degree  of  development  in  the  Protozoa  and  is 
for  the  most  part  entirely  absent.  It  is  in  this  respect  that 
colonial  Protozoa  differ  from  the  higher  organisms,  but  th,^ 
difference  is  one  of  degree,  not  of  kind. 

Four  well-marked  classes  may  be  distinguished  nniong 
the  Protozoa : 

I.  CI.  Bhizopoda. 
II.  CI.  Sporozoa. 

III.  CI.  riagellata. 

IV.  CI.  Infusoria. 

I.  Class  Bhizopoda. 

The  simplest  Ehizopods  present  an  approach  to  the  least 
complicated  condition  under  which  protoplasm  is  known  to 
us.  They  are  simply  small  masses  of  protoplasm,  more  or 
less  granular  towards  the  centre,  clearer  towards  the  periph- 


cv 


Fig.  %.—Anmha  proteus  (after  Gruber). 
w  =  co.'ilractile  vacuole.  n  =  nucleus.  ps  =  pseudopodium. 

try,  and  continually  alter  their  shape  by  pushing  out  lobe- 
or  thread-like   processes  known  as  paeiuiopvdia  (Fig,  3,  ps). 


By  throT 

were,  loc 

genus  of 

gulfed  by 

in  coutac 

food-subs 

iutracellu 

part  of  th 

the  geuer 

pie  proces 

It  is  1 

this;  even 

of  the  pre 

absent  in  j 

ferentiatio: 

and  the  c( 

noticed  in 

the  cell,  a 

even  in  th 

covered,     j 

which  has 

and  that  ii 

been   undii 

I  exists  is  qu 

iu  its  fund 

solution  ace 

protoplasm 

jcal  contraci 

jexpelled  fro 

Various 

jthe  Rhizopc 

[degree  of  di; 

Ireproductioi 

Iteristics  ma-i 


The  For 
^lass.  In  tL 
the  simple  c 


BUBKISODOM  PltOTOZOA.  25 

By  throwing  out  such  a  proocr.s  aud  iiowiug  after  it    as  it 
wero,  locomoliou  is  performed,   wliicl.    fro.,,    a  wel  i,„ 
gem,,  of  the  c1u.b  is  termed  am^ioid.     F^d  i,  sI,ll,T 
gulfed  by  the  protoplasm  flowing  around  it,  at    it  .^r  io,  fe" 

n  contact  w.th  a  pseudopodium,  and  the   digest  m    of 
food.substance  takes  place  within  the  protopla™    ?"      .. 
intracellular.      Undigestible    material'  i^cCcardeda^I 
part  of  the  body ;  respiration  and  excretion  a  ecttdlnW 

he  general  surface;  and  reproduction  is  limited  toihe  "im 
pie  process  of  division.  ®^™" 

i::  raTrhetfrn-s  -LI  z  T'Z  ^^rB 

Wiations  most  usually  oec„rrinra:e%he'i:c:;^^^^^^^ 
the  cell,  and  it'is  quesfion  bt  w     t     firL"Zn  "'T  '^ 

been   undifferentiated,  but  whether  sue  fa  r"  '^  ^"^ 

exists  is  questionable     The  0™^,-!^^!  ,  '"?''"■'""  '"'»' 

ia  its  function,  fluid  contl  ^'^tlXT  meTab"r"'°'^' 
solution  accumulating  at  one  or  mo,-!  r«   •?    ""^ '*''°''™'  '" 

1.  Ordei'  Foramlnifera. 

»Ias^'^!T'"'"""'^"™'''"'^  "'^  «»"Pl'='-  "embers  of  the 

Liass.     In  the  genus  Amrphn  m\,^  q\  •  ^^  "^  i-ne 

tlio  «,-aiple  c]i.r~-f  1        ^     ?•  ^""'^  organisms  presenting 

.-mple  chaiucters  above  alluded  to,  being  simple  naked 


T 


16 


JN VERTEBRA TE  MORPHOLOG  T. 


XJ^K 


Fig.  4. — Arcella  mitrata 

(after  Leiuy) 


masses  of  protoplasm  coutaiuiDg  a  nucleuf?  and  a  contractile 
vesicle  and  presenting  a  slight  differentiation  into  a  peripheral 
more  transparent  ectoplasm  and  a  central  more  granular 
eiidoplasm  in  which  the  nucleus  is  imbedded.  The  pseudo- 
podia  are  as  a  rule  blunt  loV)ose  processes,  though  in  some 

species  they  are  more  or  less  fila- 
mentous and  may  even  be  some- 
what permanent.  The  majority  of 
forms,  however,  secrete  a  protective 
shell  of  varyiiig  composition  and 
com]^lexity.  In  Arcella  (Fig.  4)  it 
is  chitinous  and  smooth,  and  len- 
ticular in  shape,  completely  sur- 
rounding the  protoplasm,  the  pseu- 
dopodia  projecting  from  the  cir- 
cular opening  on  the  flat  surface ; 
in  Eughjpha  it  is  similar  in  composition,  but  sculptured  on 
the  convex  surface  ;  in  Dijffugia  the  shell  is  flask-shaped  and 
composed  of  particles  of  sand  and  similar  foreign  bodies 
cemented  together,  while  in  a  large  number  of  forms,  es- 
pecially those  which  are  marine  in  habitat,  the  shell  is 
calcareous  in  composition. 

It  is  in  these  forms  with  calcareous  shells  that  the  great- 
est complexity  of  structure  occurs.  In  some,  such  as  Gromia, 
the  shell  is  simple  and  flask  shaped,  the  protoi'lasm  pro- 
truding from  the  mouth  of  the  shell  and  covering  its  entire 
surface  as  a  delicate  layer,  from  whi'*h  ilie  long,  slender,  and 
fre([uently  anastomosing  pseud()))odia  take  their  origin.  Al- 
though tlie  ]iseudopodia  are  practically  permanent  in  form 
their  protoplasm  is  continually  changing,  carreuts  streaming 
from  the  body  towards  the  tii)S  of  the  pseudopodia  and  re- 
turning again  to  tlu^  central  mass,  a  constant  circulation  beiii}^ 
thus  maintained,  and  food-] (articles  caught  by  the  delicato 
pseudopodia  conveyed  to  the  central  mass,  there  to  bo  di- 
gested. A  simple  shell  is,  however,  comparatively  raro 
among  these  calcareous  fornis  ,  more  frecpiently  it  consists  of 
several  chambers,  as  in  Miliola,  the  chand)ers  varying  in  size, 
the  first- formed  one  being  the  smallest,  and,  in  addition,  in 
very  many  forms  the  shell  is  perforated  by  minute  pores 


SI 

througli  which  the  p 
chambers  are  arrang( 
as  in  Nodosaria,  som 
axis  as  in  Textularm 
sometimes  as  a  heli 
more  or  less  irreguLn 


■'.■  <■'.■■',  /It 


Fio.  5.—Ro(alii 

Notwithstanding  < 
protoplasm  retains  tl 
and  thougii  in  the  nn 
may  be  replaced  by 
more  marked  differe 
genera. 


In  the  second  on 
slender  as  in  the  ct\]c. 
and  somewhat  rigid, 
being  differentiated  i 
nials  are  usually  glob 
radiating  (uit  from  t 
thus  produced  which 
"sun-animah'uln  "  wh 
such  as  Avtiiiopliri/.s 


SVBKINQDOM  PROTOZOA. 


17 


througli  which  the  pseudopodia  are  emitted.  The  successive 
chambers  are  arranged  in  various  ways,  sometimes  end  to  end 
as  in  Nodosaria,  sometimes  alternately  on  opposite  sides  of  an 
axis  as  in  Textularia,  sometimes  as  a  spiral  as  in  Globigerina 
sometimes  as  a  helix  as  in  liotalia  (Fig.  5),  and  sometimes 
more  or  less  irregularly  as  in  Acervidaria. 


V; 


/.  ■ 


Fk>.  5.— liotalia  venatn  Mftei-M.  Schi-ltzk  from  Hatschek). 

Notwithstanding  the  complexity  of  the  shell,  however,  the 
protoplasm  retains  throughout  tin'  order  its  simple  structures 
and  though  in  the  more  complicatec'l  forms  the  single  nucleus 
may  be  replaced  by  several,  yet  beyond  this  they  present  no 
more  marked  difl'erontiation  than  is  found  in  the  simpler 
genera. 

C.  Order  Heliozoa. 

In  the  second  order,  the  Heliozoa,  the  pseudopodia  are 
slender  as  in  the  ciilcart ous  Foraminifera  and  are  permanent 
and  somewhat  rigid,  the  central  i)r(>t()plasm  of  each  one 
b<'ing  diti'erentiated  into  an  elastic  axial  su])port.  The  ani- 
mals are  usually  globular  in  siiape,  the  slender  i)seud()p()dia 
radiating  (mt  from  the  ccMitral  mass,  an  appearance  being 
thus  produ(^ed  which  is  sullicient  oiuse  for  the  ]»npular  term 
"sun-animah'uln"  which  is  applied  to  several  cf  the  genera, 
such  as  AdiHophnjs  and  AvtiiiosftjKvrhnn  (Fig.  <!).     Currents 


! 


18 


IN VERTEBBA TE  MOBBUOLOQ  T. 


of  protoplasm  traverse  the  pseudopodia  as  in  the  Foramiuifera 
and  carry  the  food-particles  to  the  body  proper.  This  has  a 
delicate  ectoplasm  and  a  central  endoplasm  which  is  fre- 
quently highly  vacuolated  and  contains  one  or  more  nuclei 


Fig.  Q.—ActinosplMrium  Eiclihornii  (after  Leidy). 
CO  and  cc'  =  contrnctile  vncuoles.  //=  ingested  food, 

^=  fgested  food.  ;w  =  pseiidopodium. 

and  contractile  vacuoles.  In  some  forms  also  a  skeleton  is 
<leveloped ;  it  reaches  its  most  perfect  form  in  the  stalked 
CfnthriiUna,  in  which  it  consists  of  a  delicate  fenestrated 
siliceous  sphere. 

3.  Order  Radiolaria. 

The  Radiolaria  are  exclusively  marine  and  are  the  most 
complicated  of  all  the  lihizopods.  Their  ))seudopodia  re- 
semble closely  those  of  the  Heliozoa,  being  slender  and  pos- 
sessing an  axial  sup})ort.  Tlie  body  varies  in  sha])e  somewhat 
in  accordance  with  the  shni)e  of  the  siliceous  shell  with  which 
almost  all  the  forms  are  ])rovided.  In  those  forms  in  which 
the  shell  is  simplest,  as  in  ThuJitsnicolla  (Fig.  7),  whore  it  is  in 
reality  absent,  the  body  is  si»Iierical  and  is  clearly  ditfereii-  | 
tiated  into  t'vo  regions,  not,  liowever,  corresponding  to  the 
ectoplasm  and  endoplasm  of  (^ther  llhizoijods.     The  centre  of 


the  body : 
firm  chitiij 
contains  uj 
and  in  soe 
of  the  cap 
Foraminift 
pores  thro 


Fig. 

continuous 

this  suppos 

iiess,  is  equ 

Foraniiuifei 

pseuilopodi 

ineuted,  bu 

pseiulopodii 

layers  whic 

are  more  ho 

The  shel 

reaching  a  1 

as   JMiosplu 

Klt)l>e  travel 

is  seen  in  i^^ 


SUBKINGDOM  PROTOZOA. 


1» 


the  body  is  occupied  by  a  spherical  mass  surrounded  by  a 
firm  chitiuous  covering  and  forming  the  central  capsule.  This 
contains  usually  many  nuclei  as  well  as  vacuoles,  oil-globules, 
and  in  some  cases  crystals  and  pigment-granules.  The  wall 
of  the  capsule  is  probably  comparable  to  the  shell  of  the 
Foraminifera,  being  perforated  as  in  those  forms  by  minute 
pores  through  which  the  intracapsular  protoplasm  becomea 

\     \    *  '■      f  I   • 

i  J. ^  7 w#  vfw*!*-'  ft  -  -  .,^.:."- • 


^.M-^ 


Fig.  l.  —  T/tiibisHi-oUapdagica  (afUr  Haeckki,  from  Hatschkk). 

continuous  with  the  extracapsular.  This  latter  portion  on 
this  supposition,  notwithstanding  its  greater  relative  thick- 
ness, is  etpuvalent  to  that  jjortion  of  the  protoplasm  of  the 
Foraminifera  which  is  outside  the  shell  and  from  which  the 
])seutlopodia  arise.  It  is  usually  richly  vacuolated  and  i)ig- 
niented,  but  contains  no  nuclei :  the  axial  supjwrts  of  the 
pseudopodia  traverse  it  and  take  their  origin  from  the  inner 
layers  which  in) mediately  surround  the  central  capsule  and 
are  more  homogeneous  than  the  outer  portions. 

The  shell  is  very  various  in  form  in  the  diflfereut  genera, 
reaching  a  high  degree  of  ditterentiation  in  some  forms,  such 
as  IMiosphwm  (Fig.  8),  where  it  consists  of  a  fenestrated 
^lol.e  traversed  by  )'adiating  spines.  Its  greatest  simplicity 
is  seen  in  Splio'wzuum,  in  whii-h  it  is  represented  by  scattered 


*20 


INVEHTEBRA TE  MORPIIOLOG  7. 


spicules,  while  in  Thalassicolla,  already  alluded  to  (Fig.  7),  it 
is  eutirely  absent.  As  stated,  it  is  usually  siliceous  in  char- 
acter, though  in  Acanfhomelra  it  is  composed  of  a  peculiar 
horny  material  termed  acanthin. 

Scattered  through  the  protoplasm  of  the  Eadiolariaus 
there  are  usually  to  be  seen  numbers  of  small  yellowish 
bodies  long  known  as  the  "yellow  cells."  They  are  not  con- 
stant, however,  individuals  of  any  species  frequently  beiu^' 
destitute  of  them,  a  peculiarity  due  to  the  "  yellow  cells  " 
not  being  really  constituent   parts  of  the  Eadiolarian,  but 


/ 
Fig.  %.—HeUospli(vra  actinota  (after  Hakokkl  from  Hatschkk). 

foreign  bodies,  in  fact  unicellular  plants,  for  which  the  term 
Zooxanthella'  has  been  proposed.  They  cannot  be  consid- 
ered parasites,  since  they  do  not  appear  to  exist  at  the  ex- 
pense of  the  host,  but,  on  the  contrary,  their  presence  seems 
actually  to  be  beneficial.  Mutual  benefits  are  conferred  bv 
the  plant  and  the  Radiolarian,  the  coexistence  constituting 
an  example  of  the  ])henomen()n  known  as  Symlnosis. 

I{eprod,urtion  in  the  lihizopods. — Throughout  all  the  grou)»s 
the  simpk'st  form  of  reproduction,  fiHsioiij  is  prnbably  ])reY:i- 
lent  (Fig.  9),  though  it  is  not  yet  definitely  known  to  occur 


the 


Fig.  7),  it 
in  char- 
peculiar 

iolariaus 
yellowish 
uot  con- 
ly  beiu^' 
V  cells" 
dan,  but 


). 

the  term 
cousid- 
t  the  ex- 
e  seeijis 
3rred  by 
stitutiiii.' 

i  groups 
;o  occur 


aVBKINODOM  PROTOZOA.  '  21 

among  the  Eadiolaria.  lu  the  fresh-water  Foraminifera  and 
Hehozoa  it  is,  however,  the  usual  method  in  genera  both  with 
and  without  shells,  and  it  also  occurs  among  the  marine  Fora 
minifera.  Where  the  shell  is  thin  it  may  be  divided  durin-  the 
process  but  where  it  is  thicker  the  protoplasm  divides  within  it 
one  of  the  individuals  retaining  the  old  shell,  while  the  other 
wanders  forth  and  constructs  a  new  house  for  itself  This  is 
the  case,  for  instance,  in  Arcella,  in  which  the  wanderin-  iudi 


Fig.  9.— Division  of  Amoehn  (n  ter  Schclzk) 


vidual  protrudes  from  the  mouth  of  the  parent  shell  until  it 
Ws^its  new  shell,  only  separating  when  thisT  1^1 

Colonies  produced  by  repeated  divisions  and  the  imper- 

onne'l'rtT  ''  ^'^ '"'"^  ^^  ^^"^^"^^^''  ^'^  occasionally 

med,  but  they  are  simply  aggregations  of  similar  individ- 

-ulH.  no  difterentiation  or  individualization  of  the  colony  as  a 

!,._  oceuiiiiig.     Among  the  fresh-water  lihizopods  this  io 

the  case  with  Micro,ro,ua,  a  shelled  form,  numerl  Ldivid 


^  I 


22 


INVERTEBRATE  MORPHOLOGY. 


uals  of  which  may  remain  iu  connection  with  one  another  by 
means  of  their  profusely-branching  pseudopodia.  Colonies 
n^  Adinophrys  are  also  formed  in  a  similar  manner,  and  among 
the  Radiolaria  the  forms  with  rudimentary  shells — such  as 
Sphcerozoum,  produce,  apparently  by  the  division  of  the  cen- 
tral capsule,  numerous  individuals  which  remain  in  contact. 

A  moditication  of  fission  known  as  budding  or  gemmation 
also  occurs  in  some  forms.  It  differs  from  fission  only  in 
that  the  products  of  the  division  difi'er  in  size,  so  that  it  is 
possible  to  regi.rd  the  larger  individual  as  the  parent  and 
the  one  or  more  smaller  ones  formed  from  it  by  budding  as 
the  progeny.  The  process  is,  however,  fundamentally  the 
same  as  fission  and  is  a  derivative  of  that  process.  In  Arcella 
bud-like  processes  arise  from  the  periphery  of  the  parent 
protoplasm,  separate,  and  assume  amoeboid  movement,  leav- 
ing the  shell  in  an  Amoeba-like  condition,  and  some  marine 
Foraminifera  and  probably  certain  Heliozoa  reproduce  in  a 
similar  manner. 

Spore-formation  also  occurs,  the  parent  protoplasm  break- 
ing up  more  or  less  completely  into  a  number  of  small  por- 
tions termed  spores,  which  later  increase  in  size  and  assume 
the  characters  of  the  parent.  This  process  is  sometimes  pre- 
ceded by  encysfment,  a  phenomenon  not,  however,  in  its  origin 
connected  with  reproduction.  It  is  more  prevalent  among 
fresh-water  than  among  marine  forms,  and  seems  to  have 
been  originally  developed  as  a  protection  from  injurious  ex- 
ternal conditions,  such  as  the  drying  up  of  the  pools  in  which 
the  organisms  live.  When  about  to  encyst,  an  Amoeba,  for 
instance,  withdraws  its  pseudopodia  and  assumes  a  spherical 
shape,  and  then  secretes  a  more  or  less  dense  chitinous  case 
or  cj'st  which  completely  encloses  it.  In  virtue  of  the  resist- 
eut  and  non-conductive  nature  of  the  cyst  the  organism  may, 
while  in  this  state,  suffer  uninjured  prolonged  exposure  to 
conditions  which  would  quickly  entail  the  death  of  the  non- 
encysted  individual,  and  on  the  return  of  favorable  condi- 
tions niay  leave  the  cyst  and  reassume  its  active  life.  Occa- 
sionally,  too,  encystment  may  occur  as  the  result  of  good 
nutrition,  an  individual  which  iui«  engulfed  a  number  of 
diatoms,  for  instance,  secreting  a  cyst  around  itself  witliiu 


which  it  rema 
digested,  whei 
diatom  shells 
Plentiful  n 
under  this  te 
related  to  a  ci 
the  two  proces 
be  associated 
10,  A)  feeds  in 
on  a  stalked  i 
contents  of  tl 


Fig. 

A.  Vampyi 

B.  Vampyi 

them  aside  and 

pied  by  them. 

spores  (Fig.  IC 

becomes  a  new 

Among  the 

most  usual  met 

among  them  in 

some  cases  the 

sular  protoplas 

others  some  of 

others   small  (j 

spores  may  be 

vidual  mayproc 

it  is  easy  to  dc 

spores  or  isospo 


8UBKINGD0M  PROTOZOA. 


33 


which  it  remains  until  the  food-matter  has  been  thoroughly 
digested,  when  the  cyst  is  thrown  off  together  with  the  empty 
diatom  shells  and  the  animal  again  becomes  active. 

Plentiful  nutrition  and  reproduction  by  division  (including 
under  this  term  the  various  modifications  of  fission)  are 
related  to  a  certain  extent,  and  it  is  easy  to  understand  why 
the  two  processes  of  eucystment  and  spore-formation  should 
be  associated  together.  The  Heliozoan  Vampyrella  (Fig. 
10,  A)  feeds  in  its  active  condition  on  diatoms,  and  especially 
on  a  stalked  form,  Gomphonema.  After  having  digested  the 
contents  of  the  diatom  frustules  which  it  engulfs,  it  pushes 


A 
B. 


Fig.  10.— Vampyrella  (from  Haeckel  after  Butschli). 
Vampyrella  feeding  upon  the  stalked  diatom  Gomphonema. 
Vampyrella  encysted  upon  the  stalli  of  the  diatom. 


them  aside  and  encysts  itself  upon  the  stalk  previously  occu- 
pied by  them.  Within  the  cyst  the  animal  divides  into  four 
spores  (Fig.  10,  B),  each  of  wliich  escaping  from  the  cyst 
becomes  a  new  Vampyrella. 

Among  the  Eadiolaria  spore-formation  seems  to  be  the 
most  usual  method  of  reproduction,  and  a  complication  occurs 
among  them  in  that  spores  of  two  kinds  may  be  formed.  In 
Horae  cases  the  spores,  which  are  formed  from  the  intracap- 
sular protoplasm,  are  all  equal  in  size  {isospores),  while  in 
others  some  of  the  spores  may  be  large  {macrospor&'i)  and 
others  small  {microspores).  Both  macrospores  and  micro- 
spores may  be  formed  in  the  same  individual,  or  each  indi- 
vidual may  produce  only  one  of  the  two  forms.  In  such  cases 
It  is  easy  to  determine  whether  one  has  to  do  with  macro- 
spores  or  isospores,  which  closely  resemble  each  other  in  size, 


MMMttMii^ 


24 


INVERTEBRATE  MORPHOLOGY. 


from  the  fact  that  the  isospores  are  spherical  in  shape  and 
each  possesses  a  peculiar  whetstone-like  crystal,  wanting  in 
the  macrospores.  All  the  spores  are  provided  with  siuf>Ie 
whip-like  processes,  flagella,  by  which  they  are  propelled 
through  the  water  when  set  free  from  the  parent. 

The  various  processes  so  far  mentioned  concern  a  single 
individual  ouly  aud  are  therefore  non-sexual,  Sexual  repro- 
tluctiou,  consisting  of  a  fusion  of  two  individuals  (covjugation), 
seems  to  be  a  rather  rare  occurrence  among  the  lihizopods, 
though  it  has  been  observed  preceding  spore-formation  in 
several  instances,  the  fusion  being  probably  the  predisposing 
cause  of  the  spore-formation.  In  the  Foraminiferan  Gromia 
the  production  of  spores  has  been  observed,  and  subsequent 
conjugation  of  some  of  the  spores  occurs,  and  it  seems  exceed- 
ingly probable  that  the  macrospores  and  microspores  of  the 
Eadiolaria  are  sexual  cells,  their  further  development  de- 
pending on  the  conjugation  of  a  micro-  with  a  macrospore, 
but  the  fate  of  these  spores  has  not  as  yet  been  ascertained, 
and  their  conjugation  can  only  be  imagined  from  analogy  w-ith 
other  forms. 

II.  Class  Sfobozoa. 

The  Sporozoa,  which  constitute  the  second  class  of  Proto- 
zoa, are  all  parasitic,  living  in  the  cavities,  cells,  or  tissues  of 
other  animals  and  deriving  their  nutrition  from  their  )i'>«x.s. 
At  present  much  is  lacking  to  an  adequate  knowledge  ^i 
various  members  of  the  group,  but  at  least  three  orders  m 
to  be  recognized. 

1.  Order  Gregarinida. 

The  Gregarinida  include  some  of  the  largest  Sporozoa, 
?ind  are  parasitic  either  in  the  body-cavity,  intestine,  or 
organs  of  various  luvertebrata  (especially  in  Annelids  and 
Tracheata),  or  in  the  cells  especially  of  Vertebrated  Animals, 
these  intracellular  parasites  being  .usually  known  as  the 
Coccidia  in  contradistinction  to  the  former,  the  Gregarinid.i 
proper.  The  members  of  both  groups  show  a  marked  ditfer- 
entiation  of  their  protoplasm  into  ectoplasm  aud  endoplasm, 


I 


a  relatively 

known  to  pi 

many    Greg 

covers  the 

sometimes  d 

tuberculatec 

garinida  she 

what  has  b( 

nida  which  i 

present  the 

of  two  cells, 

of  the  body 

of  ectoplasm 

addition  to  t 

cases  is  fun 

finger-like  pr 

the  animal  to 

it  lives.     Eve 

a  single  nuc] 

lar. 

Reproduc 

in  some  case 

or  gemmatioi 

division  beinf 

formation,  pr 

sumes  a  sphe 

,/eater  portic 

number  of 

jver,  remaini: 

mature  the  s 

have  received 

however,   dev( 

plasmic   conte 

spores  (Fig.  li 

the  formation 

these  crescent 

cases  {Po/'ospi 

seems  to  becoi 

later  elongates 


8UBKINOD0M  PROTOZOA. 


25 


a  relatively  large  nucleus  lying  in  the  latter,  and  none  are 

known  to  possess  pseudopodia.     Indeed  in 

many   Gregarinida    a    well-marked    cuticle 

covers  the  exterior  of  the  body  (Fig.  11), 

sometimes  distinctly  striated  or  occasionally 

tuberculated.     The  Coccidia  and  many  Gre- 
garinida show  little  differentiation  beyond 

what  has  been  mentioned,  but  the  Gregari- 
nida which  inhabit  Tracheate  hosts  usu"ally 
present  the  appearance  of  being  composed 
of  two  cells,  owing  to  the  anterior  portion 
of  the  body  being  separated  by  a  partition 
of  ectoplasm  from  the  posterior  part,  and  in 
addition  to  this  the  anterior  moiety  in  some 
cases  is  furnished  with  hooks,  bristles,  or  ^ 

finger-like  processes  (Fig.  11)  of  use  in  fixing  ^^«-  ^^•-nopl(yrhyn- 
the  animal  to  the  walls  of  the  cavity  in  which      "''"*    oiigncanthus 
it  lives.     Even  in  these  cases,  however,  but      ^^"•^'- '™"'""^- 
a  single  nucleus  is   present   and   the   organism  is   unicellu- 
lar. 

Reproduction  is  carried  on  by  spore-formation,  preceded 
in  some  cases  by  conjugation  (Fig.  12),  but  simple  division 
or  gemmation  is  not  known  to  occur,  apparent  instances  of 
division  being  more  probably  cases  of  conjugation.     In  spore- 
formation,  preceded  or   not  by  conjugation,  the  animal  as- 
sumes  a  spherical  shape  and  forms  a  cyst  about  itself,  the 
..reater  portion  of  the  protoplasm  splitting  up  into  usually 
number  of  nucleated  spores,  a   small  portion  of  it,  how- 
ever, remaining  undivided  {residual  body)  (Fig.  12)      When 
mature  the  spores  are  usually  spindle- or  boat-shap-^d  and 
Jiave  received   the  name  oi  pseudonavicellce.      They  do   not 
however,   develop  directly  into  Gregarines,  but  their  proto ' 
plasmic   contents   break   up  into   2,   8,   or   more   crescentic 
spores  (Fig.  12),  a  residual  body  being  again   formed  as  in 
the  formation  of  pseudonavicella3.      The  further  history  of 
these  crescentic  spores  is  not  thoroughly  known,  but  in  some 
cases  {Po,ospora   from   the   intestine    of  the   lobster)   each 
seems  to  become  converted  into  an  amoeboid  structure  which 
later  elongates  to  an  actively  moving  thread-like  organism 


% 


26 


INVERTEBRATE  MORPHOLOGY. 


the  fseudofilaria,  and  this,  gradually  losing  its  motility,  de- 
velops into  the  adult  form. 


_pm---l^ 


PiQ.  12.— Reprodcction  of  Gregarine  (from  Hertwio). 

1.  Clepaidrina  blattarum  in  coiijugiition;  ck  =  ectosarc,  en  =  eudosarc.cjt  = 
cuticula,  pm  =  anterior  portion,  dm  =  posterior  portion,  n  =  micleus. 

8.  Cysts  in  transformation  into  pseiulonaviceliae;  pn  =  pseudonavicellae: 
rk  =  residual  protoplasm. 

3.  A,  a  pseudonavicella  strongly  magnified;  B,  the  same  divided  into  spores, 
sk;  n  ■■=  nucleus,  rk  =  residual  protoplasm. 

One  of  the  Coceidia,  C,  oviforme,  is  very  common  in  the  liver  of  rabbits 
and  has  also  occasionally  occurred  in  Man.  It  is  found  encysted  in  the 
interior  of  nodules  in  the  liver,  and  the  development  goes  no  further  than 
encystation  in  the  body  of  the  host.  On  escaping  from  the  body,  however, 
each  Coccidium  breaks  up  into  four  spores,  and  the  contents  of  each  sporo 
later  divide  into  two  comet-like  bodies  (sporozoites)  which,  when  swallowed 
by  ix  rabbit,  make  their  way  to  the  liver,  where  they  encyst. 

2.  Order  Myxosporidia. 
The  Myxosporidia  are  found  almost  exclusively  parasitic 


in  Fishes,  af 

in  the  intern 

bladder.     Th 

toplasm,  som 

falling  consid 

enclosed  in  c; 

when  not  so 

amoeboid  mo^ 

entiated  from 

tion  a  large  ni 

Keproduct 

formation  bei 

Myxosporidiui 

Pike  the  prot 

masses  each  ( 

all  of  these  m 

six  nuclei,   foi 

two  portions 

trinucleated   b 

pseudonavicell 

sisting  as  the 

at  the  extremit 

structure  cout? 

ment  which  is 

ure  and  proba 

body  of  a  hos 

thoroughly  knt 

escape  as  amoE 

sporidia. 

In  many  respe^ 
but  the  possibilitj 
plant  nature  must 
lations  have  been  f 
view  which  certain 


The  Sarcosp 
i»  the  muselo- 
of  Mammalia,  1 


SUBKINODOM  PROTOZOA.  27 

iu  Fishes  affecting  principally  the  skin,  but  also  occurring 
in  t  le  internal  organs,  such  as  kidneys,  spleen,  an  '  urinary 
bladder.  Ihey  consist  of  irregularly-shaped  masses  of  pro- 
oplasm,  sometimes  reaching  a  length  0.1  mm.,  but  usually 
falling  considerably  short  of  this  size.  Frequently  they  are 
enclosed  in  cysts  developed  from  the  tissues  of  the  host  but 
when  not  so  enclosed  seem  to  possess  the  power  of  'slow 
amcBboid  movement.  The  endoplasm  is  usually  well  diffeiT 
entiated  from  the  ectoplasm  and  contains  in  the  adult  condi- 
tion  a  large  number  of  minute  nuclei 

Keproduction  by  division  is  not  known  to  occur,  spore- 
formation  being  the  only  method  as  yet   observed.     In  the 
Myxosporidium   occurring   in    the    urinary    bladder  of  the 
Pike  the  protoplasm  breaks  up  into  a  number  of  spherical 
masses  each  containing  a  number  of  nuclei.     The  fate   of 
all  of  these  masses  is  not  known,  but  some,  containing  only 
SIX  nuclei,   form   a  wall  about   themselves  and  divide  into 
wo  portions  each  of  which   contains  three   nuclei.      These 
tnnucleated   bodies  elongate,   develop   a   wall,  and   become 
ixseudonavicella-like   spores,  one   of    the   thre;    nucIeT  per! 
siHting  as  the   spore-nucleus,  while  the   other   two,  situLd 
a   the  extremities  of  the  spore,  seem  to  give  rise  to  a  sac-like 
structure  containing  within  its  interior  a  spirally  rolled  fila 
inent  which  is  emitted  when  the  spore  is  Jubje  Jed  to  pre  1 
re  and  probably  serves  for  the  fixation  of  the  spore  to  the 
hody  of  a  host.     The  further  history  of  the  spores  is  not 
thoroughly  known,  but  it  seems  probable  that  the  contents 
Toridia^^  ^"^^boid  masses  which  develop  into  adult  Myxo- 

In  many  respects  the  Myxosporidia  resemble  closely  the  Grecarinirl. 

but  the  possibility  of  their  being  in  reality  not  of  an  anMbut  of  ; 

ant  nature  must  not  be  overlooked.     By  some  authors  theTr  nearest  re 

^U.ons  have  been  found  in  the  Myxomycetous  and  Chytridiaceous  fu.  li  t 

view  which  certainly  has  not  a  little  to  recommend  it.  ^'"'''^''°"'  ^""S''  '' 

3.  Order  Sarcosporidia. 

i..  '!it'  l""f-T^^'  T'  "^"^  "^r^^^  ^^^^P««--  parasites 
If  M  ^"'^f.^'^f^^^"^  «f  warm-blooded  animals,  especially 
of  Mammalia,  being  found   in  the  interior  of  the  primitive 


28 


INVERTEBRATE  MORPHOLOGY. 


fibrils  of  the  striated  muscles,  whose  contents  they  more  or 
less  destroy. 

They  form  somewhat  elongated  sacs  1-2  mm.  in  length, 
the  wall  of  the  sac  being  formed  of  a  distinct  membrane 
which  has  the  appearance  of  being  covered  with  fine  bristles. 
The  contents  of  the  sac  consist  of  a  protoplasmic  ground- 
substance  in  which  a  large  number  of  nuclei  are  imbedded, 
sometimes  aggregated  into  masses  each  of  which  is  sur- 
rounded by  a  delicate  membrane.  It  seems  probable  that 
these  masses  represent  a  process  of  spore-formation,  but  as 
yet  nothing  is  known  regarding  the  further  development  of 
the  spores. 

4.  Order  Heemosporidia. 

The  HsBmosporidia  are  a  group  of  forms  which  occur  in 
the  blood  of  various  Vertebrates,  one  of  the  most  interesting 
of  them  being  the  cause  of  intermittent  fever  in  Man.  This 
form  occurs  as  an  amoeboid  body  in  the  interior  of  the  blood- 
corpuscles,  causing  these  to  enlarge.  The  growth  of  the 
amoeboid  stage  is  completed  in  forty-eight  hours,  and  the  or- 
ganisms then  divide  into  fifteen  or  twenty  spherical  "  spores  " 
which  pass  out  of  the  corpuscles  into  the  blood-plasma,  enter- 
ing later  new  corpuscles.  This  is  the  history  of  the  form 
which  produces  tertian  ague  ;  the  quotidian  and  quartan 
varieties  of  the  disease  are  produced  by  forms  requiring  re- 
spectively twenty-four  and  seventy-two  hours  for  the  com- 
pletion of  their  life-cycles. 

In  association  with  these  Ilcemamceba  forms  there  also 
occur  sickle-shaped  bodies  termed  Laverania  whose  exact  sig- 
nificance is  not  yet  understood,  and,  furthermore,  there  is 
sometimes  found  free  in  \,he  blood-plasma  a  flagellate  struc- 
ture which  is  probably  a  degeneration  stage  of  the  Ham- 
amceha. 


III.  Class  Flagellata. 

The  Flagellates  are  characterized  by  the  possession  of 
one  or  more  long  filamentous  processes  of  protoplasm,  knovvn 
as  JlageUa,  which,  by  whip-like  movements,  propel  the  organ- 


riatfellum  usus 
iletinite  cutich 


8UBKINGD0M  PROTOZOA. 


29 


isms  through  the  water  in  which  they  live,  and  at  the  same 
time  by  the  production  of  currents  in  the  water  bring  food- 
particles  within  their  reach.  Some  forms  possess  pseudo- 
podia  in  addition  to  the  flagella,  which  are  indeed  simply  at- 
tenuated and  mobile  pseudopodia,  but  the  majority  have  a 
mcxe  or  less  permanent  body-form.  This  in  many  species 
is  accompanied  by  the  formation  at  the  exterior  of  the  body 
of  a  skin  or  cuticle  which  in  some  cases,  as  in  the  Dino- 
flagellata,  may  assume  a  sufficient  density  and  thickness  to 
entitle  it  to  be  termed  a  shell. 


1.  Order  Autoflagellata. 

In  the  Autoflagellata  the  body  is  usually  more  or  less 
oval,  and  while  in  many  forms  it  is  naked  and  capable  of 
changing  form  (Fig.  13,  /I),  yet  in  others  special  cuticular  in- 
vestments may  be  present,  taking  the  form  in  some  cases  of 
a  simple  cuticular  covering,  as  in  Evglena  (Fig.  13,  B),  in 
others  forming  a  stalk  by  which  the  organism 
is  attached  to  a  foreign  body  ;  in  some  forms, 
as  in  Codosiga  (Fig.  13,  C\  a  cuticular  collar 
surrounding  the  base  of  the  flagellum  is  pres- 
W\W  A  ®"*'  ^^^"^®  ^"  others,  such  as  Dinohryon,  a  cup 
^<Y      IS  formed,  within  which  the  organism  lives. 

Usually  but  one  or  two  whip-like  flagella 
are  present,  though  occasionally  a  larger  num- 
ber (6  or  8)  may  occur,  and  in  some  instances 
one  or  more  may  assume  a  firmer  character 
and  serve  for  fixation  of  the  organism.     All 
forms  possess  a  single  nuoleous  and  a  contrac- 
tile vacuole.     In  the    simpler  forms,  such  as 
Monas,  in  which  no  cuticle  is  developed,  no 
special  mouth-orifice  is  present,  though  the  iu- 
^ ,.      gestion  of  food  takes  place  at  a  more  or  less 
ctZT''''    "^^^""'^^^y  localized  region  at  the  base  of  the 
>i^oaos^ga        flagellum,    the   food  -  particles    drawn   to   the 
organism  by  the  currents  established  bv  the 


Fig.  13. 
-I,  Oikomonas 

(after  Butschli). 


(after  Butschli). 


Hatfellum  usually  im]ii 

iletinite  cuticl 

aud 


iiigmg  at  this  point ;  where,  ho 


shell  is  developed  a  definit 


vvever,  a 
mouth  occurs. 


in  s.>me  cases,  as  Euglena  (Fig.  13,  B),  this  leads  int 


o  a 


30 


INVKIiTEBRA  TE  MOKPIIOL 00  T. 


distiuct  tubular  pharynx  projecting  some  distance  into  the  in- 
terior. No  hollow  digestive  tract  is,  iiowever,  present,  but 
the  food-particles,  after  traversing  the  gullet,  are  received 
directly  into  the  proti)i)lasm  of  the  body,  and  are  digested 
there  as  in  Amoeba.  A  localized  egestive  region,  situated 
usually  towards  the  posterior  end  of  the  body,  has  been  as- 
certained to  occur  in  some  species,  but  in  no  instance  is  it  a 
permanent  oritice,  as  is  the  case  with  the  mouth.  In  addition 
to  the  nucleus,  contractile  vacuole,  and  food-particles,  other 
definitely  organized  particles,  such  as  starch-like  granules 
and  pigment-granules,  may  by  imbedded  in  the  protoplasm. 
In  Eiujhna  the  pigment  is  green  and  resembles  plant-chloro- 
l)hyll,  probably  too  possessing  a  similar  function.  A  red 
pigment-spot  (stigma)  is  also  present  in  this  and  other  genera 
at  the  base  of  the  fiagellum  and  is  supposed  to  be  concerned 
in  ]ight-])('rception. 

The  typical  Flagellate  is  a  free-swimming  single  organism, 
but  many  forms  are  fixed,  developing  a  stalk  by  which  they 
are  fastened  to  foreign  bodies  ;  the  stalk  may  be  very  much 
branched,  each  terminal  branch  supporting  an  individual,  the 
-whole  thus  forming  a  colony,  without,  however,  any  differ- 
entiation among  the  individuals.  Free-swimming  colonies 
also  exist,  such  for  example  as  VoJvox,  in  which  a  large 
number  of  individuals  are  grouped  together  to  form  a  spheri- 
cal hollow  cohmy.  Each  individual  contains  chlorophyll- 
granules  and  a  red  stigma,  and  is  i)rovided  with  two  fla- 
gella  by  the  action  of  which  the  entire  colony  is  propelled 
through  the  water  with  a  rotai'y  motion. 

2.  Order  Dinoflagellata. 

The  Dinoflagellata  are  distinguished  from  the  members  of 
the  preceding  order  by  the  almost  general  occurrence  of  a 
rather  dense  shell  comi)osed  of  i)lates  of  a  substance  resem- 
bling closely  vegetable  cellulose.  Some  of  the  forms,  such  an 
Cerniium  (Fig.  14),  ])resent  a  rather  bizzaro  shape  on  account 
of  the  shell  Ix'ing  jtrolongtnl  into  horns,  and  in  the  majority 
the  shell-{)lat('S  are  delicately  sculi)tured,  while  arround  the 
equtttor  of  the  shell  runs  a  furrow,  and  from  an  opening  in 


the  lijie  oj 
])()ssesses  t 
acter,  whil 
row  and  in 
of  a  delicat 
r(>phyll-]ik( 
ably  preseij 
Peculiar  c} 
protoplasm 
of  a  hollow 
Avitliin  it  a 
vx'casion  ni 
and  no  doii 
tion,  resem 
structure  tl 


The  ordi 

NodiJuca    1 

structure  n 

is  almost  gl 

the  flagella 

the  mouth-( 

sessing  an  ( 

like  outer  v 

strands  of  ] 

the    central 

nucleus  and 

<lepressi()n 

gella.     The.". 

one  being  sL 

the    other, 

*'  tentacle  " 

contractile,  s 

relatively  to 

cess    of    the 

'J'liis  struct'.] 


8UDKINGD0M  PltOT07A)A. 


31 


Fig.  H.—CeraUuin  tripos 
(a  combination  of  two  figures 
by  IUttschu). 


the  line  of  the  furrow  two  flii^^elhi  protrude,  oue  of  which 
])ossesses  the  ordiuary  whip-like  char- 
acter,  while  the  other  lies  in  the  fur- 
row and  in  some  eases  has  the  form 
of  a  delicate  undulating  band.  Chlo- 
rophyll-like i)ijfnu>nt  is  almost  iiivari- 
ablj  present,  as  is  also  the  red  sti^nii;i. 
Teculiar  cysts  are  also  i)resent  in  tin; 
protoplasm  of  nnxuy  forms,  consistinj,' 
of  a  hollow  capsule  havinj^  rolled  up 
within  it  a  hollow  thread,  which  on 
occasion  may  be  rapidly  eva^'inated 
and  no  doubt  has  a  protective  func- 
tion, resembling,'  very  closely  in  its 
structure  the  uematocysts  of  the  Cadenterates. 

3.  Order  Cystoflagellata. 

The  order  of  the  Cystoflagellata  includes  only  two  genera 
Nixiihica    nd  LepMwcm.     The  latter  is  a  somewhat  <lisk.like' 
structure  jiearly  2  mm.  in  diameter,  while  Nodiluca  (Fig   15) 
IS  almost  globular  with  a  slight  depression  at  oue  point  where 
the  flagella  are  situated,  and  at  the  botton  of  which  is  situated 
the  mouth-opening.     Noctiluca  has  the  form  of  a  cyst,  pos- 
sessing an  external  thin  membrane-  t 
Hke  outer  wall,  to  which  branching 
strands  of  i)rotoj)lasm  extend  from 
the    central    mass    containing    the 
nucleus  and  lying  slightly  below  the 
depression    which  contains    the  fla- 
Knlhi.     These   are   two  in  number, 
one  being  short  and  whip-like,  while 
tiie    other,    usually    known    as    the 
"tentacle"  (Fig.   i5,  /),  is  a  highly 

contractile,  somewhat  riatt.Miod,  ami    ^"*-   !•'>•— ^'oc<*V«m  miliaru 
•vhitively  to  the  Hagellum,  thick  pro!   ,     .      '*',""•  "^"•^•'">- 
c-ass    of    the    internal    protophis.n.    '  =  ^^■"'"^•'^'         "^-'uclcus. 

t.i ,  u,ii^-j,5e.,eijicii  ill  jAinmUscm^  which  OlLef- 

wise  closely  resemldes  NtKiilKca. 


I 

3 


82 


INVERTEBRATE  MORPUOLOGT. 


Noctiluca  is  of  considerable  physiological  interest,  since  it  is  one  of  the 
forms  to  wliich  the  phosphorescence  of  the  ocean  is  due.  The  cause  of  the 
liglit  and  its  character  are,  however,  as  yet  unknown. 

Reproduction  in  the  Flagellata. — The  most  frequent  method 
of  reproduction  in  all  the  orders  of  the  Flagellates  is  simple 
division,  either  transverse  or  longitudinal.  Encystment,  fol- 
lowed or  not  as  the  case  may  be  by  spore-formation,  is  also 
common,  and  when  accompanied  by  spore-formation  may  be 
preceded  by  the  conjugation  and  fusion  of  two  individuals. 
In  Cercomonas  the  spores  are  exceedingly  abundant  and  small, 
presenting  the  appearance  of  minute  granules  even  under  the 
highest  powers  of  the  microscope,  but  in  other  forms,  as 
Chlamydomonas,  the  spores  are  larger  and  much  fewer  in  num- 
ber, being  only  4  or  8  in  this  particular  case.  An  interesting 
modification  occurs  in  closely-related  species  (Fig.  16),  some 
individuals  of  which  divide  into  a  number  of  small  spores 
{microspores),  while  others  undergo  a  more  restricted  division 
and  give  rise  to  a  few  large  spores  [niacrospores).  The  latter 
develop  directly  into  the  adult  forms,  but  the  microspores 
show  a  tendency  to  conjugate  in  pairs  before  undergoing 
further  development.  This  differentiation  of  two  kinds  of 
spores  is  carried  still  farther  in  other  forms  where  neither 


Fia.  16.— 1.  Phacotus  lenticttlaria ;    3,  Macuosi'ouks  and  Mickosi'okes  op 

TIIK  HAMIfi  Sl-EOIES  (after  Ui^TsiHi.i). 

«cA  =  shell.  n  =  nucleus. 

macro-  nor  microsi)orea  develop  directly  but  further  develop, 
ment  is  contingent  upon  the  conjugation  of  a  micro-  with  a 
mucroHpoio. 


In  this  ] 
certain  celh 
spliere,  enla 
when  they  1 
cells  Avhich 
(laughter  co' 
to  this  a  se 
vidu.'ils  grad 
surface  of  tL 
to  enlarge,  : 
frecpiently,  f 
tliigella ;  tlies 
ova  develop 
tion  with  spt 
colony  do  nc 
tegrate  and  < 
it  is  clear  tL 
eutiation  of 
of  the  consti 
iudividualit}" 

In  NoctilHc< 
occurs  which  p 
ceded  by  tlie  C( 
plasuis  coming 
lii'peiited  divisi 
t likes  place  ace 
tliat  (he  surfac( 
liki'  structures. 
on  tiu!  chanict 
adult  Noctihim 


The  Infu 
Protozoa,  HJK 
tained  by  otl 
izod  by  the  \ 
of  liumorous 
cilia  by  mea 
procured.     I 


SUBKINGDOM   PROTOZOA. 


33 


lu  tills  respect  considerable  interest  attaches  to  Volvox  ; 
certaiu  cells,  usually  those  situated  in  the  posterior  heiiii- 
spliere,  enlarge  and  project  into  the  interior  cavity,  dividing 
when  they  have  reached  their  full  growth  into  a  number  of 
cells  which  arrange  themselves  in  a  hollow  sphere  forming 
daughter  colonies  in  the  interior  of  the  parent.  In  addition 
to  this  a  sexual  process  occurs  ushered  in  by  certain  indi- 
viduals gradually  enlarging,  and  leaving  their  position  at  the 
surface  of  the  colony.  In  the  interior  some  of  them  continue 
to  enlarge,  forming  ova  (macrospores),  while  others  divide 
fie(piently,  forming  packets  of  elongated  cells  furnished  with 
tiagella ;  these  may  be  termed  spermatozoa  (microspores).  The 
ova  develop  into  colonies  similar  to  the  parent  after  conjuga- 
tion  with  spermatozoa.  Since  many  of  the  cells  of  the  parent 
colony  do  not  participate  in  this  reproductive  act,  but  disin- 
tegrate and  die  on  the  development  of  the  daughter  colonies, 
it  is  clear  that  we  have  in  this  form  a  rather  marked  differ- 
entiation of  the  individuals  of  the  colony,  the  individualities 
of  the  constituent  cells  being  to  a  slight  extent  merged  in  the 
individuality  of  the  colony. 

In  Noctiluca  in  addition  to  simple  division  a  process  of  roi)fodui;tioii 
occurs  which  partakes  of  the  character  of  budding.  It  is  apparently  pre- 
coded  l)y  the  conjugation  of  two  individuals,  the  combined  central  proto- 
plasms coming  to  the  surface  of  the  cyst  where  they  form  a  protuberance. 
Repeated  division  of  the  nucleus  into  2,  4,  8,  etc.,  up  to  250  or  juore  now 
tiikes  place  accompanied  by  only  u  partial  division  of  the  protoplasm,  so 
tliat  (he  surface  of  the  protuberance  is  covered  tiy  a  large  number  of  bud- 
like structures.  Eventually  these  separate,  develop  a  Magt!llum,  and  take 
on  the  character  of  motile  spores.  Their  further  developmeut  into  the 
adult  Noctihim  Las,  however,  not  yet  been  followed. 


IV.  Class  Infusoria. 

The  Infusoria  are  the  nii.st  highly  specialized  of  all  the 
Protozoa,  showing  a  ditterentiutioii  of  the  protophism  uiiat- 
tained  by  other  meiiibers  of  the  group.  They  are  character- 
ized by  the  possession  during  the  whole  or  part  of  their  lives 
of  numorous  delicate  short  motile  haii-iike  processes  termed 
vU'nt  by  moans  of  Avhlch  locomotion  is  performed  and  food 
procured.     In  one  of  the  orders  into  which  the  class  may  bo 


34 


IN  VERTEBRA  TE  MORPHOLOQ  Y. 


Jivided,  tlie  Ciliata,  these  structures  are  present  during  the 
iidult  life  of  the  orgauisms,  while  iu  the  other,  the  Suctoria, 
though  preseut  iu  the  jouug  stages  they  are  replaced  later  by 
immovable  processes  of  the  body,  which  extract  the  nourish- 
ment from  the  food-particles  which  come  "nto  contact  with 
them. 

1.  Order  Ciliata. 
The  Ciliata  are  for  the  most  part  free-swimming  organ- 


FiG.  17.— A,  Paramecium;  B,  Stentor  ;  C,  Vwticella  ;  D,  Euplotea. 

ev   =  coiitnictlle  viicuole.  n  =  nucleus. 

m   =  inoutli.  n'  =  uiicrouuclous. 

my  =  iuy()i)!mno.  tr  =  trioliooyst. 

isms,  tlioiujfh  some,  o.ff.  Vortwella  ("PxiJ.  17.  /7\   ndlmra  fr»  fz-krai"" 
b()di«>s  by  means  of  a  stalk,  similar  to  that  found  in  Flagel- 


lates, and  c 

In  these  sti 

case,  of  whi 

site  the  stal 

by  cilia  wh 

tected  by  tl 

free-swimmi 

distributed, 

forms,  Fig, 

some  of  the 

bristles  up< 

Fig.  17,  D). 

A  detini 

situated  fre 

and  leading 

cilia,  thoug] 

{(Mlodon). 

food-particL 

the  body-pr( 

is  a  localize 

definite  ana 

ellates  by  th 

iug  minute  c 

cilia  surrouu 

The  bod. 

tral  part,  an( 

tion.     Pigme 

sist  of  Chloi 

contractile  vi 

ally  single,  t 

genus  Opalin 

are  numerou; 

cleus  may  I 

horseshoe-shi 

^fanfor  (Fig.  ; 

nucleus  there 

found  in  its  ■ 

(nictiun  and  i 

iliU'tuentiatioi 


8UBKINOD0M  PROTOZOA. 


36 


I 


]ate«,  and  colonial  stalked  forms  also  occur  as  in  that  class, 
lu  these  stalked  forms  the  body  is  enveloped  in  a  chitinouJ 
case,  of  which  the  stalk  is  a  prolongation,  the  surface  oppo- 
site the  stalk  being,  however,  left  naked  and  being  surrounded 
by  cilia  which  are  absent  on  the  portions  of  the  body  pro- 
tected by  the  chitiu  {Peritrichous  forms,  Fig.  17,  C).  In  the 
free-swimming  forms,  however,  the  cilia  are  more  universally 
distributed,  covering  either  the  entire  surface  {Holotrichous 
forms,  Fig.  17,  A)  or  else  oje  surface  of  the  flattened  body, 
some  of  them  in  this  case  being  modified  into  stout  movable 
bristles  upon  which  the  animal  creeps  (HypotrichoK^  forms 
Fig.  17,  U). 

A  definitely  localized  mouth-opening  is  always  present, 
situated  frequently  at  the  extremity  of  a  peristomial  groove 
and  leading  into  a  gullet  of  variable  extent,  usually  lined  by 
ciha,  though  sometimes  furnished  with  a  chitinous  support 
(C/nlodon).  There  is,  however,  no  special  digestive  tract  the 
food-particles  after  traversing  the  gullet  being  received  into 
the  body-protoplasm,  where  they  are  digested.  Usually  there 
IS  a  localized  cgestive  region,  and  in  a  few  cases  there  is  a 
definite  anal  opening.  The  food  is  procured  as  in  the  Flag- 
ellates by  th.  ^urrents  set  up  in  the  water  by  the  cilia  carry- 
ing minute  organisms  to  the  neighborhood  of  the  mouth,  the 
cilia  surrounding  this  opening  directing  them  to  the  gullet. 

The  body-protoplasm  is  usually  very  granular  in  its  cen- 
tral part,  and  filled  with  food-vacuoles  and  products  of  diges- 
tion.    Pigment-granules  are  sometimes  present  and  may  con- 
sist  of  Chlorophyll,  as  in  Stentor,  and  one  or  more  excretory 
contractile  vacuoles  are  always  present.     The  nucleus  is  usu- 
ally single,  though  occasionally  two  are  present,  and  in  the 
genus  Opalina,  which  occurs  in  the  intestine  of  the  Frog,  they 
are  numerous  in  the  adult  condition.     When  single  the  nu- 
cleus may   bo  very  large   and  either  spherical,   elongated, 
iiorseshoe-shaped  as  in  Vorficelhi  (Fig.  17,  r),  moniliform  as  in 
6tcntor  (Fig.  17,  B),  or  otherwise  shaped.     In  addition  to  the 
iHicleus  there  are  one  or  two  minute  structures  usually  to  be 
found  in  its  vicinity  which  play  an  important  part  in  repro- 
(mctii)n  and  are  known  as  micronndci  {Fiir.  17,  y/,  n').     Other 
ilillerentiations  of  the  protoplasm  are  also  found  in  certain 


UtiSiilif'imtSKn 


36 


INVERTEBRATE  MORPHOLOGY. 


forms,  as,  for  instance,  special  bands  differentiated  so  as  to  be 
specially  contractile  and  therefore  corresponding  in  function 
to  the  muscles  of  the  higher  animals,  and  hence  termed  onyo- 
phanes.  In  Vorticella  a  more  striking  differentiation  of  spe- 
cially contractile  protoplasm  occurs  (Fig.  17,  C,  my) ;  running 
in  an  open  spiral  through  the  centre  of  the  supporting  stalk 
of  this  organism  is  a  strong  ^yopha7ie  terminating  above  in 
the  protoplasm  of  the  c  ^  •  '  When  the  latter  is  stimulated 
the  myophane  contract: ,  .ng  the  stalk  into  a  close  spiral 
and  withdrawing  the  animui  from  the  source  of  irritation.  In 
some  of  the  Holotricha,  such  as  Paramoecium,  numerous  mi- 
nute rod-like  structures  occur  imbedded  in  the  protoplasm 
near  the  surface  of  the  body  (Fig.  17,  A,  tr).  They  are  appar- 
ently defensive  in  function,  since  when  stimulated  they  sud- 
denly, as  if  by  an  explosive  action,  become  transformed  into 
long  threads  or  needle-like  structures  projecting  beyond  the 
cilia.     These  trichocy.^ts  also  occur  in  some  Flagellates. 

2.  Order  Suctoria. 

The  Suctoria  lack  the  active   movements  of  the  Ciliata, 
being  destitute  in  the  adult  stage  of  cilia,  and 
many  of  the  forms,  o.g.  Acineta  (Fig.  18),  are 
attached  to  foreign  bodies  by  a  stalk.     They 
do  not  possess  any  mouth,  but  a  number  of 
simple  or  branched  {Demlrocometes)  saff  pro- 
cesses project  from  the  body  which  serve  for 
the   prehension  of   the  organisms,  principally 
AuKebio,  upon  Avhich  they  feed.     A  contractile 
vacuole  and  nucleus  are  always  present,  the 
nucleus  having  sometimes  a  very  complicated 
shajje.     It  seems  pretty  clear  that  they  have 
been  derived  from   the  Ciliata,  since  in  their 
young  stages  they  are  free-swimming  ciliated 
sti'uctures;  the  tentacular  processes  have  been 
compared  to  the  pseudopodia  of   the   Rhizo-  fio.  \%.'—AcinetM 
pods,  but  good  reasons  for  such  an  homology     gramiis  (after 
do  not  exist,  and.  it  is  more  probable  that  thev      saville  kknt). 
are  structures  ])eculiar  to  the  group. 

The  JicproducfioH  of  the  Jnfmoria. — In  the  Infusoria  tho 


re])roductive 

cation  than  ( 

cesses   of  fis 

former  occui 

mode  of  repi 

e  rations.     L 

many  cases 

unless  the  pi 

Encystme 

under  variou 

has   been  m( 

not  be  follow 

a  resting  cys 

resistent  so  , 

insufficient  a< 

ciated  with  ei 

tiou.     The  di 

closed,  and  ■« 

or  four  parts. 

within  whicL 

gradually  grc 

it  contracts  t( 

Olid  cyst  wit] 

animal  from 

fractive   bodii 

bnrsting  of  th 

in  which  they 

develop.     Los 

amoeboid;    th 

which  elougat 

liliizopod  to  t 

withdrawn,  ci 

the  adult  form 

has  been  obs' 

taL'hes  to  it  as 

!  Infusoria. 

Conjugatio] 

'here  it  suems 


SVBKINGDOM  PROTOZOA. 


37 


reproductive  processes  reach  a  much  higher  grade  of  compli. 
outiou  than  occurs  iu  other  Protozoa,  though  the  simple  pro- 
cesses of  fission  and  spore-formation  likewise  occur  The 
former  occurs  in  the  majority  of  forms,  and  may  be  tlie  only 
mode  of  reproduction  occurring  throughout  a  number  of  gen- 
eiations.  Long-continued  fission  seems,  however,  to  lead  in 
many  cases  to  structural  and  physiological  derangements 
nuless  the  process  of  conjugation  be  interposed. 

Encystment  is  also  of  frequent  occurrence  and  may  occur 
under  various  conditions.     In  Colpoda,  in  which  the  process 
has   been  most  thoroughly  studied,  encystment  may  or  may 
not  be  followed  by  reproduction.     In  the  latter  case'  the  cyst 
a  restmg  cyst,  is  perfectly  closed,  and  the  walls  are  thick  and 
resistent  so  as  to  withstand  unfavorable  conditions,  such  as 
insufficient  aeration  or  dryness.     When  reproduction'  is  asso- 
ciated  with  encystment  it  may  be  either  fission  or  spore-forma 
tiou.     The  division  cyst  is  thin-walled  and  is  not  completely 
closed,  and  within  it  the  animal  undergoes  division  into  two 
or  our  parts.     In  spore-formation  a  thin  cyst  is  first  formed 
within  which  the  animal  slowly  rotates,  at  the  same  time 
gradually  growing  smaller  by  the  expulsion  of  fluid.     Finally 
it  contracts  to  a  round  mass  and  surrounds  itself  with  a  sec 
ond  cyst  within  the  first.     At  the  surface  of   the  encysted 
amnial  from  eight  to  thirty  minute  spherical  and  highly  re- 
ructive   bodies   appear  which   are   the   spores,   an.l    by'  the 
burHtm    of  the  cyst  they,  with  the  remains  of  the  protoplasm 
in  which  they  arose,  escape  to  the  exterior  and  soon  begin  to 
deve  ojx     Losing   its   spherical   shape   each    spore  becomes 
.uncBboid ;    then,  drawing  in  all  the   pseudopodia   Init   one 
V  nch  elongates  and  becomes  a  flagellum,  it  passes  from  the 
K    .opod  to  the  Flagellate  stage ;  and  finally  \he  flagellum  L 
hdrawn    cilia  appear    and  the  animal  gradually  assumes 
lie  adult  form.     Hpore-development  somewhat  similar  to  this 
ms  been  ob,^   rved  also  in  Vorticella,  and  special  interest  at- 
mZX     ""^  "^'''^'-''^^y  ^"^^i^'ating  the  line  of  descent  of  the 

^       CJoujugation  is  a  frequent  process  among  the  Infusoria, 
lieie  it  seems  lo  have  u  rejuvenating  rather  than  a  strictly 


88 


IN  VEHTEBHA  TE  MOIiPJIOLOG  Y. 


reproductive  function.      If  prevented,   and  fission  goes   ou 
through  a  number  of  generations,  marked  degeneration  en- 
sues ;  while  if  it  be  aUowed,  the  same  number  of  generations 
may  be  produced  without  any  signs  of  degeneration.     Tlio 
process  consists  of  a  renewal  of  the  nuclei  and  micronuclei  of 
the  conjugating  forms,  and  the  process  as  it  occurs  in  Colpid- 
ium  colpoda  may  be  described  thus.     Two  individuals  com<^ 
into  contact  by  tiie  anterior  portions  of  their  body,  actual 
fusion  of  the  two  protoplasms  taking  place  at  the  point  of 
contact.     The  microniicleus  in  each  individual  then  enlarges 
and  divides,  the  two  thus  formed  subsequently  dividing  again, 
so   that   each    of   the    conjugating  individuals  contains  four 
micronuclei  and  oue  nucleus.     One  of  the  four  micronuclei 
ill   each   individual   now  divides,  and   one    of   the    two   thiis 
formed  (the  male  pronucleus)  crosses  over  to  the  other  indi- 
vidual and  unites  with  the  other  product  of  the  division,  the 
female  pronucleus,  there  being  thus  a  mutual  interchange  of 
aiicronuclei.     The  individuals  now  separate  and  resume  their 
independent  existences,  and  a  rearrungement  of  the  nuclear 
structures  accompanied  by  fission  takes   place.     The  three 
micronuclei  which  did  not  take  part  in  the  formation  of  the 
pronuclei  of  conjugation  degenerate,  as  does  also  the  original 


Fig   19.-DIAQUAM  to  Illusthatk  the  Beiiaviou  of  the  Nuclei  and| 

Micronuclei  duuino  Conjugation  in  Infubouia  (after  Maupas). 
nucleus.  The  conjugation  micronucleus,  formed  by  the  fusioul 
of  tho  male  and  female  pronuclei,  divides  twice,  forming  foiuj 
micronuclei,  and  this  is'  followed  by  a  fission  of  the  entirej 
Infusorian,  each  of  the  daughter  forms  so  produced  possessniJ 


two  micronuc 

iiiu'Ieus,  while 

('()iiil)Ii(';ited  I 

accdihpanying 

In  the  mil 

[)rocess,  the  tv 

pioimclei.     In 

J>y  j-epeated  1< 

into  a  number 

land  swim  abo 

('OHIO  into  con 

i])orni;uient  fusi 


I.  Class  Rnizop( 

1.  Order  Fo 

when  p 

(a)  ^ 

(b)  S 
(0)  S 
(d)  g 
(e)S! 

2.  Order  ^cif 
present 

(a)  S 

{b)  SI 

3.  Order  lia( 

usually 

present. 

(a)  SI 

(6)  SI 

(e)  Sh 

II.  Class  Spouozo, 

1.  Order  (Tfre;, 

Invertel 

2.  Order  Jfiji 

internal 

•i.  Order  <SV//y; 

^.  Order  ffiri 

111.  Clnss  Fla(;k!.!. 

1.  Order  AiU< 

vacuola 


suBKiminoM  I'll!)  / -D/j).  [ 


89 


l^vo  nucronuclei.  One  of  these,  enbirgin-  becomes  the  uo^^^ 
nucleus,  while  the  other  remains  us  the  mieronuclens.  Tliis 
.•niuplicatea  process  may  perliaps  be  better  followed  iu  the 
accdihpanying  diagram  (Fig.  19). 

In  the  majority  of  forms  tlie  conjugation  is  a  temporary 
I)n)cess,  the  two  individuals  separating  after  the  exchange  Jf 
l)r()imclei.  In  Vorticdla,  however,  a  permanent  fusion  occurs. 
V>y  repeated  longitudinal  fission  a  Vorficella  becomes  divided 
I  into  a  number  of  small  individuals  which  leave  their  stalks 
and  swim  about  freely  in  the  water.  Should  one  of  them 
(■oiiie  into  contact  with  a  large  individual  a  complete  and 
h)ornianent  fusion  of  the  small  with  the  largo  one  occurs. 

SUBKINGDOM  PKOTOZOA. 
I.  Class  RmzopoDA. -Protozoa  willi  lohe-likoor  filamentous  psoudopodia, 
1.  Onlor  i'T>r«w</«;/era.—P.soud()po(]la  without  axial  support;  sliell 
when  present  liorny  or  calcareous. 

(a)  Siioll  absent.     Ainwha. 

(b)  Shell  horny.     Arcel/a,  Euf//i/pha. 

(c)  Shell  of  foreif,Mi  i)artiolos  cemented  together.     Difflnyia. 

(d)  Siiell  calcareous,  imperfoi-ate.     Qromia. 

(e)  Sliell  calcareous,  perforate.     Miliola,  Nodosaria,   Textu- 

laria,  Globiijerind,  Rofn/a,  Acervularia. 
'i.  Order  /fc-^/o^oa.— Pseudopodia  slender,  with  axial  support;  shell  if 
present  siliceous  ;  no  central  capsule. 
(a)  Shell  wanting.    Actinophrys,  Actinospharium,   Vampy- 

rella,  Mit-ror/rom la. 
(6)  Shell  present.     (Jlathrulim. 
3.  Oraer  iia(^/o/a/7-«.-Pseudopodia  slender  with  axial  support;  shell 
usually  present  and  siliceous   (rarely  horny)  ;  central  capsule 
present. 

{a)  Shell  wanliug.     Thnlasdcolla,  SpJurrozoon. 
(6)  Shell  siliceous.     AcUnomma,  HeUosphwm. 
(c)  Shell  liorny.     Amnthometia. 
n.  Class  SpouozoA.-Parasitic  ;  without  pseudopodia,  flagella  or  cilia 
1.  Order  (i>'e,jari,n<la.--l\xrA?,\VMi  in  cavities  of  the  body  especially  of 

Invertebrates  or  in  the  cells  especially  of  Vertebrates. 
3.  Order  J/y-mv/w/vW/*/,. -Parasitic  usually  in  tiie  skin,  sometimes  in 

interruil  organs  of  fishes. 
:i.  Order  .Sajv.ospnrhlia.  --Parasili,!  in  tli"  muscle-fibres  „f  Mammalia. 

.  (Jrder  Hwmosjm'kJ ia.—V(ivii^\i\Q  in  the  blood  of  Vertebrates 
(  Inss  FLAciKu.ATA,      I'rovided  with  .,ne  or  more  flagella 
1.  Order  Aut.>f1,,,jcllnta.-Wnhunt  shell,   protoplasm  not  especially 
vacuolated.  ^ 


III 


40 


IN  VEllTEBllA TE  MOEPUOLOG  7. 


(a)  Without  coWav.—Monas,   Cercomonas,  Chlamydomonus, 

Eiif/Ieiia,  Volvox. 
(6)  Witli  collar. — Codosiga,  Dinohrijon. 
3.  Order  Dinu/lof/ellaia.— With  shell  composed  of  cellulose.     Cera- 

tium. 
3.  Order  Cysto/lageUata.— Without  shell,  protoplasm  highly  vacuo- 
lated, marine.    Noctilnca,  Leptodiscits. 
IV.  Class  Infusoria.— Provided  with  cilia  or  immovable  processes. 
1.  Order  CZ/m^a. —Provided  with  cilia  in  adult  stage. 

(a)  Cilia  of  nearly  uniform  length  all  over  the  body  {Holo- 
tricha).    Paminoecium,  Colpoda,  Colpidium,  Chilodon, 
Opalina. 
(6)  Cilia  around  anterior  end  of  body  longer  tlian  tne  rest 
{Heterotricha).     Stentor. 

(c)  Cilia  limited  to  anterior  end  of  body  (PeritricJia).    Vorti- 

cella. 

(d)  Cilia  or  setae  only  on  ventral  surface  of  the  body  {Hypo- 
tricha).     Stylonyehia, 

3.  0-der  Suctoria.— With  cilia  only  ir.  the  young  stages,  in  the  adult 
with  immovable  processes.     Fodopliryn,  Acineta. 


LITERATURE. 

0.  Biitschli.  Protozoa.  Bronn'sKlassen  u.  ORimmgendesThierreichs.  Leip- 
zig u.  iI'jiQylberg,  1888-87. 

W.S.Kent.     A  Manual  of  the  lnjumiia.     Lomloii    1880-83. 

J.  Leidy.  Fresh-water  lihizopods  of  North  America.  U.  S.  Geological  Sur- 
vey of  the  Territories,  xii.  1879. 

B.  Hertwig.  Bemerkungen  zar  Organisation  und  systematischen  Stellung  dtr 
Foraminiferen.     Jeuaische  Zaitschr.,  x.  1876. 

E.  Haeckel.     Die  Radlolarien.     Eine  Mon-jgraphie.     Berliu,  1862-88. 

K.  Brandt.  Pie  Kolonie-bildenden  Radiolavien  {Sphmrozoen)  des  Oolfes  von 
Neapd.     Fauua  u.  Flora  des  (iolfes  vou  Neapel.    Mono^rapLie,  xni.  188'). 

A.  Labbe.     Rrxherches  zoologiques  et  hiologiques  .mr  les  parasites  endrglobidaires 

da  sang  des  Vertebris.     Arch,  de  Zool.  Expcr.,  Ser.  3™",  ii.  1894. 

F.  Stein.     Per  Organisnius  der  Infusionsthiere.     Leipzig,  1859-79. 

E.  Maupa.      La  rajeunissement  karyogamique  chez  les  Cities.    Archives  de  Zo(j1. 

experimeutale,  2'""  t^er.  vii.  1889. 
L.  Rhumbler.     Pie    verschiedenen    Cystenbildungen    und  die   Entteicklungsqr- 

schichte  der  holotrichen  Lifmoriengatlung  Colpoda.      Zeitschr.   fur  wis- 

sensch.  Zoologie,  XLVi.  1888. 

B.  Hertwig.      Ueber  Podophrya  gemmipara,   etc.     Morpholog.  .Jahrbuch     • 

1876. 


be  ;  aggregates 


miBKlNGDOM  METAZOA. 


41 


CHAPTER  III. 

SUBKlNGDOx¥  METAZOA. 

The  Metazoa  are  equivalent  to  colonies  of  Protozoa,  the 
mdividual  cells  of  which  have  differentiated  in  various  direc 
tious,  some  being  more  especially  contractile,  others  nutritive' 
othei-s  irritable,  others  reproductive,  etc.,  instead  of  each  one 
for  Itself  performing  equally  all  the  functions  necessary  for 
existence.     A  physiological  division  of  labor  of  a  more  or  less 
perfect  kma  is  introduced  among  the  individuals  composing 
the  colony,  and  the  welfare  of  each  individual   becomes  de 
pendent  upon  the  proper  performance  by  its  colleagues  of 
their  special  functions;  in  short,   the  individualities  of 'the 
component  cells  are  merged  in    the  higher  individuality  of 
the  whole  organism.  ^ 

Physiologically  a  Metazoon  is  equivalent  to  a  Protozoon 
but  morphologically  it  is  the  equivalent  of  a  large  number  of 
them.     Each  IS  physiologically  an  individual,  but  morpholog- 
ically the  Metazoon  is  a  colony  of  Protozoan  individuals     To 
harmonize  the  physiological  and   morphological  conceptions 
0    an  individua    it  is  necessary  to  recognize  several  grades 
of  morphological  individuality  of  which  the  cell   mav  be  -is 
sumed  to  be  the  lowest.     In  the  Metazoa  the  physiologilal 
diffei-entiatK^ns  of  the  cell-individuals  are    accompanied   by 
ti-uctural  differentiations,  so  that  it  is  possible,  as  a  rule  to 
determine  from  its  structure  what  the  function  of  a  cell  mav 
be  ;  aggregates  of  similar  cells  are  termed  tissues  or  tissne-indi- 
Ms,  and  as  the  simplest  Metazoa  are  complexes  of  various 
tissues,  such  a  complex  forms  the  third  grade  of  individu- 
ality and  may  be  termed  an  Organ-individual.     A  complex  of 
organ-individuals  united  to  form  a  physiological  unit  consti- 
utes  an  individual  of  the  third  grade,  the  3Ietamere.indi,idual, 
Awhile  the  fourth  grade,  the  Cormus,  is  formed  bv  a  similar 
umon   of  a  number   of   metameres,  as,   for  instance,   in  the 
l.arthworm,  each  joint  or  segment  of  which  is  a  metameie 


^S^^^lP 


42 


INVEHTEBRA  TE  MOHPHOLOO  Y. 


It  has  been  pointed  out  that  the  FhigelUite  Volvox  presents 
a  tendency  towards  a  higher  individuality,  being  somewhat 
higher  than  a  mere  colony  of  cell-individuals  and  yet  not 
quite  reaching  the  dignity  of  an  organ-individual ;  similarly 
intermediate  conditions  between  the  other  grades  may  occur. 
In  certain  worms,  for  instance,  considerable  independence  of 
the  I  nstituent  metameres  exists,  any  one  of  them,  when  de- 
tached, being  capable  of  carrying  on  an  independent  exist- 
ence, and  of  developing  into  an  organism  similar  to  that  of 
which  it  was  originally  a  part.  In  the  Earthworm  the  depend- 
ence of  the  various  segments  or  metameres  upon  one  another 
is  greater  than  this,  but  in  it,  too,  a  certain  amount  of  inde- 
pendence is  shown  by  the  power  it  possesses  of  regenerating 
lost  metameres.  In  other  cormi,  as,  for  instance,  in  the 
Lobstei",  the  interdependence  of  the  component  metameres 
proceeds  still  farther,  and  a  differentiation  of  the  various  meta- 
meres occurs,  a  process  carried  to  its  greatest  extent  in  the 
higher  Vertebrates.  A  physiological  division  of  labor  amouj^f 
the  metameres  develops,  some  of  them  losing,  for  instance, 
their  excretory  organs,  while  in  others  these  organs  lose  their 
excretory  functions  and  serve  as  ducts  by  which  the  repro- 
ductive elements  may  pass  to  the  exterior.  The  subordina- 
tion of  the  metameres  proceeds  most  rapidly  and  is  most 
complete  at  the  anterior  extremity  of  the  organism,  leadiug 
to  the  formation  of  a  head  bearing  highly  developed  sense- 
organs  and  containing  a  complex  nervous  system,  which  rep- 
resents originally  distinct  metamere  nervous  systems,  now 
fused  and  destitute  of  all  independence. 

Sexual  Iieproducfion  in  the  Metazoa. — In  cell-individuals  it 
has  been  seen  that  fission  is  the  most  frequent  and  simplest 
mode  of  reproduction  ;  in  the  Metazoa  this  method  and  its 
modification,  budding,  also  occurs,  but,  as  a  rule,  only  iu 
forms  of  a  low  grade  of  individuality  or  in  a  transition  stage 
between  a  lower  and  a  higher  grade.  In  organ-individuals 
it  is  of  frequent  occurrence,  the  imj^erfect  separation  of  tlie 
individuals  so  produced  leading,  in  many  cases,  to  the  forma- 
tion of  colonies,  and  in  cormi  in  which  tlie  integration  of  the 
constituent  metameres  is  but  slight  it  also  occurs. 

In  the  Protozoa  cell-division  naturally  entails  reproduc- 


SUBKINGDOM  METAZOA.  43 

tiou,  but  iu  organ-individuals  reproduction  of  the  constitu- 
ent  cell-individuals   is   not   necessarily  connected   Avith    the 
reproduction  of  the  entire  individual,  but  may  simply  increase 
the  number  of  lower-grade  individuals  of  which  it  is  com- 
posed.     Similarly  multiplication  of  the  organ-individuals  of  a 
luetamere,  or  of  the  metamere-individuals  of  a  cormus  may 
occur  without  producing   reproduction  of   the   whole  •    it  is 
snuply  growth.     From  growth  to  reproduction   l,y  budding 
the  path  is  short,  and  various  intermediate  stages  connecting 
the  two  processes  can  be  found.    Hence  reproduction  has  been 
.iptly  dehned  as  "discontinuous  growth,"  though   perhaps  it 
would  be  even  more  apt  to  define  growth  as  reprodiccHon  icith- 
out  discontinuity,   growth  in  a  Metazoon    depending   on    the 
I  reproduction  of  the  lower-grade   individuals   of  which  it  is 
composed. 

It  is  possible  to  carry  this  idoa  still  farther  back  and  refer  the  growth 
of  a  ceil  to  the  reproduction  of  the  constituent  elements,  plasomes,  of  which 
It  .nay  be  miagmed,  it  is  composed.  In  the  simplest  cells  the  various 
onus  of  plasomes  are  distributed  throughout  the  cell,  but  in  the  hLWier 
1  rotozoa,  for  n.stance,  an  aggregation  of  similar  plasomes  occurs,  givin<^ 
nse  to  such  structures  as  the  myophanes.  In  a  similar  manner  h.  th^ 
hmv  Meta.oa,  although  a  division  of  labor  and  structural  differentiation 
has  taken  place  among  the  constituent  cells,  yet  the  cells  possessing  similar 
functions,  as,  for  mstance,  the  nerve-cells,  are  more  or  less  ir^gular  y 
scattered  throughout  the  body,  only  becoming  aggregated  in  the  higher 
fornis  mto  d.stmct  tissues,  and  giving  rise  to  the  most  perfect  type  of  an 

0  Kan-nuhvulual.     Likewise  in  a  metamere-individual  a  multipHcation  o 
le  organs  leads  to  a  transition  form  with  discretely  arranged  parts,  the 

1  hnite  aggregation  of  which  produces  a  cormus,  composed  in  the  sin  pier 
fonns  of  d,s  Hict  metameres,  which  become  more  and  more  integrated  and 

:::;;:!;f:;:;;Udm;r  ^-^^^^^^^^^^^  -' ''-  ---  -  ^^^'-  ^^-  -  ^'^- 

According  to  this  view  the  segmentation  or  metamerism  of  the  higher 
M.'tazoais  the  result  of  the  multiplication  and  subsequent  integration  of 
i>'  organ-.nd.vKluals  of  an  ancestral  metamere-individual,  and  explains 
•IH.  occurrence  of  imperfect  metamerism  in  certai.i  forms  o    that  So 
,  n  u,  ,,in,y  (2W,VW/«nV;).    Some  authors  have  considered  metan.fnl    o 
I    Ji^e  a  men  by   he  reproduction  by  budding  of  an  ancestral  metamero   an 
ea  which  fails  io  explai..«  satisfactorily  the  condition  Just  referred  io 
1  If  view  presented  here  considers  metamerism  to  be  the  result  of  c^rowth' 

"!;"iuj;'"'r"  '7  *"V^^^^'^^-''-  -^  ^'-  '-^amere,  but  by  tlna  of  its 
o'^aiiN  just  as  a  typical  organ-individual  has  arisen  by  the  reproduction 
and  integration  of  its  constituent  cell-individuals.  louuction 


i 

c 

i 

2 


44 


IN VEliTEBRA  TE  MORPIIOLOQ  Y. 


As  a  mode  of  reproduction  iu  tlie  Metazoa  division  plays 
but  a  secondary  part,  the  sexual  process  being  the  character- 
istic method.  Attention  has  already  been  called  to  the  par- 
tial specialization  in  Volvox  of  reproductive  cells  Avhich  servo 
to  perpetuate  the  species,  the  remaining  cells  of  the  colony 
perishing.  This  condition  is  a  premonition  of  the  more  per- 
fect specialization  found  in  the  Metazoa  of  reproductive  or  gervt 
cells  and  non-reproductive  or  somatic  cells,  the  hitter  serving 
for  the  nutrition  and  protection  of  the  germ-cells,  t(;  whicli 
the  perpetuation  of  the  species  is  entrusted.  Comparatively 
early  in  the  development  of  an  individual  certain  cells  differ- 
entiate from  the  others,  not  undergoing  like  them  a  physi- 
ological and  structural  specialization,  but  retaining  a  general- 
ized character.  Tliese  are  the  germ-cells  usually  grouped 
together  to  form  the  reproductive  orgaus. 

In  describing  the  methods  of  reproduction  occurring  in  the 
riagellata,  the  manner  of  the  development  of  sexual  repro- 
duction was  indicated.  It  appears  to  have  been  originally  a 
more  or  less  accidental  fusion  of  two  similar  cells  or  spores, 
and  from  being  accidental  this  fusion  gradually  became  the 
rule  on  account  of  the  greater  vitality  which  the  conjugate  in- 
dividual possessed  over  cells  which  did  not  conjugate.  The 
next  step  was  the  differentiation  of  microspores  and  macro- 
sjiores,  which  reaches  a  high  development  in  J^tJi'Ojr,  where 
it  is  associated  also  with  a  differentiation  into  somatic  and 
germ  cells.  In  the  Metazoa  both  these  differentiations  are 
carried  to  a  higher  degree,  the  macrospores  being  known 
as  ovd  and  the  microspores  as  sperm<itozo<i,  while  the  aggre- 
gates of  these  cells  are  termed  respectively  ovaries  and  icsten. 

In  a  young  embryo  a  mass  of  germ-cells  which  is  to  gi\o 
rise  to  spermatozoa  cannot  be  distinguished  from  one  which 
is  destined  to  be  converted  into  ova.  Fundamentally  both 
are  the  same,  and  occasionally  a  portion  of  a  mass  of  genu- 
cells  may  be  differentiated  into  ova,  while  the  rest  of  it  devel- 
()])s  into  s}»ormat()Zoa.  This  has  not  unfre(iuently  been  seen 
in  fishes  in  which  there  is  normally  a  separation  of  the  sexual 
elements  iu  distinct  individuals,  and  throws  considerable 
light  upon  the  occurrence  of  forn)s  which  normally  ])oss('>is 
both  elements.     This  ct)ndition  of  livrttiaphi'oditism,  which  oo- 


SUBKINGDOM  METAZOA. 


45 


(Ills  iu  many  pcarasitie  forms  and  in  certain  sponges,  Flat- 
Avorms,  Mollusks,  and  Crustacea,  seems  to  have  been  second- 
iivily  acquired.  It  is  probable  that  the  ancestral  Metazoa 
were  unisexual,  possessing  reproductive  elements  of  only  one 
kind,  a  supposition  borne  out  by  the  frequent  association  of 
liermaphroditism  with  a  parasitic  or  sessile  mode  of  life,  such 
conditions  being  what  may  be  termed  abnormal,  and  usually 
accompanied  by  marked  structural  characters  which  are  to 
1).'  regarded  as  secondary  modifications.  On  the  other  hand, 
it  is  noticeable  that  the  lowest  free  Metazoa  (such  as  the  free' 
swimming  Cnidaria)  are  unisexual. 

An  ovum  is  a  single  cell,  and  iu  its  typical  form  ccmsists 
of  a  mass  of  protoplasm  containing  a  nucleus,  and  may  or 
may    not    be    surrounded    by    a    membrane. 
Seldom,  however,  does  such    a   simple  ovum 
occur;   usually  more  or  less  yolk,  consisting  ^  « 

of  fatty  and  albuminous  globules,  is  distrib- 
uted throughout  the  protoplasm,  and  fre- 
(jiiently  the  amount  of  yolk  far  overbalances 
the  amount  of  protoplasm.  Other  structures, 
such  as  albumen  and  one  or  more  enveloping 
ineinbranes,  may  be  added,  the  ova  of  different 
sj.ecicis  differing  greatly  iu  this  respect. 
Among  the  lower  forms  th«^  ova   are  usually 

extruded  freely  from  the  body  of  the  parent, 

hut  in  many  of  the  higher  Metazoa  they  are 

eiu;U)sed  Avithiu  protective  cas'^s  (cocoons),  as 

in  the    Earthworm,  or  imbedded  in  jelly-like 

masses,  as  in  the  common  Pond-snails. 

In  the  ovary  of  a  young  individual  all  the  Pru  2().-Ovahial 

germ-cells  are  alike,  and    all    are    pottuitially     'I'l'i'i-:  ok  a  Mkk- 

reproductive    colls;  very  fre(iuently,  however, 

many  of  the    p'iniitive   genii-c(Uls    relimiuish 

their  reproductive  function  and  serve  as  pur- 

veyors  of    nutrition    to   certain  of  their  com- 

liidos  which  enlarge  and  bcconu^  mature  ova.   .'/ =  yolkcdlH. 

This  is  well  seen  in  insects,  in  which  each  ovary  '^  "  f"'"it'l<'fiH8. 

(iMg.  20)  consists  of  a  number  of  tubes  tapering  to  a  point  at 

one  end,  while  at  the  other  they  open  into  u  common  duct, 


i)xfT. 


I.ni 


Ti,|.;     (ufi.T 

IIOCK). 

g  —  ^(Miiiiiml    re 

0  —  OVIl,  Ijk'ioM. 

«  ^^miiluu'  ovmii. 


t 


46 


INVERTEBltA TE  MOltPIIOLOG  Y. 


the  oviduct,  leading  to  the  exterior.  At  the  tip  of  each  tube 
the  primitive  germ-cells  (Fig.  20,  g)  are  located,  and  lower 
•down  ova  (o)  in  various  stages  of  development  towards  matu- 
rity are  to  be  found,  each  surrounded  by  a  number  of  small 
undeveloped  germ-cells,  known  as  follicle-cells  (/),  whose  func- 
tion it  is  to  transfer  food-yolk  (y)  to  the  growing  ovum.  As 
the  latter  approaches  maturity  the  follicle-cells  secrete  around 
it  a  thick,  sometimes  highly  sculptured  shell  and  finally 
degenerate. 

As  a  rule,  conjugation  with  a  spermatozoon,  i.e.  fertiliza- 
tion, is  necessary  as  an  antecedent  to  further  development. 
Before  this  takes  place,  however,  certain  modifications  of  the 
ovum  are  necessary,  the  phenomena  which  accompany  them 
being  known  as  the  mat  unit  ion  of  the  ovum.     In  this  process 


PS- 


A  B 

FlO.   vl.— DlAORAMR   ILLUSTUATING   TIIK   MaTUUATION   OF  THF:   OVUM. 

A  =  foriimtiou  of  the  liisl  poliir  globule  (pff). 

li  -  foimiitioii  of  the  second  polar  globule  iind  eiilianct'  of  the  spenn-iiuclcus 

(Fig.  21,  A)  the  nucleus  ai^proaches  the  surface  of  the  ovun) 
and  there  undergoes  u  karyokiuetic  division  which  is  pecnljjir 
in  that  iii  the  e(iuat()rial-i)liit(^  stage  twice  as  many  chronio- 
souios  are  foruied  as  are  typical  for  the  species.  Thes<>  do  not 
undergo  longitudinal  division,  and  by  tlie  karyokinesis  th(>ir 
number  is  reduced  to  the  typical  number,  a  small  cell,  the 
polar  (jlooule  ( pg),  being  separated  from  the  ovum  with  half 
the  chromosoiues,  whih^  the  others  are  retained  within  the 
ovum.  The  nucleus  of  the  t)vum,  instead  of  now  returning 
t..  tin,  resting  stage,  divides  again  iFig.  21,  //),  a  second  polar 
globule  being  formed    and    receiving  half  (he  chroniosimies 


SUBKINGDOM  METAZOA.  47 

whicli  remain,  so  that  the  nucleus  of  the  ovum  now  possesses 
oiilj  half  the  number  of  chromosomes  which  are  character- 
istic  for  the  species.  At  the  time  of  the  formation  of  the 
second  polar  globule  the  hrst  frequently  divides  without  its 
uuclsus  passing  into  a  resting  stage,  so  that  as  the  result  of 
this  maturation  process  four  cells  have  been  formed,  three  of 
which  are  small,  while  the  third  is  relatively  very  large  and 
will  alone  undergo  further  development.  AVhen  these  divi- 
sious  have  been  completed  and  the  chromosomes  have  been 
reduced  to  one-half  their  proper  number  the  nucleus  of  the 
ovum  passes  into  the  resting  stage,  migrates  back  towanls 
the  centre  of  the  ovum,  and  is  ready  for  conjugation  with  the 
nucleus  of  a  spern)atozoon. 

The  spermatozoa  are  always  much  smaller  than  the  ova, 
and  are,  as  a  rule,  capable  of  active  motion,  though  in  certain 
Crustacea,  for  instance,  they  lack  this  power.     The  ova  and 
spermatozoa  have  specialized  in  opposite  directions  in  this 
respect.     The  ova   of   the    Metazoa    are   specialized   as   the 
nutritive  cells  of  conjugation,  possessing  abundant  protoplasm 
and  usually  a  considerable  amount  of  yolk  for  the  nutrition 
of  the  young  embryo.     They  consequently   have    lost  their 
motility,  and  in  order  that  conjugation  may  be   made  prob- 
able the  spermatozoa  lack   all   unnecessary  material    which 
would  interfere  with  their  motility,  no  yolk  beiug  stored  up 
and   the    i)rot<)plasm    even    being    reduced  to    the    smallest 
amount  ^consistent   with    the    development   of   a   locomotor 
organ.     The  nuclei,  as  will  be  seen  later,   are  essential  ele- 
ments in  conjugation,  and  the  si)ern)atozoa  are  to  all  intents 
locomotor  nuclei,  the  ova  supplying  the  })rotoplasmic  nidus 
ne(!essary  for  the  growth  and  division  of  the  nucleus  formed 
l)_v  conjugation. 

In  their  typical  form  spermatozoa  are  composed  of  a 
globuhir  or  pyriform  head  consisting  of  a  nuchuis  surrounded 
by  a  small  amount  of  protophism,  and  a  long  lilamentous  (nil 
continuous  with  the  protoplasm  and  fre(|uently  provided  with 
u  delicate  fringe-like  niembrane  (Fig.  22,  A').  By  the  rai -' 
wliipj)ing  movements  of  the  tail  the  organism  is  prnpnUo,! 
tlirough  the  water,  or  other  tinid  in  which  it  may  iind  itself, 
ttiid  so  may  come  into  contact  with  an  ovum. 


§ 

c 

i 


48 


IN  VERTEBRA TE  MORPUOLOG  Y. 


The  trausforniation  of  the  germ-cells  present  iu  an  em 
bryo  into    spermatozoa   is   usually  a  somewhat  complicated 
process.     In  the    liouud-worm  Asians,    iu   which  it  retains 
somewhat    primitive  characters,  the  process    closely  resem- 
bles  what  takes  place  during  the  maturation  of  the  ovum» 


Fig.  23.— Diaohams  to  ii.i,u8tratk  the  .Matuhation  of  the  Spkum-cell. 

A  —  liivisioii  of  tlie  spermogoue. 
B  —  (livisiou  of  the  two  speruiocytes. 
C  =  the  four  spermatids. 
D,  E  —  conversion  of  a  spcrniaiid  into  a  spcrniiitozoon. 
F  —  fully  (levt'loped  speiinalozoon. 

The  embryonic  germ-cells  {spermatogones,  Fig.  22,  A)  undergo 
karyokiuetic  division,  the  number  of  chromosomes  being,  as 
in  the  ovum  in  the  division  which  results  iu  the  formation  of 
the  tirst  polar  globule,  twice  that  which  is  characteristic  for 
tl.>e  species.  Tliey  do  not  undergo  longitudinal  division,  and 
one  half  of  them  passes  into  one  of  the  daughter  cells  {spcr- 
iiKiforyft's)  and  tlie  other  half  into  the  otlier,  so  that  these  two 
cells  possess  the  numl)er  of  chromosomes  characteristic  for 
tlie  species.  A  division  of  these  daughter  cells  (Fig.  22,  />') 
immedial'ilv  takes  place  without  a  return  to  the  resting  stage, 
nnd  uuacc( uipanied  by  a  longitudinal  division  of  the  chromo- 
Hcunes,  so  that  four  cells  {sfM'i'nudids,  Fig.  22,  C)  are  formed, 
each  of  which  contains  only  half  the  ty]ucal  number  of  cliro- 
jjj(-ya(-)jj5P,ij  •j.jjd  p.jich  one  of  these  cells  becomes  a  s')erm;il'i- 
zoou.     This    process  is  comparable    step  by  step  with    the 


8UBKINQL0M  METAZOA.  4^ 

maturation  of  the  ovum  and  seems  to  indicate  tliat  the  polar 
globules  are  to  be  regarded  as  abortive  ova. 

The  conversion    of  the  spermatids    into   spermatozoa  ia 
simply  a  diflerentiatiou  of  structures    already   present      In 
the  air-breathing  Moliusca,  for  instance,  the  spermatids  consist 
of  a  mass  of  cytoplasm  containing  a  nucleus,  in  close  proxim- 
ity to  which  may  be  found  the  centrosome,  .vhile  an  irregular 
mass  of  filaments  represents  the  remains  of  the  spindle-tila- 
ments.     In  the  differentiation  which  follows  (Fig.  22,  1)  E 
iind    F)   the  nucleus  elongates  and   its  chromatin-filame'ntJ 
liise  to  form  a  homogeneous    mass ;  the  cytoplasm  likewise 
elongates,  and  m  it  appears  an  axial  filament  which  later  will 
form  the  tail-tilament.     The  origin  of  this  filament  is  doubt- 
ful, some  authors  maintaining  that  it  is  a  difterentiation  of 
the  cytoplasm,  while  others  believe  it  to  be  a  prolongation  of 
the  nuclear  substance ;  but,  however  that  may  be,  the  spiral 
Irmge    which  surrounds  the   axial  filament  is  certainly   the 
remaiiis  of  the  cytoplasm  of  the  spermatid.     The  remains  of 
the  spindle-fiiaments  disappear,  while  the  centrosome  prob- 
ably persists  as  a  structure  lying  behind  the  head  and  termed 
the  "Mittelstiick." 

Ill  some  cases  as  the  insect  P,,nh.eoyl,  and  the  crnsfacean  mrptomm, 
I..' duubhnjj  of  the  chromosomes  previous  to  division  into  spermatocytes 
.I0..S  not  take  place.     In  />,n-/.>c../,vtwenty-four  ^^.::::^T^. 
.ally  present  and  twelve  of  tln-se  pass  into  each  of  the  spermatocvtes    u.d 
.1.  the  d.v.s.on  of  these  to  forn.  the  spern.atids  each  of  tl.e  twelve  eh'r'omo 
.Jom^d.VKles  so  that  each  spermatid  possesses  half  the  typical  nnn.her. 
.  JhupUunn.  the  sann,>  resnlt  is  brought  about  somewhat  differentiv 
he  sperniatoKoncs  possess  eij,d>t  ehro.nosomes  which  assume  a  dund.bni 
sLape  anddnule  transversely,  so  that  each  spermatocyte  has  tl.e  t   pi  a 
■unnber    of    chron.oson.es  ;    ,he    spern.atocytes    divi<i;   wthou      p         g 
-lirouKh  arestm.^  stage,  and  each  spern.atid  thus  contains  four  c  u'omo 
M)incs,  I.e.  hall  the  typical  number.  ^"lomo 

FertilizaiHrn  of  the  Ovnm.~?^o  soon  as  the  formation  of  the 
l'«;hirgh,buh>slms  been  completed,  the  nucleus  of  the  ovum 
..ugntteH  towards  the  centre  of  tlie  protoplasm  ami  is  th„ 
tnnule^nuden.  (Fig.  23,  ./>,)  of  conjugation.  The  penetia- 
t">n  o  the  spermatozoon  may  occur  at  any  p,)rtion  of  th.«  sur- 
I'-e  of  the  ovum  and  may  take  place  before,  during  (Fi«  21 
A.  sp\  or  after  the  formation  of  the  polar  gh.bules,  a  single 


U&t'liii 


m 


W VERTEBRA TE  MORPHOLOG  Y. 


spermatozoon,  as  a  rule,  in  healthy  ova,  penetrating  and  tak- 
ing part  in  the  conjugation,  though  apparently  in  some  cases 
polyspermy,  or  the  penetration  of  several  spermatozoa,  may 
occur.  The  head  of  the  spermatozoon  comes  into  contact 
with  the  protoplasm  of  the  ovum,  which  in  some  cases  rises 
up  to  meet  it,  and  is  rapidly  engulfed.     The  tail  likewise  of 


C D 

Fm.  23.— Diagrams  to  Illustkate  the  Piiknomena  of  Fertilizatiox. 

(From  flf?ures  by  E.  B.  Wilson.) 

A,  the  approximation  of  the  male  and  female  pronuclei. 

B,  division  of  tiie  arclioplasm. 

V,  separation  of  the  arclioplasm  spheres. 

D,  fusion  of  the  pronuclei,  and  formation  of  the  segmentation  spindle. 

//)  =  female  pronucleus.  a  =  arclioplasm. 

mp  =  male  pronucleus.  sn  =  segmentation  nucleus. 

the  spermatozoon  is  taken  into  tlie  ovum  and  seems  to  ho 
completely  absorbed,  the  head  alone  being  visible  in  later 
stages  ;  it  constitutes  the  viale  pronuclem  (Fig.  28,  mp),  and 
moves  towards  the  centre  of  the  egg  until  it  comes  into'con- 
tactwith  the  female  pronucleus,  fusing  with  it  to  form  the  sey- 
menfation  nudeus.  A  spindle  now  makes  its  appearance,  and  the 
Bogmentatiou  nucleus  passes  through  the  various  karyokinetic 
stages,  forming  an  equatorial  plate  with  the  typical  number 


SUBKINGDOM   METAZOA. 


51 


of  chromosomes,  which  divide  lougitudiually  in  the  usual 
in.'umer,  cue  half  of  them  passing  towards  each  of  the  archo- 
plasin  spheres.  The  ovum  then  divides  into  two  cells,  the 
nuclei  of  which  each  possess  chromatin  elements  from  both 
the  male  and  the  female  pronuclei. 

It  will  be  seen  from  this  that  the  conjugation  or  fertiliza- 
tion process  consists  of  the  union  of  two  distinct  nuclei,  whose 
complete  fusion  however  does  not  necessarily  occur  until 
after  the  first  division  or  segmentation  of  the  ovum. 

The  archoplasm  of  the  segmentation  nucleus  is  derived 
as  a  rule,  from  the  sperm-cell  alone  (Fig.  24),  that  which  ex- 
isted in  the  ovum  during  its  maturation  disappearing  before 
fortdization  takes  place.  It  has  been  claimed,  however,  that 
ill  some  cases  the  ovum  archoplasm  persists,  and  unites  with 
tiiat  from  the  sperm  when  the  pronuclei  unite,  and  that 
more  rarely  the  ovum  archoplasm  alone  persists.  These  ob- 
servations, however,  need  confirmation. 

Furthermore,  in  some  cases  at  least,  it  is  possible  to  dis- 
tinguish the  nuclear  elements  derived  from  the  male  and 
female  pronuclei  respectively  in  stages  later  than  the  first 
segmentation,  owing  to  a  slightly  different  behavior  to  certain 
staining  reagents  which  chara,cterizes  them.  The  pronuclei 
undergo  a  morphological  fusion  during  the  first  cleavage  of 
the  ovum,  but  a  physiological  difierentiation  persists. 

Segmentation  and  EarJy  Ih'relopinent  of  the  Ovum.— The 
development  of  the  ovum  into  the  embryo  consists  in  its  divi- 
sion  into  a  number  of  cells,  which  gradually  undergo  a  pliy- 
sioiogical  and  morphological  difierentiation  resulting  in  the 
formation  of  tissues,  organs,  etc.  These  divisions  constitute 
the  segmentation  of  the  ovum. 

The  first  division  has  already  been  described ;  it  bears  a 
definite  relation  to  the  formation  of  the  polar  globules,  the 
l)lane  of  the  division  ])assing  through  the  p.)int  at  which  they 
Mere  separated  from  the  ovum.  Considering  this  point  to 
represent  one  pole  of  the  ovum,  the  first  division  is  meridio- 
iial,  and  the  second  divisi(ui  likewise,  though  its  plane  is  at 
right  angles  to  that  of  tlie  first  division  (Fig.  2^  A).  The 
third  division  is,  tm  tho  otlier  iiand,  equatorial,  its  plane  cutting 
the  planes  of  [)revious  divisions  at  right  angles  (Fig.  24,  Hl 


i 

I 

i 

i 


^mammmmmmm 


m 


INVERTEBRATE  MORPHOLOGY. 


Eight  segineutatiou-cella  are  tlius  furiued  which  remaiu  in 
^outaet  with  each  other  aud  enclose  a  small  cavity,  the  seg- 
meiitatiou-cavity  or  blastocoel.  The  further  divisiou  of  the 
cells  (Fig.  24,  C)  results  in  the  formation  of  an  oval  or  spheri- 
cal organism  (Fig.  24,  JJ)  which  may  be  compared  to  Volvox, 
consisting  of  a  single  layer  of  cells  enclosing  a  more  or  less 
voluminous  blastocuel.  This  embryonic  stage  is  known  as 
the  hlostula.  In  its  simplest  form  it  shows  no  special  differ- 
entiation into  tissues,  its  cells  being  uniformly  ciliated,  and 


Fig.  34  —Diagrams  illusthating  the  Segmentation  op  the  Ovum. 

A,  four-celled  stage. 

B,  ei,i;lit-celleil  stujje  of  a  telolecithal  ovum. 
f,  sixteeu-ccUed  stage. 

1),  blualula. 
Tlio  arrows  ludicate  the  mode  of  divisiou. 

the  organism  free-swimming,  moving  through  the  water  with 
a  rotatory  movement  about  a  dehuite  axis,  one  and  the  same 
end  of  which  is  always  anterior.  In  many  blastulas,  however, 
especially  in  those  which  for  one  reason  or  another  are  not 
free-swimming,  an  early  differentiation  of  the  cells  takes  place, 
especially  at  the  extremity  which  is  posterior  in  the  free- 
swimming  forms  or  which  corresponds  to  that  pole  in  the 
non-motile  embryos.     These  posterior  cells  are  usually  sonie- 

xirlinf  Ini'dfor  flimi   flirisft  n.^.  flip  nufftvinr  r)ole-   n.ud   if  lYinnli    foo    - 

jolk  is  present  in  the  embryo  it  is  especially  concentrated  lu 


8UBKINOD0M  METAZOA.  03 

these  cells,  which  in  the  later  developmeut  will  assume  the 
vegetative  fuuctious  of  the  orgauism. 

In  many  ova  the  processes  just  described  are  modified  to  a  greater  or 
1..SS  extent,  but  from  tlie  frequency  of  tlieir  occurrence  they  must  be  re 
garded  as  fundamental  and  the  modifications  as  secondary 

Ova  which  contain  but  little  yolk  usually  follow  more  or  less  closelv 
the  typical  processes,  but  wher^.  the  yolk  is  abundant,  being  an  inert  sub 
stimce,  It  acts  as  a  drag  upon  the  protoplasmic  activity  and  produces  modi 
lioation  of  the  segmentation-processes.     Two  methods  of  arrangement  of 
tl.e  yolk  may  be  recognized  :  (a)  it  may  be  aggregated  more  or^less  com- 
pletely at,  one  pole  of  the  ovum,  such  ova  being  termed  telolecithal  or  (h) 
It  may  be  distributed  in  the  meshes  of  a  protoplasmic  network  a  small 
(luantity  of  yolkless  protoplasm  being  concentrated  around  the  nucleus  of 
tlie  ovum,  while  another  portion  of  it  forms  a  thin  peripheral  layer  sur 
rounding  the  yolk,  this  arrangement  being  termed  centrolecithal 

In  telolecithal  ova  the  third  segmentation-division  results  in  the  forma 
tion  of  tour  cells  containing  very  little  yolk  at  one  pole  of  tlie  ovum   while 
nearly  all  the  yolk  is  concentrated  in  the  four  cells  at  the  other  pole  (Fi- 
24,  B).    This  arrangement,  which  occurs  in  many  Mollusca,  constitutes 
what  IS  termed  a  total  irregular  segmentation,  in  which,  owing  to  tlie  lar<re 
size  of  the  yolk-containing  vegetative  cells,  the  blastocoel  is  usually  com- 
paratively small.    In  the  Squids  the  amount  of  yolk  present  at  the  vegetative 
pole  is  very  great  and  the  protoplasm  of  the  ovum  collects  upon  its  surface 
there  undergoing  division  and  producing  a  plate  of  cells,  the  blastoderm' 
which  by  further  division  gradually  extends  and  finally  encloses  the  inert 
yolk.    This  partial  segmentation  is  the  result  of  the  presence  of  a  very 
large  quantity  of  yolk  and  its  telolecithal  arrangement,  and  necessarilv 
obscures  greatly  the  blastula  stage. 

In  centrolecithal  ova  which  occur  in  Crustacea  and  Insects,  the  division 
of  the  nucleus  is  accompanied  by  a  division  of  the  central  yolkless  proto- 
plasm only,  the  yolk-containing  reticulum  and  the  peripheral  layer  not  tak- 
ing part  in  the  process.  As  the  divisions  continue  the  nuclei  gradually 
approach  the  surface  and  finally  come  to  lie  in  the  peripheral  protoplasm 
winch  then  takes  part  in  the  division,  a  greater  or  less  portion  of  the  inert 
undivided  yolk  occupying  the  blastocoel  of  the  resulting  blastula  Many 
intermediate  gradations  occur  between  such  a  typical  centrolecithal  and  a 
otal  regular  segmentation,  from  which  both  the  centrolecithal  and  telo- 
lecithal methods  are  to  be  derived. 

The  blastula  is  a  single  layer  of  cells  surrouudiug  a  large 
blastocoel  in  typical  cases,  and  is  a  stage  quickly  passed  over 
in  the  Metazoa.  It  is  succeeded  by  a  stage  in  which  the  em- 
bryo consists  of  a  doublp-wallGd  sac  open  at  utie  end,  th 


trula  (Fig.  25).     This  is  most  fr 


ne 


J/((6'- 


equeutly  produced  from  the 


■SeiltKiiiimilimamamit.v 


rA 


INVERTEBRATE  MORPHOLOGY. 


14' 


Fig.  3o.— Diagram  of  a  Gastkula. 


biiistula  by  the  piishiug  in  or  invagr.iation  of  the  cells  of  011& 
pole  (the  posterior  in  free-swimming  blastulas)  into  the  bias- 
tocoel,  which  thus  becomes  more  or  less  perfectly  obliternteJ. 

The  cavity  lined  by  the  iuvagi- 
nated  ceils  is  the  primitive  di- 
gestive tract  or  archenteron,  its 
opening  to  the  exterior  being 
the  gastrula  mouth  or  blastopore. 
The  gastrula  is  a  two-layered 
organism  or  is  diplohlastic,  and 
the  cell-layers  of  which  it  is 
composed  are  the  primitive  germ- 
layers.  The  outer  layer  in  the 
higher  Metazoa  gives  rise  to  the 
integument,  nervous  system,  and 
sense-organs  of  the  adult  and 
is  known  as  the  ectoderm,  while 
the  inner  one,  from  which  the  digestive  tract  and  its  glands, 
such  as  th(i  liver,  will  develop,  is  termed  the  endoderm. 

Just  as  the  presence  of  yolk  in  the  ovum  may  modify  the 
segmentation,  so  too  it  may  produce  decided  modifications  in 
the  formation  of  the  gastrula.  The  method  just  described, 
which  occurs  in  embryos  containing  little  food-yolk,  is  distin- 
guished as  embolic  from  the  epibolic  motl:od  occurring  in  telo 
lecithal  ova  which  undergo  a  markedly  irregular  segmentation. 
In  such  ova,  as  has  been  stated,  one  pole  is  occupied  by  inert 
yolk-loden  spherules,  while  at  the  other  are  almost  yolkless 
active  cells.  These  latter  divide  rapidly  and  extend  as  a  cup 
over  the  yolk-laden  cells  and  finally  completely  enclose  them. 
The  result  is  practically  the  same  as  in  the  embolic  method, 
the  yolk-laden  endoderm  cells  being  enclosed  within  the  yolk- 
less  ectoderm. 

Among  the  lower  Metazoa  especially,  another  method  oc- 
curs by  which  the  diploblastic  embryo  is  formed.  Instead  of 
certain  cells  invaginating,  each  cell  of  the  blastula  divides  iu 
a  plane  parallel  to  the  surface  of  the  organism,  one  of  the  two 
cells  thus  produced  becoming  ectoderm,  while  the  otiier  is  a 
portion  of  the  endoderm.  A  diploblastic  closed  sac  thus  re- 
sults, the  blastopore  appearing  later  and  placing  the  archeii- 


tiUBKlJVGDOM  METAZOA.  /)5 

terou,  which  iu  this  ca«e  is  identical  with  the  bhistocoel  iu 
commuuication  with  the  exterior.  This  process  is  known  as 
lii'ldiidnatiijn  {¥\^.  20,  A). 

A  third  method  also  exists,  occurring  liko  delamination  in 
its  most  typical  form  ixmoix^  the  lower  Metazoa.  This  is  the 
i,nmi<jration  method  (Fig.  20,  /i),  certain  cells  of  the  })lastula 
leaving  their  position  at  tlio  surface  and  passing  into  the 
l.lastociL'l.  Here  they  undergo  division,  and,  by  the  addition 
of  other  cells  by  immigration,  the  blascoccel  gradually  be- 
comes filled  iip  and  a  solid  organism,  consisting  of  an  exter- 
nal layer  of  cells  surrounding  a  central  more  or  less  solid 


Fig.  26.-DIAGUAM  Illustuatino  the  Formation  op  the  Dipi.oblxstic 
bTAGE  (A)  BY  Delamination,  (B)  by  Immiguation. 

I  niass,  results.     This  is  known  as  the  parenchymella  or  sterrida 
Luter  a  cavity  appears  in  the  centre  of  the  solid  mass,  whose 
cells  gradually  are  pushed  towards  tne  periphery,  where  they 
lorm  eventually  a  single  layer,  the  endoderm.     Finally  a  blas- 

|to})ore  18  formed  and  the  embryo  becomes  a  gastrula. 

It  does  not  seem  easy  to   bring  the  delnmination   and  invagination 
•"...tl.odsof  gastrulation  into  direct  relation  with  each  other,  or  to  derive 
une  trom  the  other,  but  it  is  probable  tliat  both  must  be  referred  back  to 
tlH'  niunigration  method.     In  typical  cases  of  immigration  the  cells  which 
mi^nito  are  situated  irregularly  at  any  part  of  the  blastula,  but  frequently 
-pec..a  ly  in  free-swimming  blastulas,  the  ...igrating  cells  are  all  located  aJ 
postenor  extreu.ity,     If  in  such  cases  of  polar  immigration  the  migrat- 
.ee  Is  were  to  pass  into  the  blastoca^l  en  mcme  instead  of  indivichmllv 
I    u«  nation  would  result.     On  the  other  hand,  if  a  considerable  amount, 
of  u.lk  were  present  m  all  the  cells  of  a  blastula.  it  might  hannn.,  thv   itl 
-aa  ot  migrating,  the  cell  might  undergo  division,  cutting  off  the'  volk- 
[-"■•uuing  protoplasm  from  the  yolkless,  delamination  thn.  taking  pir'.. 


66 


IN  VERTEBRA  TE  MORPIIOLOO  Y. 


Tlie  fact  that  in  some  cases  both  imiuigratiuu  and  delamination  may  occur 
simultaneously,  leading  to  the  formation  of  a  sterrula,  bears  out  the  idea 
that  the  latter  process  has  arisen  from  the  former. 

Furthermore,  it  may  be  pointed  out  tluit  the  occurrence  of  i-^amigratioii 
in  such  colonial  Flagellates  as  Volmx  indicates,  the  primitive  character  of 
immigration  in  the  Metazoan  blastulas,  as  well  as  the  manner  in  whioli 
diploblastic  organisms  have  arisen  from  the  more  primitive  single-layered 
organisms. 

It  is  only  in  the  lowest  Metazoa,  however,  that  the  adult 
organism  is  diploblastic.     In  all  others  a  triploblastic  (Fig. 


am 


sm 


spm 


VTTV 


Fig.  27.- 


-DlAGKAMMATIC    TRANSVKnSE    SECTION     OF    AN     EaKTIIWORM    TO 
SHOW    THE    TUIPLOllLASTIC   CONDITION. 


bm  =  basement  membrane. 

V  =  coelom. 
dm  —  dorsal  mesentery. 

ec  =  ectoderm. 


en  —  endoderm. 
sm  —  somatic  mesoderm. 
spm  —  splanchnic  mesoderm. 
vm  =  ventral  mesentery. 


27)  condition  supervenes  during  embryonic  life,  by  the  devel- 
opment of  a  third  layer,  primitively  separated  from  the  endo- 
derm, and  occupying  the  space  Avhich  may  remain  betweeu 
the  two  primitive  layers.  This  is  the  secondary  germ-layer 
or  mesoderm.  From  it  there  arise  the  muscular,  excretory, 
circulatory,  and  reproductive  systems  in  the  triploblastic  ani- 
mals, the  first  and  last  of  these  being  derived  in  diploblastic 
forms  from  either  one  or  both  of  the  primary  layers,  while 
the  excretory  and  circulatory  systems  are  not  differentiated. 

The  manner  of  formation  of  the  mesoderm  in  the  embryo  I 
varies  greatly.     In  some  cases  it  arises  as  bilateral  pouch-like 
outgrowths  of  the  archenteron,  which  later  form  closed  sacks 
completely  surrounding  the  digestive  tract,  the  sack  of  either i 


Qeniiic  pouches.     A 


SUBKINODOM  METAZOA. 


57 

«ide  coming  into  contact  above  ami  below,  the  united  walls 
brining  the  dorsal  and  ventral  mesenteries  which  snsDemTt 
intestine  (Fig.  27.  am  and  bm).     That  wall  of  e-i  1.  !    l  ? 

surrounds  the  digestive  tracti  ieJjil:l^^^:^:^ 
lie  mesoderm  (Fig.  27,  sp>n),  while   that  l/ng  imn  eZ Lv 
below  the  ectoderm  is  the  somatic  layer  (m)  and    iTl  f     ^ 
cavitj  is  the  ccelom  (C)  or  body-cavitv      T,  enclosed 

protoplasm  destined  to  give  r^e  to  tl  1  n..  7        '  ""'  '^" 
iato  a  small  number  of  ce  Is   or  sonw  '"•    ''^''^^^''^ 

i  ^^...P      tLo  1  ''^  ^^  considered  the  blastula 

stage.     Ihese  cells,  known  as  mesoMasts,  give  rise  by  rene.f. 
division  in  one  direction   nn.l  i.„  +i  i  ^  lejaeated 

'  the  dauditer  o.ul       7         }  ^  ^'^  subsequent  division  of 

iu,)j,  and  later  crrowino-  rlm-u-illTr  ..^        i  ,  ^  ^" 

tive  tropf      Tl.  ,    "^  ^'^'^'^^^y  «o  as  to  enclose  the  di«es. 

£-::,.  ;t,r '2 ':;::  ,xxtA:i  -  j: 

same  appearance  as  in  the  former  case  Presents   the 

Jbeing  minute  scattered  cavities  in  n  mnL  ^f  ^ 

'lerm,  it  would  seem  that  Zim   Z  ^      "''""  ''^'^  ""^""  "^  *''«  '»««o- 

'f  ti>o  nature  of  a  scliiJl      'f.1  f     ^  S";'"'"  '""*  '^  ^""^"'"'"^^  "'^'^ 

-norodifferentiatedfrr^eend  d    ™^^^  '^^""^  '"-'^  -'^ 

^s  a  separate  germ-layer  .t  an  e-^J  ?  P'-oper  and  either  tende<l  to  appear 

he  n>esoblasts  or  wa   del-  v'd  i n   N  T'"^        ^'^^'^^opment  in  the  fonn  of 

>f  ••"■  PHmitivo  di..e3  i  0  hnct  7.       ^^^^'l^P'"'^"^  ""^il  after  the  fofmatio. 

--'ouches.  ird::;r:oth- rth^t^^^^^^^^ 


111) 


I  I 


58 


INVERTEBRATE  MORPHOLOGY. 


derivative  of  the  endoderm,  and  the  endoderm  of  the  diploblastic  organ- 
isms is  equivalent  to  the  endoderm  plus  mesoderm  of  tiie  triploblasiic 
forms.  The  apparent  derivation  of  the  mesoderm  from  the  ectoderm  in 
.some  of  the  latter  (e.g.  Annelida)  is  to  be  regarded  ao  resulting  from  tins 
l)recocious  segregation  of  the  mesoderm  at  an  early  period  of  development 
and  is  not  to  be  regarded  as  indicating  its  original  derivation. 

Ko7i-sexual  licproduciion  in  the  Metazoa. — Reproduction  hx 
division  and  by  budding,  though  playing  by  no  means  so  im- 
portant a  part  as  in  tlie  Protozoa,  is  neverthe- 
less  of   frequent   occurrence  in  the  Metazoa, 
\m        especially  in  certain  groups.     In  certain  Tiir- 
bellariau  worms  (3Iicro.sto)na)  division  is  the 
'"        usual  mode  of  reproduction,  replacing  almost 
,,         completely  the  sexual  method,  and,  the  indi- 
viduals so  produced  remaining  in  connection 
fin         with    one    another,    longitudinal    chains    aie 
]>roduced,  ct)nsistiug  of  individuals  in  various 
m»       degrees   of  separation    (Fig.    28).     In    certain 
Annelids    also   <Naidid«>)    division    frequently 
|ni"<        takes  place,  occasional!}' each  metamere  beinif 
capable  of  developing  into  a  new  animal,  as  in 
Ctenodrilths. 
>'  Budding,   however,    is  a  rather  more   fre- 

(juent  method  and  is  characteristic  of  certain 
groups,  such  as  the  Hydroids,  Anthozoa,  and 
Fid.    28.  — -  D I  A-  Jjfyoijoa.     In   some  cases,  as   in    Hydra    and 
ouAM     smnviNo  ^^^[^^^^    medusie,   the   buds   se])arate  "from    the 

NON-8KXUAI,    ItK-  i      i         n  •      i  i 

ruoDicTKiN    OK  P"^'"^"''   •'^''*'    ^6ad    an   independent  existence; 
A  Tchuki.i.ahian  but  frcnpuMitly  the  se])aration  is  not  com])leto, 
WouM    MiiTOMto-  resulting    in    the    foiinution    of   colonies    tlie 
'""      "'^'*'''     """  individual    components    of   which  are   in  or- 
ganic  connection   with    each   other.     In    sucli 
colonies    a    physiological    division  of   labor  aniong   the  con- 
stituent   individuals    may    talu^    ])lace,    as    in    the    Hydroid 
//ydrnefiiiiii  (se<!  p.  87)  where  some  of  the  individuals  devote 
themselves    to    the    nutrition    of    the    colony,   others   to   its 
re])roduction,    and    otluTs    again    to  tiie    protection  of   tlnii' 
weaker  companions.      The  assemblages   produced    by    buil- 
ding   may    assume  very   complicated    shapes,    though    ocou- 


SUDKINGDOM  METAZOA.  59 

sionally  linear  eolouies  are  formed  wliieh  are  with  difficnltv 
to  bechstiuouLsiiea  from  those  formed  by  division.  Indeed 
a  dehnite  distinction  between  budding  and  division  is  not 
possible,  though  where  an  alternation  of  older  and  younger 
individuals  occurs  in  a  linear  colony  division  is  indicated, 
wlide  in  one  produced  by  budding  there  is  a  regular  succes^ 
sion  of  gradually  older  individuals  from  before  backwards 

Closely  related  to  budding  is  the  power  of  regeneration 
of  parts      Ihe    higlier   Crustacea  possess   an  extraordinary 
IKnver  of  i-egenerating  lost  limbs,  and  provision  is  present  in 
crabs  and  the  lobster  for  the  self-amputation  of  a  limb  when 
such  a  mutilation  seems  to  be  demanded  by  the  exigencies 
o    the  situation.     In  the  lower  forms,  lu    .ever,  the  extent  to 
Avhicli  such  regeneration  may  be  carried  is  much  greater  ex- 
ten,  ing  even  to  the  reproduction  of  the  whole  by  a  compara- 
tively snmll  part.     A  Starfish  is  not  only  able  to  regenerate 
an  arni  which  has  been  accidentally  lost,  but  from  an  arm  an.l 
a  portion  of  the  disk  all  the  missing  parts  mav  be  developed  • 
Uxiui  Hydra  or  a  Sponge  may  l,e  divided  into"a  large  numl)er 
ot  pieces  each  of  which  is  capable  of  deveh.pinginto  an  entire 
<J"in.aI      Such  phenomena,  as  well  as  budding  and  division 
dq.ond  either  upon   a  low  degree  of  difierentiation  of   the' 
issues,  as  in  such  a  form  as  a  Sp.mge  or  in  lly^/ra,  or  else  to 
the  persistence  of  a  certain  amount  of  tissue  in  an  embrvonic 
Yl  nndilierent.ated    condition.     In  a  Brvozoan  bud.  for  in- 
stance,  as  its  tissues  gradually  dimn-entiate   into  the  adult 
co-..htion,  a  niunber  of  cells  lag  ]>ehind  and  do  not  take  part 
1"  i\y^  ditterentiation,  and  later  give  rise  to  a  new  bu.l ;  and 
sundarly  ,n  the  Annelid  worms  the  tissues  of  a  regeneratin.^ 
I'Mi-l  Hhow  an  appearance  and  nn.de  of  ditierentiati,.n  similar 
ywhat    hey    present  in    the    development  from   the    ovum. 
...iversely  the  greater  the  degree  of  dim-rentiation   an<l   in- 
t.'Knit,.on   of    the    tissues   and  organs  of   an  anin.al   the  less 
llld !lh/'''''''  "^  i-eKenerating  lost  parts  or  of  repro.Jucing  by 

L  I,;,;,'  ^'""'r'  '■•''^'  "^'^  ^''^  incapable  of  developing  into  the 
It  torn,  unless  fertilised  by  a  Hpermatozoon.     In  a  number 


11^  however,  a  development  of  nufertili/,.d 


L'oii.stitufmg   a    mode    (.(' 


o\  M     ni'ciir'J 


i 

r 
I 


I'l 


production    kn 


own    as    futrlli 


'H'tlO- 


60 


INVERTEBRATE  MORPIIOLOG T. 


geiiesis.     Examples  of  this  phenomenon  are  to  be  met  with  in 
Insects,  a   familiar   one   being  the   common   Hive   Bee,  the 
queens   of   which    species    deposit    large    numbers   of   eggs, 
those  last  deposited,  which  give  rise  to  drones,  being  unfer- 
tilized and  developing  parthenogeneticall}'.     In  certain  flies 
[Cecidomyki)   this    parthenogenetic   development   of   the  ova 
may  occur  while  the  insect  is  still  in  the  larval  or  maggot 
stage,  a  phenomenon  which  is  known  as  pcedoc^nesis  (Fig.  29). 
Alternation  of  Generations. — The  majority  oi  forms  which 
possess   the   power  of    non-sexual  reproduction   also    repro- 
duce by  the  sexual  method,  no  definite  relation 
existing,  however,  between  the  two  processes. 
In  some  cases,  however,  a  definite  relation  is 
established,  the    one   method  succeeding  the 
other  with  rhythmic  regularity,  the  individuals 
also  which  reproduce  sexually  differing  materi- 
all}'  in  form  and  organization  from  those  Avhicli 
gave   rise  to  them   by  a  non-sexual  method ; 
such  a  condition   of  aft'airs  is    termed  Alter- 
nation  of    Generations,    a   generation    of    in- 
dividuals  reproducing  only   by  a  non-sexual 
method  alternating  Avith  a  second  generation 
reproducing   exclusively  or   almost  so  in  the 
sexual    manner.      Typical  examples    of    this 
process    are    afforded    by  the    Discomedusa', 
in    many   of   which   the  individual   produced 
by  the  develoinueut  of  the  ovum   is    a  fixed, 
cylindrical  organism  of  simple  structure,  knouu 
icido-^^  ^  P^^llPf  possessing  the  i)ower  of  non  sexual 
w//'"  liAuvA  (after  reproduction   (see   Fig.  55).      By  a   series  of 
!'A(.K.NKTK.MKu  fro...  truusverse  divisions  it    gives  rise  to  a  linear 

nATHrllKK).  ...  .  . 

colony  of  individuals  which  in  the  course  of 
dovelopraent  assume  a  form  very  different  from  that  of  the 
parent  polvj),  becoming  more  complicated  in  structure,  more 
highly  organized,  and  free-swimming.  These  organisms, 
known  as  Mcdmrp,  are  the  sexual  generation,  producing  sjxm- 
matozoa  and  ova,  the  latter  after  fertilization  developing'  a  | 
non-sexual  generation,  a  polyj),  with  which  the  cycle  begins  I 
again. 


Fki.   29.  —  P^:do 

UKNKTIC 


SUBKINGDOM  METAZOA. 


61 


Selieinatically  such  an  arrangement  may  be  represented  thus,  A  repre- 
senting the  non-sexual  and  B  the  sexual  generation  : 

/B— A,  etc. 
a//B—A,  etc. 
"^XxB-A,  etc. 

\B— A,  etc. 

Among  the  Hydromedusa?,  in  which  group  alternation  of  generations 
likewise  occurs,  the  process  is  usually  complicated  by  a  number  of  non- 
sexual generations  succeeding  one  another  before  the  intervention  of  the 
Medusa,  thus  : 

/A" 

^/'^'\A'   :^  B  =  A.  etc. 

'^\,yA"  =  li  =  A,etc. 
"^  \A' 

And  in  some  cases  the  succession  is  still  further  complicated  by  non-sexual 
reproduction  on  the  part  of  tlie  medusa,  thus  : 


,yA' 


A,  etc. 


a{  \'^  =  A,  etc. 

^^'^^l"~\\^'  =  A,etc. 

A,  etc. 

But  such  complications  do  not  interfere  with  the  general  alternation 
which  invariably  occurs  in  such  forms  before  the  completion  of  the  renro- 
(iuetive  cycle.  ' 

Such  a  phenomenon  as  this  where  a  true  uou-sexuul  .^eu- 
Hi-atiou  alternates  witli  a  sexual  one   presenting  a  diflerent 
structure  is  usually  distinguished  as  metagenesis  from  another 
l-nn   of  alternation  of  generations    known  as  heterogony,  in 
which   the   first   generation  re])roduces  p>irthenogenetieallj, 
giving  rise  to  a  second  generation  ditlering  in  form  from  the' 
Hrst  and  reproducing  by  the  sexual  method.     'J'vpical  exam- 
)'I<"s  of  this  process  are  to  be  found  among  the  Trematode 
worms  ((,.v.),  where  the  sexual  worm  gives  rise  to  a  sporocyst 
n.  the  interior  of  which  ova,  developing  parthenoger.'ticallv 
give  rise  to  a  larva  which  later  on  transforms  to  the  adult 
worm.     In  a  less  perfect   form   heterogony  occurs  in  many 
lower   Crustacea  {Daphma),  which    throughout    the    warmer 
portion  of  the  year  produce  "summer  eu'gs  "  which  dfivelop 
IMrthenogeneticaily,  male  animals  a])pearing  onlv  f..r  ,■.  slinrf 


l»i  rind  in  the  autumn, 


as  a  I 


ule,  when  the  lemules  produce 


62 


IN  VEHTEBliA  TE  MORPllOLOG  Y. 


"  winter  oggs  "  which  develop  after  fertilization.  Here  no 
difference  of  form  exists  between  the  two  generations,  but 
such  cases,  as  well  as  those  in  which  two  sexual  generations 
unlike  in  form  and  habitat  alternate  Avith  each  other,  are 
usually  associated  with  the  more  typical  examples  as  in- 
stances of  heterogony. 


TltWUOPLA 


LITERATURE. 

0,  Hertwig.     Beitrage  zur  Kenntniss  der  IHldung,  Befi  uchtung  tind  Theilung 

dfs  thierisrhen  Eics.     Morpholog.  Jabrbucb,  r.,  iii.  and  iv.  1875-78. 
E.  van  Beneden  and  A.  Neyt.     Nouvellcs  rccherches  sur  la  tWondntion  et  la 

dmsion  mitodque  rhez  I'Asmride  megalocephale.      Bulletin  de  la  Societ(' 

royale  Belgiqne,  xiv.  1887. 
Th.  Boveri.     ZeUenstudien.     Jenaisclie  Zeitsclirift,  xxii.  1888  and  xxiv.  1890. 
E.  B.  Wilson.     Archopltism,  Centrosome,  <ind  Chroviatiti  in  the  Sea-urchin  Eyg. 

Jomiijil  of  3Iorpli<)l()gy.  xr.  189."). 

0.  Hertwig.      Vcrgldch    der  Ei-  und   Samenbildung  bei  Nematoden.    Archiv 

fUr  mikrosk.  Anntoniie,  xxxvr.  1890. 

1.  M.  Balfour.     A  Tmitixe  on  Coiuparaticc  Emhryology.     London,  1880. 
E.  Metschnikoflf.     Embvyologischc  Sdidicn  on  Mfdnsen.     Vienna,  1886. 

E.  Haeckel.     Lie   Gastnda  und  die  Eifurchung  der  Thieve.    Jenaisclie  Zeit- 
sclir.,  IX.  1873. 


TllWUOPLAX.  THE  DIVYEMW^  AND  OHTHONEVTW^. 


63 


CHAPTER  IV. 

fRiOHOPLAX,  THE  DICYEMID^  AND  ORTHONECTID^. 

Before  passiug  on  to  a  description  of  the  first  type  of 
Metazoa  it  will  be  necessary  to  consider  a  few  forn^s  which 
can  hardly  be  assigned  to  it  and  yet  present  to,,  great  a  dif- 
ferentiation  of  their  component  cells  to  warrant  their  reference 
to  the  Protozoa.  A  third  subkingdom,  the  Me.sozoa,  has  been 
proposed  for  them,  but  until  more  is  known  of  the  relations^ 
of  some  of  them  at  least  to  other  forms  the  establishment  of 
suclj  a  subkingdom  seems  inadvisable. 

Trichoplax  ad/wrens. 


F.O.  30.-^.  SruKACK.  VrP.w  anp  R  Tuanhvkhse  Section  thuoioh  Tncho 

PiflJ"  (after  Si'hoi.zk). 

b  =  botiyoi.ial  structure.  ,.  =  ,,.f,actlve  bodies. 

In.  the  marine  aquaria  at  Oraiz,  Vienna,  and  Berlin  there 
J'Hs  been  found  a  small  organism  (Fig.  30,  A)  measuriijg  from 


IH^ 


64 


IN  VERTEBRA  TE  MORPHOLOG  Y. 


1.5  to  4  ram.,  but  capable  of  great  alteration  of  form.  It  is 
flatteued,  and  creeps  about  upon  the  walls  of  the  aquaria  iu 
an  amoeboid  manner.  It  consists,  however,  of  numerous  cells 
(Fig.  30,  B),  the  upper  surface  being  covered  by  a  flatteued 
ciliated  epithelium,  and  the  lower  formed  by  a  layer  of 
columnar  cells  also  ciliated,  while  the  space  between  the  two 
surfaces  is  occupied  by  a  network  of  branching  cells,  the 
branches  appearing  to  unite  with  those  of  adjacent  cells  and 
with  prolongations  from  both  the  upper  and  the  lower  epithe- 
lium. The  arrangement  suggests  the  three  germ-layers  ecto- 
derm, eudoderm,  and  mesoderm,  but  until  more  is  known  con- 
cerning the  reproductive  processes  such  an  homology  is 
unwarranted.  At  present  the  organism  is  only  known  to  re- 
produce by  division,  and  no  structures  have  been  discovered 
which  !u  ly  be  ideutitied  as  ova  or  spermatozoa.  Beueath  the 
upper  epithelium,  imbedded  in  the  cells  of  the  middle  tissue, 
large  refractive  spheres  (Fig.  30,  B,  r)  and  yellowish-green 
botrvoidal  masses  (/<)  occur,  but  they  have  apparently  no  con- 
nection with  reproduction. 


TRICHOPL 


The  DicYEMiDiE. 

The  Dicyemidre  are  elongated  vermiform  organisms  whicli 
are  parasitic  in  the  renal  organs  of  the  Cephalopods.  The 
various  species  of  Bicyema  (Fig.  31)  vary  in  length  from 
0.5-7  mm.  and  are  all  very  simple  in  structure,  consisting  of 
a  single  elongated  central  cell  (Fig.  31,  C)  extending  from  one 
end  of  the  body  to  the  other  and  covered  by  a  number  of 
ciliated  cells  arranged  in  a  single  layer.  Some  of  these,  situ- 
ated at  one  end  of  the  body,  are  smaller  than  the  others  and 
mark  ofl"  the  anterior  extremity  ;  there  is  no  mouth  or  diges- 
tive tract  and  no  sense-organs. 

Keproduction  is  carried  on  by  the  develo})ment  of  germ- 
cells  (f/)  produced  by  the  divisi(m  of  tho  nucleus  of  the  cential 
cell  and  the  concentration  around  the  (uiclei  so  produced  of  ii 
portion  of  its  ])rotopliism.  The  development  of  these  germ- 
cells  is  ap{>areutly  parthenogenetic  and  no  male  Dicifcnia  is  as 
vet  known.  In  young  individuals  iii;:  f^orm-cclls  sngincnt  in 
the  interior  of  tlie  coitral  cell  and  give  lise  to  "vermiform" 


^ 


'-C 


mi{ 


TRICHOPLAX,  THE  DIGYEMID^  AND  ORTHONECTID^.       65 

embryos  (Fig.  31,  V)  similar  to  and  developing  directly  into  the 
adult  form.     Auotlier  form  of  embryo  is,  however,  produced 
by   older   individuals,  its  formation    being 
iiecompanied  by  a  peculiar  behavior  of  the 
germ-cells.      The  nucleus  of  each  one  first 
divides  into  two  unequal  parts,  the  smaller 
l)art  separating  as  a  paranucleus  and  under- 
going no  further  development.      The  germ- 
cell  now  segments,    and    an  embryo   (Fig. 
31,    e)    consisting   of    a    single    large   cell 
partially  surrounded    by   smaller  cells    re- 
sults.    The    smaller  cells  are    now  thrown 
off  and  separate  somewhat  from  each  other, 
and  the  larger  cell  repeats  the  segmentation- 
l)iocess,  the  smaller  cells  being  again  thrown 
off;  and  this  may   happen    three    or    four 
times,  the  result  being  the  production   of 
tliree   or   four    concentric  layers   of   small 
cells  surrounding   a    single    larger  one,  all 
lying  in  the  central  cell  of  the  parent.     The 
large    cell    undergoes   no   further  develojo- 
ment,  but    the  smaller  ones,  except   those 
of  the  last  generation,  develop  into  "  infu-  " 
soriform"  embryos  of  a  peculiar  and  com- 
l)licated  structure.     The  cells    of  the  last 
generation  develop  into  "vermiform"  em- 1^,     o,      „  ""^ 
l..:.yos  si,„ilar  to  those    f„„.,.l    i„    yo^/'^^'Z^^:')! 

l>lcyemids.  several       fiKures       by 

The  fate  of  the  '« infusoriform  "  embryos  c  -"0X1  cell 
1ms  not  been  deternnue;l.     Since  they  are  «- embryos, 
eihated  it  seems  not  imj>robable  that  they  .v  -  germ -eel  Is. 
serve  for  the  dissemination  of  the  species  '' =  "'"^•'-'usofceutial 
-ulits  transference  from  one   CephalopcKl  v  =  ::^,orm     e.n- 
l'"^t  to   another.      It    has,    iiowover,   been  bryo. 

suggested  that  they  may  develop  into  males. 

The    OjtTHONECTIDA. 

The    Orthonectids    are    i)arasitic   on    Echinod.M-n,^    .,p.1 
nuortean  worms  and  resemble  in  structure  the  JJicvemids 


«P--h- 


g 


.\ 


66 


INVEHTEBHA  TE  MOliPIIOLOG  Y. 


TmCIIOPLi 


the  ectoderm  cousistiiig  of  a  number  of  ciliated  cells  arranged 
in  a  single  layer  and  enclosing  a  mass  of  germ-cells  which 
correspond  to  the  central  cell  of  JJicyeina.  Between  the  germ- 
colls  and  the  ectoderm  fine  nucleated  fibres  occur  which  are 
presumably  muscular. 

Three  forms  of  individual  are  known  to  occur  in  the  genus 
Ithopalura,  one  being  a   male,  and  the  other   two   females. 


Fig.  d2.—R7iopnhira  Oiardu  (nftM- Ji-un). 
A,  mule  ;  D,  round  fomule  ;  C,  flat  I'euifile. 

The  male  (Fig.  32,  .1)  is  about  half  the  size  of  the  females, 
which  measure  about  0.'^'  mm.  in  length,  and  presents  a  met- 
americ  arrangement  of  the  ectoderm  which  does  not  extend  to 
the  internal  cells.  The  cells  of  the  anterior  segment  havo 
their  cilia  directed  anteriorly-,  and  are  succeeded  by  a  segment 
consisting  of  several  rows  of  small  non-ciiiated  cells  eacli 
containing  a  refractive  body,  and  behind  this  there  follow  throo 
or  four  segments  formed  of  cells  provided  with  cilia  directed 
backwards.  One  of  the  female  forms  (Fig.  82,  B)  is  eloii 
gated,  and  is  segmented  like  the  male  oxce])t  that  the  segments 
are  more  numerous  and  the  second  non-ciliated  seynifint.  (>in\- 
sists  of  a  single  row  of  cells  destitute  of  refractive  bodies. 


TlilCHOPLAX,  THE  DIOYEMID^  AND  ORTllONECTIDJE.       67 

The  other  female  (Fig.  32,  G)  is,  on  the  contrary,  ovoid,  flat- 
toned,  and  unsegmented,  beiug  ciliated  all  over ;  it  differs 
furthermore  from  the  elongated  female  in  possessing  on  one 
side  near  the  anterior  extremity  a  granular  niass  containing  a 
large  nucleus  whose  significance  is  entirely  problematical. 

Associated  with  the  difference  of  form  of  the  two  females 
there  is  a  difference  of  function.  In  the  elongated  form  when 
the  ova  are  mature  the  anterior  two  segments  si)lit  off  as  a 
cap  and  allow  the  ova  to  escape,  and,  on  fertilization,  these 
^ive  rise  to  males.  In  the  ovoid  form,  however,  the  ova  are 
imbedded  in  a  gelatinous  mass,  and  are  liberated  by  the 
breakiug  up  of  the  parent  into  a  number  of  fragments;  from 
the  ova  females  of  both  forms  develop. 

The  systematic  position  and  affinities  of  the  Dicyemidfe  and  Orthonee- 
iidif  IS  a  mutter  of  uncertainty.  Tliey  i.ave  been  held  by  some  authors  to 
IM.SS..8S  atH.mies  witii  tiie  Greg.-vri.iida  and  by  otliers  to  be  degenerate  Ihit 
worms,  vvliile  others  iiave  sought  to  trace  resemblances  to  the  Rotifers 
llie  granular  mass  with  the  large  nucleus  which  occurs  in  the  ovoid 
RhopaUira  has  been  supposed  to  represent  a  rudiment  of  a  digestive  tract 
while  the  superficial  metamerism  of  the  male  and  elongate  female  of  the 
Orthouectida  may  possibly  point  to  a  derivation  from  more  highly  organ- 
ized aace:^trai  forms.  There  can  be  but  little  doubt  that  the  Dieyemidiel.nd 
Ortiioiiectida  are  closely  related,  but  at  present  sufflcienc  evidence  is  want- 
ing to  warrant  any  detinite  conclusions  as  to  their  relationships  to  other 
torms. 

LITERATURE. 

TRKIIOPLAX   ADn.KRENS. 

F.  E-  Schulze      Uher    Tnehnph,v  adhanrm.      Abhandl,  Akad.  Wiss.  Berlin. 
1»'J1  (see  also  /oolog.  Anzeiger,  vi.  1883). 

DKYEMID^. 

C  0.  Whitman      A   Contnhutiou  to  the  Emhr},olorn,,  Life-history,  and   aa.xi- 
J>«,ttoa  oj  the  Bwyemtds.     Mitth.  a.  ,1.  Zool.  Station  zu  Neapel.  iv.  1882. 

OKTIIONECTinyE. 

C.  JuUn^    Contribution  a  I'histoire  des  Mesozoairea.     Arcliives  de  Biologie.  iii. 


^IStjl 


«8 


IN  VEHTEBltA  TE  MOliPHOLOG  Y. 


CHAPTER  V 


TYPE  CaaENTERA. 


The  Coeleiitera  iwcliKlo  the  (li])h)Wastic  Metnzoji,  ouly 
two  gerin-hiyei'.s,  the  ectoderm  and  eudodenn,  being  re})re- 
seuted  in  tlieir  organization  (Fig.  83).     Between  these   two 

hiyers,  Iiowever,  a  third  (Fig.  38,  mg) 
is  invariably  present,  which  in  its 
primitive  condition  is  not  cellular,  but 
consists  of  a  gehitiuous  or  fibrous  sub- 
stance secreted  by  one  of  the  two 
cellular  layers.  Usually,  however, 
cells  from  the  endoderm  or  ectoderm 
wander  into  it,  and  sometimes  are  so 
numerous  as  to  give  it  the  appearance 
of  a  cellular  layer.  Even  in  such 
cases,  however,  the  gelatinous  matrix 
is  the  fundamental  substance  of  the 
Tig.  33.— Diagham  op  Hy-  layer,  which    it    seems    preferable   to 

lira  TO  snow  t.ik  Gen-  term  the  7/ie6<o;7?«;fl,  rather  than  to  imply 
EUAL    Stuuctuke    OF    a  ,  1  1  •   1      T  .       1  ' 

CasLENTEUATE.  ^"  liomology  which  does  not  exist  by 

ec  —  eciodenn.  designating  it  the  mesoderm. 

«»  =  endoderm.  In    consequence    of     the    absence 

y«^  =.- lucsoglavi.  of    ^i^e    mesoderm    the    Codenterates 

present  in  the  interior  only  a  single  cavity.  Consequently 
it  may  be  said  that  the  ccelom  is  not  represented  in  the 
Cffileutera,  though  their  central  cavity  is  usually  regarded 
as  equivalent  to  both  C(xdom  and  euterou  of  the  higher 
forms.  The  so-called  endoderm,  however,  seems  to  be  homol- 
ogous with  their  mesoderm  plus  endoderm,  and  may  be  more 
ac'jurately  termed  the  mes-ondoderm,  and  it  seems  preferable 
to  regard  the  ccelom  as  not  yet  differentiated. 

Another  feature  which  obtains  throughout  the  group  is 
the  radiate  ground-form.     In  many  but  one  axis  can  be  do- 


TYPE  COiJLENTBliA.  69 

termined  and  in  the  Spouj^es  the  form  may  become  so  irreLni- 
l;u-  tliat  thay  may  be  considered  to  be  destitute  of  axes  I„ 
«uch  forms  as  the  Medusa",  however,  a  typical  radiate  form 
occurs,  there  being  two  or  more  similar  axes  at  right  angles 
to  the  vertical  one  and  throughout  the  higher  members  of 
he  group  tiis  radiate  symmetry  is  more  or  less  apparent, 
though  It  becomes  decidedly  obscured  in  certain  AnthcLa  bv^ 
a  pronounced  tendency  towards  bilatorality,  which  in  a  few 
forms  {Urianthdw)  actually  replaces  it 

In  correspondence  with  their  low  grade  of  general  struc- 
ture there  is  no  very  extensive  differentiation  of  tissues      A 
considerable    degree  of   division   of   labor  of   course  occurs 
among    he  cells,  and  cells  having  the  same  function  may  be 
aggregated  together  so  as  to  form  a  somewhat  definite  tissue 
as  m  the  case  of  the  nerve,  muscle,  and  reproductive  cells,  bu 
even  m  these  tissues  there  seems  to  be  a  considerable  an.ount 
ot  mdividuality  retained  by  the  constituent  cells,  and  the  tis- 
sues  can  only  be  regarded  as  exceedingly  diffuse.     Of  or-ans 
except  in  some  colonial  forms  with  division  of  labor  amon.: 
he  constituent  individuals,  it  is  hardly  correct  to  speak,  th^ 
Ca.lonterates  not  having  progressad  beyon.l  the  organ  stage 
oi  individuality.  " 

The  type  Celentera  may  be  divided  into  two  subtvpes, 
the  Ponfera,  or  Sponges,  and  the  Cnidaria.  ^ 

I.  Subtype  Porifera. 

The  Sponges,  on  account  of  their  fixed  life  and  irregular 
for.n  were  long  regarded  as  plants,  and  it  is  only  within  com- 
paratively recent  times  that  their  true  relationships  have  been 
ascertained.  They  are  almost  exclusively  marine  in  llbi^It 
occurring  m  large  numbers  in  the  warmer  seas,  and  inhabit 
the  ocean  depths  as  well  as  the  shallower  waters.  A  few 
Keuera,  e.^  Spongilla,  Ephyatia,  represented  by  numerous 
•species,  are  inhabitants  of  fresh  water. 

C}]inder  fixed  at  one  end,  while  at  the  other  is  an  opening- 

tlie  osculum,  and  scattered  over  the  surface  of  the  cylindei- 

I  are  a  numuer  of  smaller  openings, ;.-o.opy/^..     Throug'h  these 


I 


70 


INVERTEBRA TE  MORPHOLOO  T. 


water  passes  iuto  the  central  cavity,  the  coelenteron,  and 
escapes  by  the  osculum.  The  exterior  of  the  body  is  covered 
by  a  layer  of  flat  cells,  the  ectoderm,  and  the  c(jeleuteron  is 
lined  by  collared  cells  provided  with  a  single  flagellum  and 
resembling  greatly  Autoflagellata  bek)ngiug  to  the  genus 
Codosiga.     These  cells  constitute  the  eudotierm,  and  between 


OS 


.5^   \ 


Fig.  34 —An  Ascon 
SjroNCiK,  A^iCcUwpri- 
monliaLiH  uiriej'  Hak- 
CKKi,  from  yoLLAS). 


Fig. 


35.  —  Diagram    to    show   the  General 
Structure  of  a   Sycon  Sponge. 
The  upper  porliou  represents  the  simplest  cou- 
ditiou,  the  complexity  increasiug  downwards. 
cc  =  ciliated  chamber.  ic  =  iuhalent  canal, 

Os  —  osculum.  p  —  iuhalent  pore. 

pr  =  prosopyle. 

it  and  the  ectoderm  is  the  mesogloea,  in  which  are  imbedded 
large  numbers  of  cells,  giving  it  almost  the  appearance  of  a 
cellular  layer. 

In  such  simple  Sponges  the  mesogloea  is  comparatively 
thin  and  the  pores  open  almost  directly  iuto  the  coelenteron 
lined  by  the  collared  cells.  This  arrangement  constitutes  the 
first  or  Ascon  type  of  structure.  In  the  majority  of  forms  a 
much  greater  complexity  arises  from  the  Avails  of  the  simple 
cylinder  being,  as  it  were,  drawn  out  into  a  number  of  finger- 
like processes,  each  of  which  communicates  by  a  wide  open- 


TYPE  CCELENTEIiA. 


71 


iiiK  with  the  cavity  of  the  orij^inul  cylinder  (Fig,  35).     The 
cells  liuiug  the  central  cavity  become  flattened,  the  collared 
cells  being  found  only  in  the  interior  of  the  secondary  cylin- 
ders which  radiate  from  the  central  chamber  {cc).     Pores 
termed  prosopyles  {pr),  occur  in  the  walls  of  the  secondary 
cylmders,  which  are  closed  at  their  free  ends.    Through  these 
prosopyles  water  passes  into  the  interior  of  the  radiating  cyl- 
inders, thenoe  into  the  central  cavity  and  so  to  the  exterior 
by  the  osculum.     Further  complication  occurs  by  the  walls 
of  the  radiating  cylinders  coming  in  contact  with  each  other 
iiad  fusing  in  a  more  or  less  irregular  manner,  the  space  be- 
tween the  various  cylinders  being  thus  divided  into  a  series 
of  more  or  less  well-defined  inhalent  canals  {ic)  into  which  the 
water  passes  through  pores  {p)  which  lie,  morphologically,  be- 
tween the  extremities  of  the  radiating  cylinders.    The  cavities 
of  these  cylinders  now  form  the  ciliated  chambers,  and  Sponges 
111  which  they  possess  the  cylindrical  form  are  said  to  belong 
to  the  Sycon  type.     The  annexed  diagram  (Fig.  35)  illustrates 
the  (lifferent  stages  of  complexity  met  with  in  Sycon  Sponges. 
The  next  complication  consists  of  the  branching  of  the 
ciliated  chambers,  though  they  still  retain  a  cylindrical  shape, 
aud  their  separation  from  the  central  cavity  by  a  tract  lined 
with  flattened  cells  (Fig.   36,  A)  ;    and  finally  the  collared 
cells  become  limited  to  a  portion  of  the  radial  chambers. 
the  ciliated  canals  thus  becoming  circular  in  shape  and  united 
Avith  the  central  chamber  by  long  and  rather  slender  canals 
hued  with  flattened  cells  (Fig.  36,  B).     This  constitutes  what 
IS  termed  the  Leiicon  type   of  structure.     In  this  type  the 
pores  upon  the  surface  of  the  Sponge  frequently  do  not  open 
jinectly  into  the  canals   leading  to   the  ciliated  chambers, 
hilt  into  a  wide  lacunar  cavity,  the  suhdermal  space,  lying  be- 
low the  cortical  layers  of  the  sponge,  and  with  this  the  canals 
communicate. 

To  these  complications  of  arrangement  further  complexity 

IS  added  by  the  occurrence  in  many  Sponges  of  what  may  be 

consulered  budding,  in  some  cases  leading  to  the  formation 

0    (lehnite  branches,  or  in  others  producing  only  a  number 

I  of  oscula,  each,  however,  with  its  own  canal  system.. 

The  general  characteristics  of  the  ectoderm  and  endoderm 


72 


INVERTEBRATE  MORPHOLOGY. 


have  been  indicated  iu  the  preceding  description  of  the  canal 
systems ;  the  mesoglcjea  requires,  however,  further  notice.  It 
consists  of  a  gelatinous  matrix  which,  however,  contains  lar^^e 
numbers  of  cells  presenting  a  considerable  amount  of  dif. 
ferentiation.  Some  are  amoeboid  in  form,  others  contain  pij^. 
ment,  others  again  are  elongated  and  spindle-shaped,  formiL<r 
the  contractile  cells,  others  form  the  reproductive  elements, 
ova  and  spermatozoa,  while  others  again  are  skeletogeuous 
in  function,  well-developed  skeletal  structures  being  present 


Pig.  36.— Two  Figures  showing  Differences  in   rnE  Complexity  of 

Stuuctuue  of  a  Lel'con  Sponge. 

A.  LeuciUa  (Iter  {Atiw  DfLwyy,  B.   OHcarella  lohul(irin  ^AfwvUcnvi.zK). 

ce  =  ciliated  cliamber.  p  =  iulmlent  pore.  sp  =  spicule. 

in  almost  all  Sponges.  In  some  f()rms  the  skeleton  preseuts 
the  lV)riu  of  siliceous  spicules  either  of  a  simple  needle-like 
form,  oi-  presenting  mtnlilications  of  a  four-  or  six-rayecl 
ground-form,  or  finally  assuming  the  form  of  hooks,  anchors, 
or  spiny  spheres.  In  auother  group  there  is,  associated  u.su- 
ally  with  needle-like  siliceous  spicules,  a  network  of  a  horiiv 
material  termed  HpongloUn  which  forms  a  sup[)ortive  scafl'old- 
ing  for  the  st)ft  parts  of  the  Sponge,  and  lastly,  iu  anotli.-i 
group  the  spicules  arn  c(Mni»i)sed  of  carbimate  of  lime  ami 
present  a  variety  of  forms  \  Fig.  3G,  A). 


s  caual 

36.       It 

i  large 
of  dif. 

iu   pifr. 

iieuts, 
euous 
reseut 


CJC 


ITV   (IF 


TYPE  C(ELENTERA.  73 

Nerve-cells  have  also  been  described,  though  a  definite 
nervous  systen.  cannot  be  said  to  exist.  ElongaLl  re'rcf  le 
processes  have  been  observed  projecting  from  the  sur^acl  of 
cer tan.  sponges  ana  at  the  base  of  each  is  a  group  of  st  L te 

liepio  ess      lo  these  cells  a  nervous  function  has  been  at 
tn  juted  and  the   processes  have  been  considered  senTory 
-Ih  the  exception  of  these  structures,  however,  no  sense' 
organs  or  nerve-elements  have  been  yet  observed. 

llie  Sponges  may  be  arranged  according  to  the  nature  of 
then-  skeleton,  in  four  orders.  ^auire  ot 

1.  Order  Calcarea. 
In  the  Calcarea  the  skeleton  is  always   r>rP««nf         i    • 
formed   of   spicules   consisting   of   carbonil'oTte      Th: 
group  contains  forms  of  various  comnlpvi-fv^^    /     \         , 
U.   simple    cylindrical    /.  J:!^ tl^tn  ^ l;;::;.^^ 
Ascoatype  through  Sycon  forms  such  as  OmntiauZ 
sentutives  of  the  third  and  fourth  types.     Imleed  ft  i    o     ' "" 
this  group  that  the  Ascon  and  Svcon  tvnesof  .h     7    ^ 
found      AH   flm  v..  •      ^•>^""  t.^  pes  ot  structure  are 

sLViudeptL  '■"  "''"'"  ""  '""""^  "■">  '-■«  "'  only 

2.  Order  Cornacuspongise. 
{        The   skeleton  of   the  Cornacuspougiro  consisf.,  «,-fl  <• 

;   sihceous,needle.liI<e  spicules,  fre^plent^^^mr^e^^tl^t: 
in-  simngiolm,  or  else  entirely  of  a  network  nf  T 
posed  of  the  latter  substance."^  Like  th         Uca         T  '""" 
i»imbitants  .>f  shallow  M-ater  and  are  n,'  T       ^'"•''  '''^ 

1-HlH   upon   the   entire   absence   J    H^^' ^^^^^^^^  ^^'■ 

^vi'ioh  is  found  in  the  shallo      4t    s  I       ?'""^'"'  '"^^ 

of  the   MeditGrran«n..    ,-..  t^      p  "f  "  ^  ""'*"'"  I"*'^'"" 


^Bi 
^^^" 


74 


m VERTEBRA  TE  MORPHOLOQ  7. 


3.  Order  Spiculispongise. 

The  skeleton  in  the  SiDiculispougiae  is  occasionally  entirely 
wanting,  as  in  the  genus  JIalisarca,  but  usually  consists  of 
siliceous  spicules  usually  tetraxial  or  rod-  or  club-shaped, 
sometimes  interlocking  with  one  another  so  as  to  form  a  firm 


Fig.  37.— a  small  Spongilla  with  oNiiV  a  single  Osculum  (from  Huxlkv). 
a  —  iiilialenl  pore.  c  =  ciliuted  clianiber  seen  through 

d  =  oscuUini,  tlie  tissues. 

skeleton-  One  of  the  members  of  the  group  is  the  **  boviu*,' 
sponge,"  CUona,  which  excavates  channels  in  and  assists  iu 
the  disintegration  of  oyster-shells,  frequently  attacking  tho 
idiells  of  living  animals  and  contributing  to  their  destruction. 


4.  Order  HyalospongisB. 

The  Hyalospongiw  are  essentially  deep-sea  forms,  and  are 
characterized  by  the  possession  of  six-rayed  siliceous  spicules 
as  skeletal  elements.  The  spicules  inuy  becomt>  fused  to- 
gether to  form  a  firm  siliceous  network  having  the  appear- 
ance of  spun  glass,  as  in  the  genus  Eupleciella,  commonly 
known  as  Venus'  Flower-basket. 

Reproduction  of  the  Porifern. — Soxiia]  reproducfcion  occur* 
])robab]y  tliroughout  the  entire  group  of  tho  S])ouges,  the  nv 


TTPE  CaSLEXTEHA.  n« 

rrodnctive  elements,   ova    and  spermatozoa,   differentiatm^ 
i.«m  mesosteal  cells     Many  Sponges  a.e  hemaph"  dte  t 
»,,«-,atozoa  developing  usually  somewhat  in  advluee  of'the 
«v..  but  some  forms  seem  to  have  separate  sexes      The  o™ 
an.  lertihzed  while  still  within  the  tissues  of  the  parent  and 
...HLngo  a  portion  ot  their  d6velopn,eat  there,  laterXelun^ 
t  n,ush  into  a  canal  and  so  passing  to  the  exterior  a    a  c  h 
.te,l  free-swimming    structure.      The    seixmentiti,,,,      f   . 
OV-.UI  iu  typical  eases  results  in  the  fo™S  '  '"abla  t.  1' 
"iuch  becomes  converted  into  a  solid  ciliated  steiruTalv 
"...ulgnition      After  swimndug  about  for  a  tim    t  e     terruH 
loses  Its  ciha  and  settles  down  a  c.,v,f>.  .,        "."'«.  s-'ei '  ula 
tenor,  which  later,  in  forms:!, tlt  ^o^^^,  'Sl^f  j:  ''^  '"" 
gives  rise  to  these  structures  as  a  .i  .^    f  "''ambers, 

tio.  with  which  canals  :-e      ■^"';:i^Zt^  '"'T' 

u  j^astrulu  results    ustejul  of  a  st^-  rnL,      Ti  .     , 

In  addition  to  the  sexual  method  most  Sponges  also  po, 

<-.    abilities  for  regenerathui.    A  detached  portion  of  ,.  •<, 

;n     under  favorable  conditions,  regeneia!:  i  '  L^''  :r 

I>i"'lnctiim  of  the  ommerc  a    Spouues      In  -n,,,,.  f,.. 
•■■•■I"-;;  '..  this  a  process  of  interl.al  t  ddi  ^        ursl ';:,:" 
;;;;■  ■;    '-'-"KI-:'!  ™"s  aggregating  together  r,dev: 
2  "■'"  '■ '  oval,  ciliated,  sterrnladike  structure  which  leaving 

•'"""■•••  •■*  - ' "'  ■i'>..... .1.1.1.  II,.  ,„,:;;;;ii 


I 

I 


76 


INVEHTEBHATE  MORPUOLOG  7. 


dividual  cannot  withstand.  Thev  are  spherical  bodies  con- 
sisting of  a  mass  of  cells  richly  laden  with  food-matter,  and 
enclosed  in  a  double  chitinous  wall,  with  an  opening  at  one 
point,  a  number  of  siliceous  spicules,  in  the  allied  genus 
iLphydatia  of  a  very  characteristic  form  and  known  as  amp/ii- 
discs,  being  arranged  between  the  two  layers  of  the  wall.  Ou 
the  approach  of  cold  weather  the  Sponge  dies  down  and  the 
gemmules  thus  fall  to  the  bottom  of  the  ponds  or  streams, 
where  they  remain  unchanged  until  the  approach  of  warmer 
weather,  when  the  internal  cellular  mass  flows  out  through 
the  pore  (which  is  closed  only  by  a  thin  membrane)  and  de- 
velops into  a  new  Spomjilla. 

The  relationslni)s  of  the  Sponges  have  long  been  a  matter  of  discussion. 
For  a  long  time  they  were  regarded  as  plants  and  later  as  colonies  of  Pro- 
tozoa, but  the  discovery  of  sexual  rei)foduction  in  them  and  of  their  mode 
of  development  demonstrated  that  they  were  to  be  considered  Metazoa. 
At  present  the  question  as  to  whether  they  are  to  be  associated  with  tlie 
Cnidaria  among  the  Ccelenterates  or  regarded  as  a  distinct  type  is  still 
open,  though  the  weigiit  of  evidence  and  authority  is  in  favor  of  their 
Cuilenterate  character.  8uch  simple  forms  as  Leucusolenia  certainly  point 
in  that  direction,  and,  if  tlie  occurrence  of  a  sterrula  formed  by  immigra- 
tion prove  the  typical  mode  of  development,  the  embryology  of  the  Sponges 
presents  stages  up  to  the  formation  of  the  ciliated  chambers  which  are 
step  by  step  comparable  to  what  occurs  in  the  Cnidaria. 


II.  Subtype  Cnidaria. 

The  Cnidaria,  like  the  S})onges,  liave  in  their  simplest 
forms  tlip  general  form  of  a  hollow  cylinder  open  at  one  end 
and  consisting  of  but  two  cellular  layers,  the  ectoderm  and 
endoderm,  between  which  is  interposed  a  tibrous  or  gelatinous 
mesoghva  which  may  or  may  not  contain  cells.  Differences 
from  the  S|)onges  are  found  in  the  occurrence,  exce])t  in  one 
or  two  forms,  of  a  number  of  elongated,  contractile  i)r()coss('s 
or  tentacles  around  the  mouth  of  the  cylinder  (see  Fig.  H^it, 
and  in  the  absence  of  inhalent  pores  upon  its  surface.  Sucli 
simple  forms  are  known  as  polyps,  and  they  are  usually 
attached  organisms  with  little  or  no  [)<)wer  of  locomotion.  V 
large  number  of  C^uiduria  present  u  very  different  form,  how- 
ever, Ix'ing  disk-  or  bell-shaped,  a  process  comparable  to  tlio 
cla})per  of  a  beil    hatiging  (hnvn  fnuu  tin?    centre  and  liav- 


TYPE  CWLENTERA.  77 

ii)g    at  its  extremity  the  mouth-opening.     This    leads    into 
u  central  cavity,  the  coelenteron,  lying  in  tlie  substance  of 
he  bell     and  Irom  this  pouches  or  iine  canals  radiate  out 
towards  the  rim,  where,  in  some  cases,  they  are  united  by  a 
circular  canal  which  runs  completely  round  the  bell  at  this 
region.     To  the  margin   of  the    bell    tentacles    are  usually 
attached,  and  sense-organs,   presenting    frequently  consider 
able  complexity  of  structure,  are  found  in  the  intervals  be- 
tween the  tentacles  or  at  their  bases.     These  forms,  known 
as  medusae,  are,  as  a  rule,  free-swimming,  propelling  them- 
selves through  the  water  by  vigorous  contractions  of  the  bell 
All  Cuidaria,  whether  of  the  polyp  or  medusa  form,  pos- 
sess in  their  tissues  peculiar  elements  altogether  i.urem-e- 


.-  cl 


t  - 


seated  in  the  Sponges.     These  are  the 
nematocysts    or     so-called     thread-cells. 
Each   consists  of   an  ow'.  or  spherical 
cyst  (Fig.  38,  c)  with  a  membranous  wall 
and  Hiiid  contents,  the  wall  being  pro- 
longed at  one  end  into  a  long,  exceed- 
ingly  delicate,  hollow,  thread-like  lila- 
iiK'iit  sometimes  furnished  with  sjiines  at 
its  base,  and,  in  an  undisturbed  cyst,  is 
invagiuated,  and  coiled  up  in  the  interior 
(Fig.  38,  t).     These  nematocysts  are  pro- 
duced  by  and  enclosed  within   special  Fig 

cells     known    as   cnidohhists   {en)   lying        .  ^  „_, 

principally  in  tlie  ectoderm,  and  in  their     "  ~  "enmtocyst. 
most   highly   developed    form   difr»n-en-    't  -  """'t','!'- 
tiuting  below  into  a  supporting  stalk  (.)  Z  Z  r^'il^.^ation 
wliu'li  rests  upon  the  outer  surface  of     «  =  Mi|,,„„ti„g  process, 
the  luosogloea.     From  the  outer  extreini-     '  "^  ""■*^'''"'- 
ty  there  projects  l^evon,!  the  surface  of  the  ectoderm  a  short 
i.nr-likeproce^  ,.:.  cnidocU(cl),^n^,  iu  addition,  an  excoe.ling- 
y  hno  process  of  Kn.e  length  («)  is  given  oti"  at  the  juncti,;n  of 
tlio  stalk  with  the  cyst-co)>taiuing  portion  uf  the  cell      The.se 
two  processes  a/e  supposed  to  be  sensitive,  the  longer"ono  per- 
mj.s  bringing  the  cni,lob!ast  into  connection  with  nerve-cells 

lying  elsewiiore 'u  the  ectndHrtp      Tm -i-m ^ 

eily  uuderHt<.od,  a  stimulation,  such  us  a  touch  by  some  foreign 


38.  —  Nematooyst 
Cell  of  Phyaalia. 


»«.x. 


78 


IN  VERTEBRA  IE  M0RP110L06  Y. 


body,  produces  au  evagiuation  of  the  coiled  thread  from  the  cj'st, 
ill  the  interior  of  wliich  it  has  been  bathed  hy  the  fluid  contents. 
The  evagination  is  of  suflicient  force  apparently  to  puncture  the 
skin  of  many  animals  and  so  inoculate  the  contents  of  the 
cyst,  which  are  of  a  poisonous  nature,  and  produce  inflam- 
iiiutory  disturbances,  and  in  minuter  organisms  paralysis  or 
death.  To  the  presence  of  these  structures  jelly-iishes  owe 
their  stinging  powers,  and  they  form  eflicient  weapons  both 
for  obtaining  food  and  for  warding  ofl'  enemies. 

The   Cnidaria   may   conveniently   be  divided   into   three 
classes : 

I.  Class   Hydromedusce. 
II.        "      Scyphoine^  'us<x. 
III.        "      Anthozoa. 


i.  Class  HYDROMEDUsa: 

The  Hydroraedusa3  present  both  polyp  and  medusa  forms, 
the  members  of  'me  of  the  orders  contained  within  the 
class  being  only  of  the  medusa  form,  while  in  another  order 
only  the  polyp  form  occurs.  Usually,  however,  both  forms 
occur  in  more  or  less  perfect  development,  representing  two 
stages  in  the  life-history  of  an  individual  and  succeeding  one 
another  in  the  definite  manner  which  has  been  already 
described  as  au  alternation  of  generations.  The  polyps  pos- 
sess the  power  of  non-sexual  reproduction  b^^  budding  ami 
give  lise  by  this  method  not  only  to  medusa?,  but  also  to 
■other  I'olyp  individuals  which  ma}'  remain  in  connection  witli 
■one  another  and  thus  give  rise  to  branching  colonies.  As  a 
rule,  the  medusa  individuals  separate  from  the  polyp  and 
lead  a  free  life,  but  in  the  order  Siphonophora'  they  may 
remain  in  connection  with  each  other  and  with  polyp  individ- 
uals, undergoing  various  ada"^  tations  of  form  in  accordance 
with  dift'erent  functions  which  they  assume,  the  whole  form- 
ing a  colony  presenting  in  a  high  degree  a  division  of  labor 
among  the  c()mi)onent  individuals. 

As  has  already  been  point'd  out  the  structure  of  the  polyp 
form  difl'ers  considerably  from  that  of  tiie  medusa.  The 
polyp  is  more  or  less  eyliiidricai  in  foiiii,  taperiug  oil  above 


TYPE  CCELENTERA. 


79 


so  that  the  free  eud  has  a  somewhat  couical  shape,  the  month 
bems  situated  at  the  end  of  the   coue.     At  the  base  of  the 
coue,  which   is  termed  the  hypo. 
■stoine,  there  is  usually  a  circle  of 
tentacles,      though      occasionally 
they  are  scattered  irregularly  over 
the  surface  of  the  hypostome,  and 
a  second  circle  of  tentacles  may 
be   present  at    the    base  of   the 
jiolyp    (Pennaria).      In     colonial 
forms  each  individual  [hydranth) 
(Fig.  39,  hy)  is  situated  at  tue  ex- 
tremity  of  a  stalk  or  hydrocaulv^s 
ilic),    the    various    stalks    either 
uuitmg  together  to  form  a  branch- 
iug  colony  or  else  arising  from  a 
uetwork,    the    hydrorhiza,    which 
covers  the  surface    upon    which 
the  colony   grows  ;    or   occasion- 
ally  each  hydranth  arises,  with- 
out the  interventi(m  of  a  hydro- 
caul  ua,    from     a     tiat     plate-like 
expansion    common   to    all.      In 
either    case    the    coelenteron    is 
coutiuuous  throughout  the  endie 
colony,  the    fleshy   substanco    of 
the  hydrocaulus  and  hydrorhiza, 
<:(xnosarc  {co),  being  tubular  and  in 
•lirect   continuity  with  tlie  body- 
Halls   of    the    hydranths.       The 

^u.uosarc  is  enclosed  within  a  chitinous  substance  termed  the 
/-'•-or  (p)  secreted  by  the  ectodernuU  cells  and  sometimes 
I -louged  at  the  end  of  each  hydrocaulus  into  a  eup-like 
J^tnu.ture  theMr.^/.x.«  {ht),  into  which  the  hvdranth  may 
I'  retracted  ;  occasionally  this  ectodermal  secretion  takes 
the  form  of  carbonate  of  lime. 

The  ectoderm  generally  shows  a  considernble  amount  of 
^btb.rentiatiou  of  its  constituent  cells.  In  addition  in  fl.e 
nn.iuOM^ls^  which  have  been  already  describ..,] 


-go 


Fig,  39.— Portion  of  a  Colony 
OP  THE  Campanulaiuan  Hv- 
DBOiD  Clytia 

CO  =  coBiiosarc. 

he  =  liydroc'Hiilus. 

ht  =r  liydrollieca. 
hy  =  hydniiitli. 
go  =  fonotlieca. 

m  =  iiioiilh. 

p  =  peiisarc. 
t  =  tentacle. 


;*i 


'taie»»MiMni»i«Mtm', 


80 


INVERTEBRATE  MORPJIOLOGY. 


Fig.  40.—^  =  Epithelio- 
muscular  cell  of  Ca'leu- 
terate  ;  B  =  musciiliir 
cell ;  U  =  seusory  cell. 


lio-muscular,  muscular,  glandular,  and  nerve  cells  are  gener- 
ally to  be  found  in  it.  The  epitlielio-muscular  cells  (Fig.  40, 
A)  are  the  most  numerous  and  consist  of  columnar  cells,  one 

extremity  of  which  bears  a  cilium  and 
helps  to  form  the  outer  surface  of  the 
body,  while  the  other  is  prolonged  into 
a  somewhat  spindle-shaped  process  of 
highly  contractile  muscular  substance. 
The  muscle-cells  (Fig.  40.  B)  are  modi- 
fications of  these,  having  lost  their 
connection  with  the  surface  of  the  body, 
the  cell-protoplasm  and  nucleus  form- 
ing a  small  elevation  on  the  muscle- 
fibre.  The  muscle-fibres  rest  upon  the 
outer  surface  of  the  mesogloea,  and  in  the  ectoderm  are,  as  <i 
rule,  arranged  longitudinally,  so  that  by  their  contraction 
they  cause  a  shortening  or  retraction  of  the  polyp.  The  nerve- 
cells  are  of  two  kinds :  (1)  seusory  cells  (Fig.  40,  C),  which  are 
slender  cells  whose  free  end  bears  a  single  cilium,  while 
the  inner  end  is  jDroduced  iuto  one  or  more  slender  nerve-proc- 
esses which  are  supposed  to  place  tliebo  cells  in  conuectiou 
with  (2)  the  gfuiglion-cells.  These  are  stelluto  cells  lying  in 
the  dee})er  layers  of  the  ectoderm,  just  external  to  the  muscle- 
cells,  and  sending  off  delicate  processes  in  various  directions 
so  as  to  form  a  plexus  of  nerve-fibres  ramifying  through  the 
ectoderm. 

The  mesogloea  is  thin  and  more  or  less  fibrous  in  structure, 
and  rarely  contains  cells.  The  endoderm-cells  are  large  and 
are  of  the  epitlielio-muscular  variety,  tlie  muscle-fibres  hav- 
ing a  circular  arrangement  producing  by  their  contraction  a 
diminution  of  the  diameter  of  the  polyp.  The  protoplasmic 
])ortion  of  each  cell  is  furnished  with  a  single  flagelluni  and 
is  digestive  in  function,  taking  food-particles  into  its  sub- 
stance and  there  digesting  them.  In  addition  to  these,  glaml- 
ular  cells  also  occur  in  the  endoderm,  especially  in  the  region 
of  the  hypostome. 

The  medusa  forms  have  the  shape  of  a  bell  (Fig.  41' 
which  may  be  either  shallow  oi  deep,  the  mouth  of  the 
bell  in  all  cases  being  partially  cloHtMl  })y  a  fold  of  tb 


IMSUC 


TYPE  C(ELENTEIiA.  gj 

which  projects  from  the  rim,  and  is  known  as  the  velum, 
rom  the  presence  of  this  structure  these  medusae  have  been 
termed  cm^ecZo^e  medusa..  The  cavity  between  this  and  the 
bell  is  ihesuhumhrellar  cavity,  into  which  projects  a  process 
corresponding  to  the  clapper  of  the  bell  and  termed  the 
manuhnum.  At  the  free  end  of  this  is  the  mouth,  which 
opens  into  a  canal  traversing  the  manubrium  and  communi. 
catmg  at  its  base  with  the  gastric  cavity  lying  in  the  «ub 
stance  of  the  bell.  From  this  four  (in'soL^ases  ^re)' 
canals  or  pouches  radiate  out  towards  the  rim  and  com- 
municate  there  with   a  circular  canal   which  extends   com. 


Fig.  il.—Liriope  mit/gera  (after  Brooke). 


joins  It.     1  he  caaal  of  the  niaimbiium.  the  {-astrie  cavitv 
an    t  e  raJiatiug  aucl  ci.-e„la,.  canals  together  co.sttute  te' 
«louterou.     T„  the  margin  of  the  bell  tentacles,  v.     ■  n,    n 
nmnher,  are  generally  attache,!,  „„  or  between  the  bases"  o^' 
nliicli  seuse  organs  are  to  be  toii]„l. 

The  mednsm  ,lWer  not  only  in  form  bnt  also  in  habit  from 

I     Iv  rr'  '"',"'«/'■»■»""■■»""«  m-ganisms,  propelling  them. 

s  thmngh  the  water  by  expelling  the  water  from  t  "e 

.unabrellar  cavity  through  the  velar  opening  by  snck  en 


■X      iiiU 


sense-organs  are  present,  and  a  ijifrl,er 


82 


IN  VERTEBRA  TE  MORPHOLOO  7. 


development  of  the  nervous  system  tlian  is  found  in  tlie 
polyps  obtains.  The  sense-organs  vary  both  in  structure  and 
function  in  different  medusa3,  in  some  being  spots  of  pigment 
sometimes  provided  with  a  refractive  lens  and  functioning  as 
light-percipient  structures.  Such  medusae  (Fig.  45)  are 
termed  ocellate,  or,  since  the  eyes  are  on  the  surface  of  the 
bell  and  are  not  enclosed  within  a  chamber  formed  by  the 
growth  around  them  of  the  adjoining  tissues,  they  are  some- 
times  termed  gymnophthalmatous.  In  other  forms  again  the 
sense-organs  consist  of  a  group  of  cells  containing  in  their 
interior  crystals  of  carbonate  of  lime  and  having  a  somewhat 
vesicular  appearance,  and  in  the  neighborhood  of  these  are 
sensory  cells  with  long  stiff  cilia  to  which  are  imparted  any 
vibrations  which  the  crystals  may  manifest.  Such  crystal- 
containing  cells  are  known  as  otocyst\  on  the  supposition  that 
they    form   auditory  us,    but   it    seems   more   probahle 

that  their  function  is  of  equilibrium  organs,  informing 

the  medusae  of  their  p,  ^ition.  Medusae  possessing  such 
organs  (Fig.  43)  are  termed,  to  distinguish  them  from  ocelhite 
forms,  vesiculate  medusaB. 

The  ectoderm  which  covers  the  outer  surface  of  the  bell  is 
much  flattened,  but  near  the  rim  it  becomes  columnar  and 
is  ciliated,  some  of  the  cells  assuming  the  form  of  sensory 
cells  similar  in  appearance  to  those  of  the  polyps,  their 
slender  nerve-Hlaments  forming  a  delicate  plexus  in  the 
deep  r  layers  of  the  ectoderm,  in  which  are  here  and  there 
imbedded  stellate  ganglion-cells.  A  special  nerve-ring  sur- 
rounds the  bell  at  its  margin.  The  ectoderm-cells  which 
cover  both  surfaces  of  the  velum  and  the  subumbrellar  surface 
are  of  the  epithelio-muscular  and  muscular  types,  the  mus- 
cle-fibres being  for  the  most  part  arranged  circularly.  In 
the  deeper  layers  of  the  subumbrellar  ectoderm  numerous 
ganglion-cells  with  long  prolongations  occur  forming  a  net- 
work immediately  external  to  the  muscle-processes,  and  at 
certain  definite  regions  collections  of  reproductive  cells  occur, 

The  mesoglcea  of  the  subumbrellar  surface  and  of  the 
velum  is  thlu,  resembling  that  of  the  polyps,  but  in  the  convex 
portion  of  the  bell  it  is  very  thick  and  gelatinous  in  texture,  and 
may  in  soiue  cases  contain  cells.    The  eudoderm  is  throughout! 


form  after  a  c 
I  tion  also  occurs 
I  a  little  below  tl 
[same  layer  son 
[being  hermapli 
jimbedded  in  tlj 
[later,  developin, 
jof  the  water,  an 
[developiug  furtl 
jstaud  a  consid( 
jmay  tide  the  sp< 
[stage  occurs  in  . 

ffylra  grisea  L 
hiridis  L.  is  smaller 
(ing  corpuscles  imb 
fiutiiors  to  be  unicel. 


TYPE  COS  LENT  ERA.  83 

tl.e  ccBlenteron  ciliated  ;  in  tlie  tentacles,  which  may  be  either 
hollow  or  solid,  It  may  retain  its  ciliated  character,  or  else  in 
•l.B  solid  tentacles  form  a  solid  axis  similar  to  that  of  the 
tentacles  of  the  polyp  forms. 

Siich  are  the  general  structural  features  common  to  all 
the  Hydromec  us*.  It  remains  to  add  here  certain  points  by 
which  especially  they  are  distinguished  from  other  groups  of 
Cuulana  hese  are  :  (a)  the  ectoderm  and  endoderm  meet  at 
the  mouth-opening  ;  (b)  the  sense-organs  when  present  are 
iiever  modifaed  tentacles:  (c)  a  velum  is  always  present  in  the 
medusa  forms ;  and  {d)  the  reproductive  elements  have  their 
origin  in  the  ectoderm. 

1.  Order  Hydrarise. 

To  this  order  belongs  the  Hydra,  a  common  inhabitant  of 
fresh-water  ponds  and  streams  in  all  parts  of  the  world      It 
IS  a  simple  cylindrical  organism,  adherent  by  one  extremity 
to  foreign    bodies,   though  not   fixed,   being  "able   slowly    To 
change  its  position.     Below  the  short  hypostome  is  a  single 
row  of  exceedingly  extensible  tentacles,  which  are  hollow  a 
peculiarity  found  in  no  other  Hydromedusan  polyps.     So  loL 
as  conditions  are   favorable  an.l  nutrition  abun<lant  llmlm 
reproduces  by  budding,  the  buds  separating  from  the  parent 
orm  after  a  certain    period    of  growth.     Sexual    reprod.ic- 
lon  also  occurs,  the  spermatozoa  developing  in  the  ectoderm 
a  httle  below  the  ring  of  tentacles,  while  the  ova  form  in  the 
same  layer  somewhat  lower  down  on  the  body,  the  animals 
being  hermaphrodites.     The  ova   after  fertilization   remain 
mbedded  in  the  ectoderm  of  the  parent  for  some  time,  but 
later,  developing  around  them  a  cyst,  they  sink  to  the  bottom 
of  the  water  and  there  remain  usually  for  some  time  without 
leveloping  further.     In  this  condition  they  are  able  to  with- 
taud  a  considerable  amount  of  cold  and   dryness,  and  so 
jr.  a;  tide  the  species  over  unfavorable  conditions.    No  medusa 
|stage  occurs  in  Hydra. 

M^^fr-^"''V'-  '"  ^  ^'''"'"  ^"'™'  ''^^^'''^^y  1^^?     in  size,  while  H 
D  n      'T"^^''^''^^^  a  dark-greeu  color  due  to  cl.loroph  ll-oontnh^ 
^g  corpuscles  imbedded   in  the  ectoderm-oelis  and   ..n.,l,.a   JTl 
Mior.  to  be  unicellular  AIg«  of  a  symbiotic  habit.     (See  p  20  ) 


f. 


IMAGE  EVALUATION 
TEST  TARGET  (MT-3) 


V 


i.r.0 


'•-.'■  ^  //„.  ^^ 


A 


4a 


1.0    !fi 


iiM 


I.I 


1.25 


1.4 


21 

|2_2 

1.6 


-(< 


Photographic 

Sdences 

Corporation 


]3  WI^ST  MAIN  STRICT 

WIB&TfR.N  Y    MSliO 

(714)  172-4503 


U.s 


84 


INVERTEBRATE  MORPHOLOGY. 


2.  Order  Narcomedusae. 
In  the  Hydrarise  the  polyp  form  occurs  without  a  medusa, 
in  the  order  Narcomedusce  the  reverse  is  the  case,  since  in  it 
the  medusa  form  is  the  only  one  present  in  a  typical  state  of 
development.  The  medusae  are  usually  somewhat  lens- 
shaped  structures  (Fig.  42),  with  a  lobed  margin,  the  velum 
(v),  instead  of  being  horizontal,  being  pendent  from  the  mar- 


(After  Bpooks). 
V  =  velum. 


Fig.  42.—Ounoctantha  octonaria  Haeck. 
TO  =  margin  of  bell.  ot  =  otocyst. 

gin  (m)  and  extending  up  in  the  intervals  between  the  lobes. 
At  the  apex  of  each  one  of  these  intervals  is  situated  a  short, 
stiff,  solid  tentacle  v/hich  is  usually  bent  backward  over  the 
exumbrellar  surface  and  is  tipped  by  a  knob  of  nematocysts. 
The  cavity  of  the  short  manubrium  leads  into  a  gastric 
chamber  which  is  prolonged  out  towards  the  margin  into  broad 
pouches  which  lie  opposite  the  tentacles  and  the  intervals  be- 
tween the  lobes,  and  around  the  margin,  following  the  edge  of 
the  lobes  and  therefore  having  a  festooned  arraugement,  runs 
n  narrow  circular  canal  which  communicates  with  each  radial 
pouch  at  the  apex  of  each  interlobular  interval.     This  struc- 
ture  is,  however,  absent  in  the  American  species  Ouiioduntha 
ocfonano,.     The  reproductive  organs  develop  in   the  auburn- 
brellar  ectoderm  covering  the  pouches  and  sometimes  extend 
on  to  the  manubrium.     Around  the  margin  of  the  lobes  are 
seated  club-shaj)ed  projecting  otocysts  (ot)  composed  of  au 
external   layer  of  ectoderm  surrounding  a  number  of  endo- 
dermal  cells,    one  or   more   of  which   contain   a   crystal   of 
carbonate  of  lime.     The  ectoderm  cells  in  the  neighborhood 
are  largely  sensory  and  provided  with  long  cilia,  their  inner 
ends  contributing  to   the  formation  of  the  marginal  nerve- 
ring. 


TYPE  OmLBNTBRA. 


as 


3.  Order  TrachymedussB. 
In  this  order  only  the  medusa  form  is  present  and  it  re- 
sembles m  many  respects  that  of  the  Nareomeuus».     The 
bol    IS  somewhat  flattened,  but  is  not  lobed  at  the  margin 
wh.le  the  velum  has  the  usual  horizontal  position  and  the' 
lo  R  slender  manubrium  projects  some  distance  outside  of  the 
sr, bumbrellar  cavity.     From  the  gastric  cavity  four,  si  "or 
e,Kht  rad.at.ng  canals  arise,  which  join  at  the  mar^-in  the  e  " 
cular  canal  and  m  the  ectoderm  of  th,  subumbreLr  surflee 
over  a  small  area  along  the  line  of  these  canals  the  reproduC 
live  cells  develop.    At  the  margin  a  number  of  sense-organs 

tZ^'ll' r  r^'*' T'"'"''  '""""'^"y  -  structure  wTth 
tluxseof  the  Narcomedu.s»  and  are  sometimes  projecting  or 
..  other  cases  more  or  less  enclosed  in  a  cavity  form  J  b; 
tl  .vowing  up  around  them  of  the  adjacent  subsUnce  of  the 
bell.  The  tentacles  vary  somewhat  in  shape  and  structure  in 
chUerent.  genera.  In  liUpalonema  thay  are  all  soM  eigU 
being  somewhat  longer  than  the  other  eight  at  whose  b^s 
are  tne  oocysts  ;  in  Mriope  (Fig.  41)  fou?,  situated  ,, p."  e 
« e  radiating  canals,  are  hollow  and  e.tensibie,  wlZ  t 
other  four  are  solid  and  bent  back  over  the  e^uu  bre  lu-  s 

4.  Order  Campanulariae  or  Leptomedusae 
uMMou  Of  labor  amoug  the  corapoueut   iudiviiluak       Tl. 

^itrde'Se-d";;  '^■«r"''"rr-'"-^-"'  ''■« « '- 

^occ.,i,whi..^^^^^^ 

1'       peiisarc,  difleriug  in  shape  tr,„„  the  hy.lrotheca 


I 


86 


INVERTEBRA TE  MORl'IIOZ  OGY. 


and  known  as  the  gonotheca  (Fig.  39,  go).  On  account  of  tlie 
presence  of  these  cups  the  polyps  of  this  ovder  are  sometimes 
termed  calyptoblastic.  In  the  typical  Campauularian  polyp 
colonies,  such  as  those  of  Aucope  or  Ohelia,  no  further  ditt'er- 
entiation  of  the  polyps  is  found,  but  in  the  family  Plumulari- 
dsB  in  the  neighborhood  of  each  of  the  small  hj'drothecae  there 
are  one  or  more  slender  extensible  polyps  lacking  mouth  and 
tentacles  Avhose  eudoderm  is  a  solid  axial  cord,  Avhile  the 
ectodermal  cells  send  off  long,  streaming,  pseudopodia-like 
processes,  these  polyps  apparently  playing  the  part  of  food- 
providers  for  the  colony. 

The  medusa3  (Fig.  43)  are  usually  very  shallow  bells,  with 
numerous  hollow  tentacles  depending  from  the  margin,  and 

resemble  the  Trachy medusae  iu 
that  the  reproductive  organs 
develop  on  the  line  of  the  ra- 
diating canals.  Of  these  there 
are  in  the  majority  of  cases 
four,  though  occasionally,  as  iu 
JEquorea,  they  may  be  very 
numerous.  Sense-organs  are 
always  present  at  the  margin  of 
the  bell  and,  as  in  the  Trachy- 
medusa3  and  Narcomedusoe,  are 
always  otocysts,  the  medusic 
belonging  to  the  vesiculate  category.  A  marked  difference 
obtains  between  the  otocysts  of  the  Leptomedusro  and  those 
of  the  two  preceding  orders  in  that  the  calcareous  crystals 
are  in  the  former  developed  in  ectoderm  cells.  Tlie  otocysts 
furthermore  primitively  occur  on  the  inner  surface  of  tlie 
velam,  where  they  are  lodged  in  a  slight  depression,  which 
may,  liowever,  deepen  so  much  that  the  otocysts  appear  to  bo 
imbedded  in  the  substance  of  the  bell. 

In  the  typical  Campanularians  free-swimming  medusre  are 
developed,  and  according  as  the  polyps  or  the  medusse  attract 
especial  attention  the  order  may  be  termed  that  of  the  Cam- 
panularim  or  that  of  the  Leptomedus«\  In  a  few  forms,  such 
as  RhegrnoUMles,  up  to  the  present  no  polyp  generation  is 
known  to  occur,  and  conversely  in  certain  genera,  such  as  ;SVr« 


Fig.  4S.—Rhegmatodes  tennis,  Ag. 


TYPE  CCELENTERA.  87 

tuhriaauiX  Ilalecium,  aud  in  the  Plumulariclfe,  e.g.  Aglaophenia 
It  would  appear  at  first  sight  that  uo  medusa  geueratiou  oc- 
curred. This,  however,  is  not  strictly  accurate,  the  appear- 
aiK-e  depeudmg  on  the  medusa-buds  iu  these  forms  never 
hecommg  free-swimming  but  remaining  in  a  more  or  less 
undeveloped  condition,  the  ova  and  spermatozoa  becoming 
mature  notwithstanding  the  imperfect  development  of  the 
niedusm.  Alternation  of  generations,  however,  exists  in  these 
tornis  just  as  much  as  in  the  typical  Oampanularians,  for  no 
inaf.ter  how  degenerate  the  buds  of  the  gonopolyps  may  be 
tliey  must  still  be  regarded  as  the  medusa  generation. 

5.  Order  Tubulariae  or  Authomedusse. 

In   this   order,  as  in  the  preceding   one,  a  well-marked 
alternation  of  polyp  and   medusa  generations  or.nirs.     The 
])()Iyps  are  united  to  form  colonies,  the  individual  hydrauths 
beujg  constructed  on   the  Tubularian  type,  i.e.  the  ^perisarc 
ceases   at  the   base  of   each  hy.lranth    so  that    there  is  no 
hy.lrotheca.     The  tentacles  show    x  greater  variety  of  form 
and  structure  than  in  the  Campanularian  forms,  and,  though 
sometimes  filiform  and  arranged  in  a  single  cycle  at  the  base 
of  the  hypostome  {ManjeUs),  are  yet  in  other  forms  scattered 
irregularly  over  the  surface  of  the  hypostome  {Clara),  or  may 
be  club-shai)ed  {Coryne),  or   in   addition    to   scattered   club- 
Kliiiped  tentacles  a  circle  of  filiform  ones  may  occur  at  the 
base  of  the  hydranth  as  in  Pennaria.     A  division  of  labor  is 
not  the  rule  as  in  the  Oampanularians,  but  nevertheless  this 
]>lienomenoii  is  in  some  cases  carried  to  a  much  greater  ex- 
tent  than  in  that  group.     In  some  forms  special  gonopolyps 
■•uo  i)resent  from  which  all  the  medusie  arise,  but  more  fre 
.;uently  any  of  the  hydrauths  may  produce  these  structures, 
llie  gonopolyps  when  t'ley  occur  are  never  enclosed  within  u 
gonotbeca.and  hence  the  term  (jumnoblastic,  frequently  applied 
to  the  polyps  of  this  order.     In  the  genus  Hydractinia  (Fig 
44)  a  complicated   division   uf   labor   occurs.      The    various 
li.xirauths  comj)osing  the  colony  arise  from  a  flat  expansion 
<oiiimon  to  all  and  formed  by  tlie  fusion  of  an  original  net- 
work  of  ccfiuosarcal  tubes,  and  on  the  surface  of  which  numer. 


88 


INVEltTEBIiATE  MOItPUOLOOY. 


ous  stout  spines  occur.  Some  of  the  hytlranths  are  typiciil 
trophopolyps  (Fig.  44,  tp)  with  filiform  teutacles  and  a  mouth, 
but  among  them  are  gonopolyps  {gp)  with  short-knobbed 
tentacles  below  which  the  medusa-buds  arise.  In  addition 
there  are  also  towards  the  periphery  of  the  colony  rauch 
longer  ■  lender  hydranths  without  a  mouth  and  like  the  gonu- 


riG  44. — Portion  of  CoiiONV  op  Hydraetinia  ccAjwato  (adapted  from  figure  by 

HiNCKSI. 


gp  —  gouopolyp.  mp  —  offensive  polyp. 


tp  =  trophopolyp. 


polyps  in  having  short-knobbed  tentacles,  but  differing  from 
them  in  their  greater  length  and  in  never  producing  medusa- 
•buds.  Finally,  in  a  European  species  of  the  genus  a  fourth 
exceedingly  long  polyp  imp),  destitute  of  both  mouth  aud 
tentacles,  but  furnished  at  its  free  end  with  numerous  nemato- 
cysts,  occurs.  These  third  and  fourth  varieties  of  polyp 
probably  are  offensive  and  defensive  in  function,  procuriug 
food  for  the  colony  aud  warding  off  some  predatory  enemios. 
The  Anthomedusffi,  as  the  medusa  forms  are  termed,  h.ivo 
much  deeper  bells  than  the  Leptomedusse,  and  differ  from 
the  latter  in  that  the  sense-organs  are  light-percipient  in  their 


TYPE  C(ELENTERA.  89 

fnnctioD,  whence  the  medusae  are  f^squentlj  termed  oceUate 

and,  secondly,  iu    that   the    re-  * 

productive  organs  develop   in 

the   wall    of    the    manubrium 

instead  of  on  the  line  of  the 

four  radiating  canals.  Ten- 
tacles as   a  rule  occur  at  the 

margin  of  the  bell,  and  it  is  at 

their  bases  that  the  e^'es  are 

formed.       Occasionally,   as   in 

Jfargelis  (Fig.  45),  tentacles 
also  arise  from  the  end  of  the 

mauabrium.  As  a  rule,  the 
sexual  generation  is  composed 
of  free-swimming  medusae,  as 
iu  Coryne,  Margelis,  and  Pen- 
naria,  but  not  infrequently  the 
medusa-buds  become  retarded 
iu    their    development,   as    iu  ^'o-  45. 


■Medusa  of  Margelis  caroli- 
nensis. 


Hydractinia,  Clava,   Tuhularia, 

aud  to  an  extreme  extent  in  Eudendrium,  and  all  intermediate 

stages  between  the  two  extremes  are  to  be  found. 


§ 

I 


6.  Order  Hydrocorallinse. 

The  Hydrocoralliuffi  are  colonial  marine  forms  represented 
by  the  Stag's-horn  Coral,  Millepora,  and  characterized  by  the 
deusely  ramified  ccenosarcal  tubes  being  enclosed  in  a  mass 
of  carbonate  of  lime  secreted  by  the  ccenosarcal  ectoderm 
aud  taking  the  place  of  the  perisarc.     From  minute  pores  on 
the  surface  of  this  calcareous  mass,  the  corallum,  the  hydrauths 
protrude  and   present  a  well-marked  polymorphism.      The 
pores  are  arranged  in  groups  consisting  of  a  central  one  sur- 
rounded  by  a  varying  number  of  smaller  ones.     From  tiie 
central  pore  protrudes  a  hydranth  with  a  circle  of  short  ten- 
tiu-los  tipped  with  knobs  containing  niimerous  nematocysts ; 
tins  IS  tiie  trophopolyp  or  gasferozoid  (Fig.  46,  g).     From  the 
smaler  surrounding  pores  more  elongated  hydranths  protrude, 
<lestitute  of  a  mouth,  and  with  short  scattered  tentacles  also 


90 


INVERTEBRATE  MORPHOLOGY. 


knobbed ;  these  are  probably  oflfeusive  polyps,  of  use  to  tlio 
colony  in  obtaining  food,  and  are  known  as  dadylozoids  (Fi^. 
46,  d).  The  cavities  in  the  corallum  in  which  the  gasterozoids 
live  are  divided  by  transverse  partitions  into  chambers  into 
the  outermost  of  which  the  hydrauth  may  be  retracted,  the 
arrangement  recalling  what  ocjurs  in  the  corallum  of  the  fossil 
Tabulate  Corals.  In  the  genus  Stylaster,  however,  which 
forms  a  rose-red   branching  corallum,  these   partitions  are 


«.-  C9 


Fig.  46.— Portion  of  Colony  of  Millepwa  (after  Mosbley). 
CO  =  comlium.  tJ  =  dactyloxoid.  fir  =  gasterozoid. 

■wanting,  a  calcareous  cone,  the  columella,  projecting  upwards 
from  the  floor  of  the  cavity. 

In  one  species  at  least  of  Millepora  a  well-marked  and  typi- 
cal  alternation  of  generations  occurs,  medusae  being  formed 
which  are  set  free  and  develop  the  reproductive  elements  iu 
the  ectoderm  of  the  manubrium.  In  the  majority  of  Uie 
members  of  the  order,  however,  the  medusa-buds  are  never 
set  free,  and  are  usually  much  degenerated,  and  indeed  in 
Millepora  alckornis  they  may  be  said  to  have  completely  dis- 
appeared, and  with  them  the  alternation  of  generations.  The 
medusa-buds  develop  on  the  walls  of  the  coenosarcal  tubes, 
and  lie  in  cavities  in  the  corallum  which  open  to  the  exterior 
by  a  pore  through  which  the  egg-embryos  escape. 


TYPE  CaSLENTERA. 


91 


7.  Order  Siphonophorae. 
The    Siphonophores    are   free-swimming    Hyclromediisan 
oolomes,  the  coiistitueut  individuals  of  which  show  a  hi.^h 
dejj;ree   of   division   of    labor.      The 
various  forms   of  individuals  which 
are  to  be  found  in  different  members 
of  the  order  are  usually  not  present 
iu  any  one  colony,  some  genera  pos- 
sessing   some    ft>rms    which    others 
lack  ;  it  will  be  convenient,  therefore, 
to  consider  an  ideal  form  iu  which  the 
various   modifications    are     present. 
Each  colony  (Fig.  47)  consists  of  an 
axis  or  stolon  on  which   the  various 
individuals   are    seated    and    which 
places  them  in  connection  with  each 
other ;  it  is  usually  long  and  slender, 
but  iu  some  cases,  as  in  Porpita,  may 
he  reduced   to   a   disk.     At  the   ex- 
:   treniity  of  the  stolon  may  be  found 
'  a  lioat  or  pneumatophore  (Fig.  47,  p\ 
a  double-walled  sac  containing  air  in 
the  interior,  and  which  is  to  be  re- 
yarded  as  a  modified  medusa  form. 
Xext  to  it  come  usually  several  medusa 
fonas  lacking  manubrium,  tentacles, 
imd  sense-organs,  and  possessing  a 
locomotor   function;    these    are   the 
swnii-bells  or  nedocalyces  (n).     At  in- 
tervals along  the  rest  of  the  stolon  ^    -^         x 
are  situated   groups    of  individuals,  Fig.  47.-DrAGKAM  of  .  Si- 

each  group   covered  over  by  one   or        " 

more  scale-like  structures  (cs),  which 
are  again  highly  modified  medusae,  and 
lu  each  group  is  to  be  found  a  fropho- 
M'//>  (;'r),  a  vase-like  polyp  form  with 
a  wide  trumpet-shaped  "mouth,  and 
iiavmg  near  its  base  a  single  tentacle 
10  which  bears  along  one  side  a  row  of  numerous  secondary 


PHONOPHORE  Colony. 
cs  =  covering  scale. 
n  =  uectociilyx. 
P  =  pneuiiiatocyst. 
r  ~  reproductive  pol^'p. 
s    =  sensory  polyp. 
ir  =  nutritive  polyp. 
t    =  tentacle. 


92 


INVERTEBRATE  MORPHOLOGY. 


branches,  each  richly  provided  with  nematocysts.  Associated 
with  this  nutritive  individual  is  usually  a  reproductive  form, 
which  in  some  cases  may  take  the  form  of  an  Anthomedusa, 
separating  from  the  colony  and  leading  a  free  life,  as  iu 
Velella,  or  may  be  medusoid,  presenting  a  medusa  form,  but 
lacking  a  mouth  and  tentacles  and  never  separating  from  the 
colony,  or  finally  a  gonopolyp  (?•)  may  occur  which  bea.'s 
numerous  much-degenerated  medusoid  buds.  In  some  forms 
there  is  still  another  form  of  individual  {s),  resembling  a  tro. 
phopolyp,  but  being  destitute  of  a  mouth  and  having  a  sim- 
ple tentacle  without  the  secondary  branches.  From  its  great 
sensibility  to  stimuli  this  is  supposed  to  be  a  sensory  polyp. 

In  some  forms,  such  as  Diphyes,  no  pneumatophore  occurs, 
but  nectocalyces  are  present ;  in  others,  as  Agalma,  both  occur 
and  the  colonies  resemble  somewhat  the  diagrammatic  form 
described  ;  while  iu  a  third  group,  including  the  Portuguese 
man-of-war  Caravdla,  the  jDueumatophore  becomes  largely 
developed  and  nectocalyces  are  wanting,  the  stolon  at  the 
same  time  being  contracted  to  a  disk  lying  on  the  lower  sur- 
face  of  the  pneumatophore.  In  Velella  and  Porpita  the  stolon 
is  reduced  to  a  disk,  but  the  pneumatophore  is  wanting. 

Alternation  of  generations  of  a  typical  form,  complicated, 
however,  by  the  polymorphism,  occurs  in  such  forms  as 
Velella,  which  possess  a  free-swimming  medusa ;  in  the  ma- 
jority,  however,  it  is  obscured,  as  in  many  Tiibularian  hy- 
droids,  by  the  greater  or  less  degeneration  of  the  medusa 
An  alternation  of  another  kind,  however,  occurs  in  some 
forms,  the  bunches  of  individuals  separating  from  the  stolon 
and  leading  for  a  time  an  independent  existence,  during  which 
their  medusoid  reproductive  individuals  become  mature. 

The  complicated  polymorphism  of  the  Siphonopliore  colonies  leads  to  a 
merging  of  the  individualities  of  the  component  individuals  in  that  of  the 
entire  colony,  a  process  which  reaches  its  highest  pitch  in  such  forms  iis 
Velella.  The  various  polyp  and  medusa  forms  of  the  colony  may  be  cnii- 
sidered  as  organ-individuals,  and  by  their  integration  an  individuality  of  a 
higher  grade — a  metamere-iudividual— is  produced. 


Development  of  the  Hijdromedusa^. — It  has  been  mentioned 
as  one  of  the  characteristic  features  of  the  Hydromedusa?  tliat 
the  reproductive  elements  arise  in  the  ectoderm.     They  reach 


TYPE  C(ELENTEIiA. 


9» 


tlieir  maturity  in  the  medusse  or  medusoid  buds  except  in  the 
Hydrarioe,  in  which  this  stage  is  entirely  wanting,  and  in  cer- 
tain Hydrocoralliuie,  in  which  it  has  disappeared,  and  may 
likewise  first  become  differentiated  in  the  medusa.     In  many 
forms,  however,  in  which  an  alternation  of  generations  occurs 
they  arise  in  the  polyp,  sometimes  at  a  point  far  distant  from 
^vhere  the  medusa-buds  will  arise,  and  reach  these  structure* 
only  after,  it  may  be,  a  rather  extensive  series  of  wanderings. 
Thus,  to  take  an  extreme  case,  in  Endendrium  the  ova  arFse 
iu  the  ectoderm  of  the  main  stem  of  the  pinuately  branching 
colon:,  a  short  distance  below  the  terminal  hydrauth  ;  as  new 
branches   are   formed   in  this   same   region   the  young   ova 
niigrate  into  them,  passing  through  the  supporting  layer  and 
Miuideriug  among  the  endoderm  cells.     Later  on*  when  the 
gouopolyps  arise  on  the  lateral  branches  the  ova  wander  into 
them,  still  in  the  endoderm,  and  finally  when  the  medusa- 
buds  develop  on  the  gonopolyps  the  ova  continue  their  eudo- 
dermic  course  into  them  and  eventually,  again  passing  throu<di 
tJie  mesoglcea,  take  up  their  final  position  in  the  meduso*id 
ectoderm.     Gradations  between  such  an  extensive  migratiou 
and  cases  in  which  none  occurs  are  to  be  found,  and  it  may  be 
stilted  as  a  general  rule  that  the  more  the  medusoid  buds 
depart  from  the  medusa  form  the  greater  is  the  migratiou 
undergone  by  the  reproductive  cells. 

As  a  rule  the  Hydromedusic  are  of  separate  sexes,  the  sepa- 
ration affecting  the  entire  colonies— or,  to  put  it  slightly  dif- 
ferently, the  medussB  are  always  unisexual,  and  a  polyp  colony 
when  it  occurs  gives  rise  to  medusae  or  medusoid  buds  all  of 
the  same  sex.  The  Hydrariae,  however,  are  exceptions  to  the 
rule,  being  hermaphroditic. 

A  blastula  results  from  the  segmentation  of  the  ovum,  and 
this  is  converted  into  either  a  sterrula  by  immigration  or  a 
(lil)lastula  (i.e.  a  hollow  two  layered  organism  without  mouth 
or  tentacles)  by  delamination  (see  p.  55).  If  a  sterruhi  be 
formed,  it  assumes  the  diblastula  condition  by  a  hollowing  out 
of  the  central  mass,  and  after  swimming  about  for  some  time 
in  this  condition,  if  a  polyp  is  to  be  formed,  it  settles  down 
upon  some  foreign  body,  a  mouth  breaks  through  and  ten- 
tacles appear,  producing  the  first  hydrauth. 


94 


INVERTEBRATE  MORPHOLOGY. 


In  some  forms,  such  as  Hydractinia,  the  free  swimming  embryo  when 
it  settles  down  becomes  converted  into  a  Hut  plate-liko  expansion  without 
mouth  or  tentacles,  from  which,  as  a  bud,  the  first  hydranth  arises. 

If,  however,  the  ovum  develops  directly  into  a  medusa,  as 
in  the  Trachymedusse  and  NarcomedusjB,  the  breaking  through 
of  the  mouth  and  the  formation  of  tentacles  takes  place 
while  the  embryo  is  still  free-swimming,  and  the  stage  so 
produced  may  resemble  closely  a  free-swimming  hydranth,  as 
in  Canoctantha,  or  may,  by  the  great  development  of  mesogkjea 
at  the  extremity  opposite  the  mouth,  assume  a  rather  globular 
form,  as  in  Liriope.  As  the  tentacles  develop  and  the  bell 
becomes  differentiated  by  the  extension  laterally,  as  it  were, 
of  the  embryo,  the  velum  arises  at  the  margin  of  the  bell. 
At  this  time  the  coelenteron  is  a  flattened  cavity  extending 
to  the  margins  of  the  bell,  but  later  it  becomes  obliterated 
along  four  lines,  and  the  obliteration  of  the  cavity  extending, 
the  radiating  and  circular  canals  and  the  gastric  cavity  alone 
persist,  a  layer  of  endoderm-cells  sometimes  joining  them 
and  representing  the  obliterated  portion  of  the  coelenterou, 
though  often  this  also  disappears. 

In  the  Anthomedusffi  and  Leptomedusse,  in  which  the  medu- 
ste  arise  by  budding  from  the  polyps,  the  buds  are  at  first 
tubular  outgrowths  of  the  body-wall  (Fig.  48,  A).  The  ecto- 
derm at  the  tip  of  the  bud  thickens,  depressing  the  central 
portioii  of  the  endoderm  (Fig.  48,  B),  and  on  the  appearance 
of  a  cavity  in  the  thickened  ectoderm,  the  subumbrellar 
cavity,  the  central  endoderm  pushes  out  into  the  cavity,  carry- 
ing with  it  the  ectoderm  covering  it  and  forming  the  manu- 
brium (Fig.  48,  C).  In  this  stage  the  bud,  though  still  lacking 
mouth  and  tentacles,  is  comparable  to  the  polyp  stage  of  the 
medusa  of  direct  development  at  least  so  far  as  the  coelen- 
leron  is  concerned,  and  by  processes  identical  with  those 
occurring  in  the  directly  developing  embryo  the  radiating  and 
circular  canals  are  formed  (Fig.  48,  E),  and  on  the  formation 
of  a  mouth  at  the  extremity  of  the  manubrium  and  the  de- 
velopment of  tentacles  the  medusa  is  perfectly  formed. 

In  many  cases,  however,  as  already  stated,  the  medusa- 
buds  never  reach  their  complete  development,  but  become 
sexually  mature  while  sfill  imperfect  in  form.     The  stage  at 


TYPE  VCELENTEHA,  95 

wJiich  development  ceases  varies  iu  different  forms;  in  Tuhu 
hirui,  for  instance,  the  medusoid  bud  resembles  a  medusa  ex 
cei^t  that  It  lacks  tentacles,  sense-organs  and  mouth,  and  is 
not   iree-swimming ;    in    (lava  not   only   does   development 
cease  at  an  earlier  stage,  but  a  certain  amount  of  degeneration 


PlO.  48.-DIAGRAM8   SHOWING  THE   DEVELOPMENT  OF  A   MeDUSABUD 

A  ontpushing  of  body-wall  of  polyp  ;  B,  tliickenino-  of  ectod.Mm  •  C  '    ' 
..on  of  subumbrellar  cavity  ;  A  tn.nsvense  ^^^^^a  .{::7:i 
.ne  uHl.cated  by  al-  E  forn.ation  of  nuHal  cauuls  ;  F.  t  ansver      ect  .n 
tlirough  E,  along  the  line  indicated  by  ah.  nausvtrse  section 

cc  =  circular  canal.  ,.,  ^  r,^,.^, 

ra  =  cavuy  of  nmnubrium.  su  =  submnbrelhu-  cavity 

»o  =  radial  canal.  .  =  velum.  ^ 

occurs,  the  rudimentary  subumbrellar  cavity  never  commu 
mcatmg  with   the   exterior   and  the  radiating  and    chX 
canals  being  entirely  obliterated  ;  and  finally  in  Ena^^Z 
the  bud  never  develops  beyond  the  earliest  stagefn  wllr  t 
13  a  simple  tubular  outgrowth  of  the  body-wall. 

The  Relationsliips  of  the  various  Orders  to  one  Another      mn.«  .1 
nvlnirioB  show  sucli  a  simple  type  of  organizationT  ifl        ,7  ^^^ 

that  they  represent  more  ol-  h  Jclosei;  ^;:  ^iTe  n  eZ7?  UT'f 
^.nisual  habitat  in  fresh  water  suggesi;  the  pos^W^'of  ^";  hr^l^' 
-.i^-.o,.o  some  degradation.     On  ti.o  supposition  that  they  rep^J^"^ 


r 

09 

i 


9(> 


INVERTEBRATE  MORPHOLOG  Y. 


primitive  Hydromc(lusr>,n  tlio  medusa  form  lias  been  regarded  as  a  socotkI- 
arily  specialized  reproductive  organ,  winch  in  the  Narcom<>dusa^  nii'l 
Trachymedusa3  has  become  so  imuortant  that  the  ancestral  polyp  kivm  js 
practically  suppressed  in  the  life-history.  On  this  view  it  must  be  sup 
posed  that  organisms  so  similar  as  the  medusa;  of  tiie  Tubulariau  and 
Campanularian  polyps  hiive  been  developed  entirely  independently  of  uim 
another,  a  view  which  carries  with  it  man;  ditiicullios,  aiid  that  tlic  medu- 
soiu  buds  represent  stages  in  their  evolution. 

It  seems  more  probable,  however,  that,  leaving  the  Hydrariit;  out  of  tiiu 
question,  in  all  the  other  groups  the  medusa  was  the  parent  forta.  Tlii,, 
i:,  borne  out  by  the  fact  that  hi  tlie  Narcomedusa;,  which,  with  their  broad 
pouch-liko  ext<;nsious  of  the  gastric  cavity,  are  the  most  primitive  of  all 

the  craspedute  medusa>,  there  is  no  lixtd 
polyp  form,  i',  lias  been  shown,  Ihav- 
e\ei,  that  the  Nareomedusee  andXraeliy- 
medusie  in  their  development  i)ass 
tl\rough  a  stage  wliich  may  be  considi'icd 
'o  represent  the  polyji  form,  and  if,  wliilu 
in  this  form,  non-sexual  reproduction 
should  have  taken  place,  the  buds  re- 
senil)llng  the  immature  form  which  gave 
rise  to  them,  a  polyp  colony  would  rcsull, 
some  of  the  buds  of  which  might  con 
tinuo  their  development  and  becoiiiu 
medusa'.  B>  this  view  the  dilliciillits 
presented  by  the  similarity  of  the  medusa 
throughout  all  the  groups  where  ihcy 
occur  are  overcome  and  the  medusoul 
bnds  are  regarded  as  imperiectiy  Uivei- 
oped  or  degenerate  medusa'.  Furili"!- 
more  this  view  is  rendered  more  than 
prol.able  by  the  development  of  Cuim- 
f<nif/itf  and  !'ie  allied  Cunina.  ll.o 
former  while  in  the  embryonic  pul}|. 
form  actually  doi><  bud  (Fig.  4!)i,  tl.i' 
buds  resembling  the  original  ei  bry(»  which  gave  rise  to  (hem,  and  all  tlio 
bud^,  the  parent  embryo  included,  later  develop  into  medusa".  In  t'liiiiim. 
liowever,  tiie  parent  embryo  whiel  gives  rise  to  buds  undeif;  )es  no  fiinliii 
developuiont,  only  the  buds  continuing  on  their  course  of  gr>wth  l(»  nutlii 
.sii'.  In  this  case  a  true  and  typical  alternation  of  g  •),  rations  occurs  aii'i 
]Kiiiits  out  a  simple  expla'iM.ion  of  the  nlternalion  which  is  found  in  \.v' 
Anlhonudiisa' and  I.epiouie  liisie.  In  these  the  jiolyp  colonies  are  tlicn- 
«i!lt.^  of  n;in-.sexual  reprodiictio'i  of  a  larval  medii.sa.  and  some  only  of  Ihi' j 
individuals  s  >  formed  continue  their  development  ie  medii.sa'. 

Tiie  relittionships  (if  the  Uydrocoialiina'  t(»  the  other  groups  av  nel  vet  I 
quite  demonstrated.     It  woidd  seem,  however,  from  tiie  uie(hisa-bud  wiiiilij 


Fio.    49.— Brpnrxo   Laiiv\    of 

Cnnoct.inti.il    octoiuiv'a     caftt-r 
McOrkadv.  from  Hudoks). 
a  —  egg  larva. 
ub  =  buddeil  laivte. 


TYPE  CCELENTEUA. 


97 


occurs  in  one  species  of  Millepora  having  its  reproductive  organs  in  tlie 
walls  of  tiio  manubrium  that  the  amnities  of  the  group  are  with  the  Antho- 
incdiistB,  and  that  an  exceptional  amount  of  degeneration  of  the  medusa 
liad  occurred  in  correspondence  with  tiie  development  of  the  calcareous 
conillura. 

The  Siphonophores  are  evidently  allied  to  the  Anthomedusa?,  judging 
from  Mie  characters  of  their  medu3ie.  The  colony,  however,  contains  both 
iiHMlii?a  and  polyp  individuals,  the  former  not  being  in  all  cases  reproduc- 
tive as  in  the  Anthonieduste.  The  emin-yology  of  those  members  of  the 
or(i(>r  which  have  been  studie<l  in  this  particular  iiidicates  that  they  too  must 
l)c  nrarded  as  produced  by  budding  in  e..d)ryoiiic  stages,  some  of  the  buds 
developing  to  medusie,  others  remaining  in  tlie  polyp  stage.  A  further 
differentiation  of  the  medus<-B  took  place  by  which  ihe  pneum.itophore, 
iieet.. calyces,  and  covering  scales  iiavo  been  specialized  from  meduste  ori-i- 
ually  reproductive,  the  i.neumatopliore  prol)ably  reprefsentii.g  the  parnit 
individual  of  the  colony.  It  is  interesting  to  note  in  this  connection  that 
111  souk;  forms  the  reproductive  medus*  after  having  expelled  their  ova  or 
spenuiitozoa  become  converted  into  nectocalyces. 

II.  Class  Scypkomedusje. 

In  the  Scyphomedusro  the  medusa  form  is  preemiueiit,  the 
poly])  form  beiug  placed  in  the  backgrouud  and  occurring 
only  ;is  a  larval  stage,  though  iu  some  forms  it  assumes 
somewhat  greater  im])ortaiice  on  account  of  the  power  it  may 
possess  of  re])roduction  by  transverse  division. 

The  medusai  are  usually  free-swimming,  though  a  few  of 
the  more  lowl;  organized  forms  are  attached  througliout  their 
lives  by  a  prolongation  of  the  exumbrellar  surface  (Fig.  52), 
iV-rniing  a  connecting  link  between  the  free-swimming  forms 
and  the  polyj).  As  a  rule  they  reach  a  much  greater  size 
tliuii  do  the  Hydromediisas  from  which  tliey  are  further  dis- 
tinguished by  {(()  tlie  absence  of  u  velum,  \h)  by  the  sense- 
-T-.ns  when  present  being  modified  tentacles,  and  (c)  l,v  the 
it'l'iO'liK'tivo  cells  always  arising  in  the  endodorm.  On  ac- 
cnnt  of  fhe  iirst  of  these  characters  the  Scyphonieilusa' are 
sniiiotimes  termed  the  AcvaN'mda. 

They  are  all  more  or  less  bcdl-shaped,  a  number  of  ten- 
tildes  usually  haijging  from  the  margin  of  the  bell  (Fig.  53). 
Tlu'se,  howev(u-,  are  frequently  secondarily  develoj.ed,  there 
i-ing  in  the  simjiler  forms  eight  i)rimary  tentacles  which  may 
l"isist  as  tentacles,  or  four  or  all  of  tliem  may  be  converted 


§ 

r 


S8 


rnVKUTEBHATE  MOliPIIOLOG Y. 


into  seu^-a-orgaus  (Fig.  50,  s)  situated  uear  the  margin  of  tiio 
bell  anil  more  or  less  enclosed  in  special  chambers  by  tlio 
growth  around  them  of  folds  of  the  bell  substajico  (/).  From 
the  centre  of  the  subumbrella  there  hangs  the  manubrium 
(m),  the  extremity  of  which  is  fre(j[U(?ntly  prolonged  into  four 
elongated  mouth-k)bes,  and  above  it  communicates  with  tlio 
gastric  cavity,  f/,  which  in  simple  forms  extends  to  tliti 
nnirgiu  of  the  boll,  being  obliterated  only  at  four  interradial 
points  or  lines.  The  four  broad  radial  pouches  thus  })roduc('(| 
correspond  with  the  radiating  canals  of  the  cras[)edote  medu- 
sa*, and  the  line  of  fusion  being  imperfect  at  the  margin  of  tlio 


Fid.  50.— DrAOHAM   OK   SCYI'IIOMKOITSA. 

j7  =  iiasfric  cavity.  r  =  rt'pn.dtutivo  oisans. 

I  =  l()hi>  oovoring  the  st'iLso-orgiiii.  «  =  sfiisn-orgaii. 

m  -  inoiiili.  ig  =  suligciiilal  cavity. 

vif  =  lucseiiteiial  filaments.  t  =  toiitacle. 

bell  a  communication  between  adjacent  ])()U('hos  is  present 
comparable  to  the  craspedote  circular  canal.  This  condition 
is,  however,  oidy  retained  in  the  simpler  forms  ;  in  the  higlit  r 
Hcyphomedusu*  the  lines  or  points  of  oblitenition  nuiy  1h' 
omitted,  and  by  secondary  oblit(M-ations  taking  ])]ace  ov<i 
various  areas  of  the  c(elenteron,  ami  by  its  irregular  extension 
towards  the  rim  of  the  bell  as  this  grows  in  diameter,  a  com- 
plicated branching  arningement  of  the  peripheral  p()rtit)n  of 
the  C(rlenteron  is  jtroduced,  in  which,  however,  the  origiiuil 
4-radial  arrangement  is  ns  u  rule  distinctly  indicated.  Aloni,' 
the  interrudial  axes  tin  re  are  four  deoj)  depressions  of  tin' 
subumbrellar  surface,  the  finnicls  or  ,snl>((f')iifiil  rhaniherfi  (V\\: 
60,  s(f),  above  which  lie  the  hor.seshoe-shaped  reprodm-tiw 
organs,  r,  devsloppd  in  the  c«e|ej!toric  endixlerm,  nrm  lim!)  -M 
«ach  horseshoe  lying  in  each  of  the  adjacent  radial  pouches. 


TYPE  COiJLENTEUA.  9^ 

Fi..;tlly,  ill  the  line  of  each  interradius  there  project  into  the 
n.lontonc  cavity  a  number  of  coarse  thread-like  tilaments. 
i^^  mesenterua  JiUuuaU.  ^,./),  which  are  unrepresented  in  the 
llydromedusat. 

Such  is  the  |,.eneral  structure  of  the  Scyphon>edus,x) ;  the. 
n...d.hcat,on.s  will  be  better  described  in  connection  with  the 
various  ord<n-s  into  which  the  class  may  be  divided.     In  histo 
l.-u-al  structure  the  resemblance  to  the  Hydromedusu.  is  so' 
K.vat  as  to  do  away  with  the  necessity  of  a  detailed  account. 
.xrcpt  as  re^anls  the  sense-organs.     As  already  stated,  these 
w  on  present  are  modilied  tentacles  and  partake  of  the  char- 
.•.ri,>rs  <,f  both   eyes  and   otocysts.      The>   are   usually  short 
l.-Kor-hke  stalks,   lym^r  i^   a  notch   of  the   rim   of  the    bel 
a.ul  covered  over  by  folds  (corerhu^  ploU.,  Fi.  51,  cp)  ansin« 
trn.u  the  .djucent  substance  of  the  bell  on  either  side  of    ha 


cp- 


Fu..  51.-Mai.«,nat,  SKNSK-oaoAN  „F  Rhopalonema(nn.v  lunrmo) 
cc  =  cHcnlcri,-  .-nvily.  ^n  .  eudoduu.. 

cp  =  (ovcrii.u  pliilo.  ^  ^ 

ot  =  otocyst. 

•iH-ho  ami  frequently  uniting  so  that  the  st.lks  lie  in  pouch- 
'■'-  <'.''v.t,es.  The  ectoderm  of  the  lln^er-like  stalks  contains 
•"•n.erouH  sensory  and  ^.tn^dion  cells,  and  at  <.ne  or  more 
■■.•K.O..S  pigment-cells  are  associate.l  with  these  to  form  the 
;'.v;;("  .  whu-h  nnt^.  be  further  perfected  by  the  a.ldition  of  a 

>'  u-nhu.  lens  The  stalks  are  hollo, v.  containing  a  prolon,u- 
o  h.  ,  len  .r.c  n.vity  (cc)  lined  by  cn.lodern,  and  at  Uie 
tip  nf  the  sta  k  the  en.loderm-cells  are  lilled  with  crvstals  of 
oaibonato  of  l.me,  the  whole  mass  of  crystals  formin^/a  rath... 
i--^.  ulnc^vst  (o/,.  The  covering  plates,  furthermore,  above  tlie 
•SH.sory  stalks  are  usually  grooved,  tin-   bottom  of  the  groove 


(*'• 


100 


INVERTEBIiATE  MORPHOLOGY. 


being  lined  by  sensory  cells  to  which  an  olfactory  function  is 
attributed.  The  marginal  sense-organs  of  the  ScyphomedusiB 
are  thus  much  more  complicated  in  structure  and  in  additiou 
have  a  different  mode  of  origin  than  those  of  the  Hydrome- 
dusse. 

1.  Order  Stauromedusse. 

In  this  order  some  of  the  forms  are  fixed  throughout  their 
adult  life,  e.g.  Zucernaria  (Fig.  52);  while  others  are  free- 
swimming  when  mature,  as  Tessera.  The  deep  bell  has  at 
the  margin  eight  tentacles  — the  primary  tentacles,  none  of 
which  become  modified  into  sense-organs,  these  structures 
being  wanting  in  the  group.     In  some  species  of  Zucernaria 


Fig.  52— JJalidystua  auricula  divided  i-ongitudinally  (after  H.  Jamks-Cl^uk 
/  =  funnel.  inf  =  mesenterial  liliiuieuts. 


po  =  lepiodiictivo  oijfans. 
in  =  iutenailial  adhesion. 


rp  =  radial  pouch. 
t  =  uioditied  priuiury  tentacle. 


these  primary  tentacles  {t)  are  somewhat  alteretl,  and  in  all 
the  margin  of  the  bell  is  produced  into  eight  knob-tipjuHl 
lobes,  to  each  of  which  a  bunch  of  secondary  tentacles 
may  be  attached.  The  CtX'lonturoii  ei'teads  out  io  the  niar^nu 
of  the  bell,  and  is  interrupted  along  tlie  interradii  by  a  poiut 


TYPE  CCELENTERA. 


101 


{L  aa)o.  I  ue  Z^,-n«na)  of  adhesion.  The  depression, 
ol  the  subumbrellar  surface,  the  funnels  (/),  are  verj  deep  in 
Lucermxria,  extending  almost  to  the  summit  of  the  bell. 

2.  Order  Peromedusae, 

In  this  order  the  adult  medusu3  are  always  free-swimmin^. 
and  are  characterized  by  the  bell  being  pointed  in  shape  and 
about  Its  middle  marked  with  a  distinct  constriction  The 
CO. lenteron  IS  obliterated  at  only  four  points,  as  in  Tessera, 
Hud  they  difler  from  the  Stauromedusje 
bj  possessing  four  sense-organs,  the 
four  interradial  tentacles  of  the  i^rimury 
.series  of  eight  becoming  modified  to 
form  these  structures,  while  the  radial 
€ue;s  retain  their  original  character. 

3.  Order  Cubomedusse. 

This  order,  of  which  CJiaryhdea  (Fig. 
o3)  is  a  typical  example,  is  characterized 
by  the  bell  being  of  a  cubical  shape. 
The  interradial  obliterations  of  the 
Cd'leuteron  are  linear,  and,  as  in  the  pre- 
ceding order,  four  of  the  primary  teu- 
taclos,  these  being  the  only  ones  which 
tlevelop,    are    modified    to    form   seuse- 

or^'uns.      In   this    order,  however,  it    i^Y^o.^^.-CkaryMeamar^ 
tlie  lour  radial  tentacles  which  form  tiie     •■"/;»•'«//.' u,f.erci^u8,. 
seuso-organs  {so),  the  Tour  interradial  per-       "^  =  scuse-orguu. 
sistiiig  as  tentacles  {t).  '  =  tfiiiacle. 

4.  Order  DiscomedusBB. 

I.,  this  order,  which  includes  the  maiority  of  the  known 
S(Tphomedusa^  all  the  eight  priinary  ten'..,  '.s  are  converted 
int..  sense-organs,  a  number  of  secondary  tentacles  usuallv 
<levoloping  at  the  margin  (Fig.  54).  The  prinmry  intenadial 
-umcious  of  the  cu^ienteron  do  not  develop,  but  on  the 
"HT  hand   secondary  obliterations   frequently  make   their 


I 
5 


102 


INVERTEBRATE  MORPHOLOQT. 


»: 


appearance,  wliicli,  combined  with  irregularities  of  growth  of 
tbe  coelenterou,  give  its  peripheral  portions  an  irregular  out- 
line {Cyanea),  or  convert  them  into  a  series  of  anastomosing 
canals,  e.g.  Aarelia.  The  margin  of  the  bell  is  usually  more 
or  less  lobed,  eight  of  these  lobes  being  especially  distinct 
and  carrying  the  sense-organs,  the  intervals  between  them 
being  usually  occupied  by  the  secondary  tentacles  when  these 
are  present.  The  depressions  of  the  subumbrellar  surface  are 
no  louger  deep  funnels,  but  form  rather  shallow  subgenital 


Fig.  54. — Pdagla  cynnella  (after  Aqassiz). 

chambers  with  thin  roofs,  into  the  cavity  of  which  the  rejjio- 
ductive  organs  bulge  out. 

lu  many  forms  the  margius  of  the  mouth  are  prolou<.^o(l 
into  long  fringed  lobes,  and  in  one  family,  the  Rhizostomida 
(e.g.  Stomohphiis),  the  nmrgius  of  these  lobes  may  fuso  to- 
gether, leaving,  however,  a  large  number  of  minute  oneniiii.'" 
along  the  line  of  fusion.     These  lead  into  canals  traversiug 


the  substan 
central  can  a 
mouth. 

Developm 

the  ovum  le 

come  solid  1 

may  abbrevi 

Tlie  gastrula 

iuhilt  conditi 

swimming  ha 

life-liistory  is 

tluste,  the  em 

sessile  existei 

form  (Fig.  5£ 

rially  from   tl 

body-wall    th 

ridges  (mesen 

the  mouth  to 

give  rise  to  th 

the  second  ph 

each  one  of  t 

Scyphostoma, 

the  medusoB. 

The   Scypl] 

swimming  met] 

series  of  trans 

saucer-like  strn 

notched  prolou 

phostoma  and  i 

into  the  adult 

eight  lobes,  wh 

lievelopment  of 

A  typical  altern 

There  can  be  lit 
•sfssilo  organism  wi 
lines  of  descent  aroi 
't'ntades  and  term 

.M  'iiu  i7iscorae 

I  'It'velopment.    So  f 


TYPE  C(ELEr'^ERA. 


103 


the  substance  of  the  lobes,  and  uniting  finally  in  a  lar.^r 
cea^^^^^^  canal  at  the  upper  extremity  of  /hieh  lie's  Ihe  or^n  J 

Development  of  the  ScyphomeduscB.~The  segmentation  of 
the  ovum  leads  as  usual  to  a  blastula  form  whTch  tt  ,./ 
co.e  sohd  by  immigration  and  subsequentl/holl^^^^^^^^^ 
may  abbreviate    these    processp^   h^  a\      •     ,   .^  ^^^'  or 

a>h,U  couditiou  iPA,gia),  without  ever  "lum^S  t^ 

My.mM    there    i.roiect    in^i  '  H  ?        '     '"'•  ''■°'"  *''« 

mli  (.ueseutede  „h  e  L k  'Lr  f  "■""  ■  ^"■   "'"^"^ 

ll»  mouth  to  the  posterior  e„,rVM  f  "''e''l>«l'oo'l  of 

«ive  rise  to  the  .L^  ^uVu^"''""'-  ^""  ""^^ 

«.p.»a,«.>proa„eeS^^^^ 

The   Scyphostoma   may  develon  dirn^fi,,    •  .     .,       . 
«»--.iuK  ,„e.lu..,  but  in 'a  uuIZofS  it'  1    '^      "■ 
series  o(  transverse  divisions  (Fig   55  /ft  T,!t '    "'"''"8°'*''  » 

p..osto  ja  j:rc„urj;.~  rs  '1' )  rr  '"^- 

■«lo  the  adult  Biscomedusau  by  theiutrv,')  .""  "P""*-' 
«Kl.t  lobes,  whieh  earr,  the  J.^^^.^'t^T  h" 
'levelopraeiit  of  tentacles,  and  by  the  irrowH,  f  "  , '  ^  "'° 
.U,pica>  alternation  of  KeneraLt^TZ^tS^atr- 

;«-  Of  d„so„„t  arose.  b„.„  ..uSt      ,    „  w7:f '    ^'■™  ""»  '»- 

.'-  "'^tJ  i^iscoraeuusjt!  resiiltinr-  in  iha.  „,.i    •     ..     "'fcauas;  icspec- 


104 


IN VEIi TEDHA  TE  MOIWIIOLOG  Y. 


Epliyra  seems  to  represent  an  ancestral  stage,  since  some  matnre  medusae 
resemble  this  stage  very  closely  and  it  occurs  in  the  life-history  of  all,  ami 
earlier  than  this  is  the  Scyphostonia  representing  tlie  Lnccntarfa  stage  of 
evolution.      The  iScyphobtoma  has  superficial   resemblance  to  a  hydroid 


Fio.  55.—^,  Scyphostom  of  Aurclia  ;  B,  Strohila  of  Aurelin  ;  C,  Ephyra  of 

Pekujia  (aU  after  Aqasbiz). 

polyp,  which  resemblance  is  almost  an  identity  in  the  earlier  stages  of  the 
81'yphostoma  before  the  development  of  the  mesenteries  and  funnels.  This 
suggests  a  relationsliip  of  the  Scyphomedusae  to  the  Hydromedusa;  only 
through  the  polyp,  the  separation  of  the  two  classes  having  occurred  be- 
fore the  appearance  of  the  medusa?  on  the  scene. 


III.  Class  Anthozoa. 

The  Anthozoa  never  assume  the  medusa  form,  but  are  ses- 
-sile,  usually  colony-produciug  polyps  of  the  Scyphostoina 
type.  Typically  they  are  cylindrical  structures  (Fig.  56)  at- 
tached at  one  extremity,  the  base,  and  bearing  at  the  other 
extremity  the  mouth  in  the  centre  of  a  flat  surface,  the  disH, 
around  the  margins  of  which  are  a  number  of  hollow  tenta- 
cles. The  coelenterou  is  imperfectly  divided  into  a  number 
of  chambers  by  !ongitudi?!nl  j^-urtitiring  arising  from  the  b^xlV' 
wall,  the  mesenteries  (Fig.  o7,  me),  the  various  iutermesenterial 


TYPE  Caer.ENTEllA.  JQ5 

cliauibers  commniiicatiDs  fredv  ivitl,  „  ,     .    i 

.....nth  does  ..ot  opeu  dhecti!   n.      ,  ,"■"'  'P'"'^-     ^Le 

1..V.I.OJ.1  poi„«.  L  il:  tr;,  el,::'?';™' "» -  «- 

by  ectoderm  aud  cou^muuica  uTf,:  ,  """«"'"  <">>  ''"«' 
o-leuteric  space.  CerZ"  .L  ^  ^'  !  "  *'"'  ""^  ''''""■^' 
p..rtK."»  «e  attachedtTreUodZr  "r  '"."'"'■  '■"'^"'• 
'■"l-".n,  but  below  it.  lower  ™d  an         J  ""'  "'  ""*  '''"""'• 

-^  ^-  ed«e  tbere  r„., ,.  ™::i;:L'':r re-t^it:? 


Fig.  56.  -  Metrfdinm   margina- 
tum, Le8. 


Fig.   57.-DiAGRAjfMATic  Traks- 

VEHSE  SECT10i<  THKOUCiU  AVmrd- 
««  IN  ItEoxoN  OP  StoMATOD^UM. 

'"ie  =  iiieseulery. 
rm  =  rcliuclor  iiiubcle. 
«'    =  sipbonoglypiie. 
St    =  sloiiiuioiiteiiiji. 
I-IV  =  uasenteiies  iu  iLc  order  of 
tlitir  developuifcui 

svslen,  of  coils  aud  iwkT  T.  i,^  "  "  •'"'"V^'^'^i'^d 

«U:eut  sr  erirrrlTidrd"  T  ■"^-■''-.V»  "buucb  of  Hue 

l^ei.«  l»otr„deVfZ'  bet  urh":";!?'^  T"  """"^'■'  "^ 
l'«lywall.     Tbe  upper  part  rH»^°l  x"*'''  P"''""  '"  "'« 

fe'«'t  structure    l,T'  '  "'efilameut  is  usually  of  dif- 

h'i«tea    e  Is  "L'e  ful""  T'T'^  "  ■"""•  "'  «'™8«'«I 

l«-  fl»ij.  iu  ibe  cr,eu.:,t  " '°  "'"'""^ "  "■•'•''■■"^«™  "f 

'"'  -P'oductive  cells  develop  iu  the  .      ,deru,  of  tba 


106 


INVERTEBRA TE  MOBPHOLOQ  T. 


mesenteries,  whence  they  are  shed  into  the  intermesenterial 
chamber  and  make  their  exit  by  the  mouth.  The  nervous 
system  is  well  developed  especially  in  the  ectoderm  of  the 
disk  and  tentacles,  though  it  also  occurs  in  the  endoderm. 
It  possesses  the  general  character  of  the  Coelenterate  nervous 
tissue  consisting  of  sensory  cells,  nerve-fibres,  and  gangliou- 
cells.  The  muscular  system  is  very  well  developed  both  iu 
the  ectoderm  and  endoderm,  the  muscle-fibres  being  generally 
longitudinal  in  the  former  layer,  and  in  the  latter  circular  ia 
their  direction.  At  certain  regions  of  the  body  the  muscle- 
fibres  are  especially  abundantly  developed,  the  mesogloea 
being  thrown  into  complicated  folds  for  their  support,  so  that 
it  is  possible  to  distinguish  certain  definite  muscles.  One  of 
these  is  developed  upon  one  face  of  each  mesentery,  and,  its 
fibres  being  directed  longitudinally,  it  forms  a  strong  retractor 
(Fig.  57,  rm)  for  the  disk  and  tentacles ;  a  second  is  developed 
in  the  endoderm  of  the  body-wall  a  short  distance  below  its 
junction  with  the  disk,  and  its  fibres  may,  by  the  growth  of 
the  mesoglcea  around  them,  become  imbedded  in  that  layer ; 
it  forms  a  more  or  less  powerful  sphirwte?',  serving  to  cover  iu 
the  disk  and  tentacles  when  these  have  been  retracted  by  the 
mesenterial  retractors. 

The  Anthozoa  are  constructed  upon  a  radial  symmetry, 
as  are  the  other  Coelentera,  this  symmetry  appearing  in  the 
arrangement  of  the  mesenteries  and  tentacles  and  in  the  cylin- 
drical form  of  tho  body.  Nevertheless  it  is  always  possible 
to  divide  the  Anthozoan  by  a  single  plane  into  two  simihar 
halves,  that  is,  a  bilateral  symmetry  is  also  present  which  is 
produced  by  the  arrangement  of  the  retractor  muscles  on  only 
one  face  of  each  mesentery  and  by  the  flattening  of  the  sto- 
matodffium.  This  latter  feature  is  furthermore  usually  made 
more  pronounced  by  the  occurrence,  at  one  or  both  ends  of 
the  longer  transverse  axis  of  the  stomatodseum,  of  a  distinct 
groove  lined  by  high  columnar  cells  with  long  cilia,  these 
grooves  forming  the  siphonoglyphes  (Fig.  57,  si),  and  by  the 
mesenteries  which  are  attached  to  the  stomatodteum  in  the 
neighborhood  of  the  siphonoglyphes  usually  having  their 
retractor  muscles  on  different  faces  from  those  on  whicli  they 
occur  iu  the  other  mesenteries. 


Fig.  58.— DiAGii. 


TTPB  CWLENTMBA.  jqj 

Frequeatlj  the  ectoderm  of  the  autl.o;,oau  polyns  secr.t„ 
».  sle  etal  substauce  wl.ich  may  either  be  carbo.ateof    me  o 
el,e  au  orgauic   substauce  of  a  horuy  eo.dstency       iTib' 
corals  the  secrohou  takes  the  fonu  of  earbo.ate  rf  lime    '  d 
io.n,s  a  cup  (F.g.  58.  ap)  in  ,vhich  the  polyp  is  sealenj;:' 


Fro.  Sa-DiAGUAM  OP  THE  Stbuctcke  ok  a  Coiul  (after  voK  KOCH,  from  u.a, 
«;?  =  exotlieca.  ;,„ 

fP  =  basal  plau,.  t  I  ^"J""^- 

Calcareous  skeleton,  wLi.e;  ectoderm,  sbaded,  mcsog,„„,  black;  e.doderm 

dotted.  ' 

(sepfa  H  over  which  the  soft  tissues  of  the  uuimal  are 
Moulded,  projecting  np  fro„>  the  botton,  of  the  c,  p  Tl  e 
septa  may  be  united  by  delicate  tauKential  bars,  sJ,ptic2 
a«  from  the  botton.  of  the  cup  a  somewhat  cyl  nS  o S: 
*  may  project,  other  upright  rods.  the^„?t,  inter  en  mb 
t»eeu  the  free  edges  of  the  septa  and  the  columella     The 

„  ;  '  /  <=f  l'^"«o'>«  enp  and  n,ay  produce  ridges,  co.I.e 
0"  ts  outer  surface  corresponding  in  position  with  Vhe  sen  a 
ami  „,as,„„ch  as  the  cup  is  continually  increasing  in    eptl  lo 

V^Z    he'T  ■'■"  '""■""''  "'^  >'"'-n'  -'-voccupis  theC 
1.0  ton.    he  lower  part  m, ay  from  ti„,e  to  time  be  separated 
oa  liy  a  transverse  partition  or  dissepiment 

Ii.  other  forms,  such  as  the  Alcyouarians,  however   the 
skeleton  .s  secreted  only  by  the  basal  ectoderm  and  thTcolon; 


108 


iiV  VKRTEliHA TE  MOlWUOWa  Y. 


becomes  moukletl  over  it  (Fig.  69),  so  that  it  forms  a  ceutml 
lioruy  or  more  or  less  calcitied  axial  support,  aud  iu  udilition 

the  mesoglcjoal  cells  secrete  scatten d 
particles  of  carbonate  of  lime,  liaviiig  a 
more  or  less  detiuite  form  for  each  spe- 
cies, but  uot  uuitiug  together  to  form  a 
firm  skeleton. 

The  development  of  the  Autho^ioa  is 
always     direct,     aud     the     diploblastic 
Fig.  59.  — DiAGitAM  op  condition    is     produced     by     delamina- 
Young  Gohoonian  (af-  tion  of  the  cells  of   the  blastula.     Muuv 

ter  VON  Kocu).  i     li.       r  ii 

adult  lorms  possess  the  power  oi 
division,  either  transverse  or  longitudinal,  the  latter  giving 
rise  to  complex  colonies  in  many  cases.  In  other  forms  the 
primary  polyp  may  develop  a  stolon  from  which  other  imli- 
viduals  may  bud,  producing  a  diffuse  colony,  or  the  intervals 
between  the  individuals  may  be  filled  up  by  a  growth  of 
mesogloea  traversed  by  a  network  of  canals,  forming  a  tissue, 
the  coenenchyme  (Fig.  60),  in  which  the  various  individuals  are 
imbedded. 

The  class  Anthozoa  may  be  divided  into  a  number  of 
orders,  whose  existence  depends  mainly  on  the  arrangement 
of  the  mesenteries. 


1.  Order  Alcyonarise. 

The  majority  of  the  Alcyonarians  produce  colonies  by  bud- 
ding. In  some  the  individuals  are  scattered  on  stolons,  iu 
others  imbedded  in  a  coenenchyme  {Alcijonium,  Fig.  60),  or  in 
others  united  to  form  flesh}'  colonies  of  a  feather  or  renifi^rii' 
shape  {Renilla),  the  whole  being  imbedded  in  the  sand  by  ,. 
fleshy  stalk.  In  some  of  the  groups  a  horny  or  calcareous 
skeleton  is  present  in  addition  to  the  calcareous  spicules  im- 
bedded iu  the  mesoglcea  and  may  form  a  central  axis  enclosed 
by  the  coenenchyme  (Fig.  59)  and  of  a  horny  consistency,  as  in 
Gorgonia  ari(»  Lep^ogorgia,  or  more  or  less  calcareous,  as  in 
Isis  aud  Cv..''ta?\(:>?,  tlie  skeleton  of  the  latter  constituting  the 
red  coral  of  commerce.  In  the  Organ-pipe  Coral,  Tuhipam, 
each  individual  lives  in  a  calcareous  tube,  the  various  tulies 


TYPE  CCRLENTBRA. 


109 


.oiug  united  by  transverse  plates,  and  in  Helio^nyra  the  skeleton 
l^ocomes  very  massive,  resemblir  -^  tlmt  c.f  the  ..rdinarv  corals 
even  to  the  occurrence  of  septa  projecting  into  the  interior  of 
tlie  cups  which  contain  the  individual  polyps 

xNotvvithstanding  these  manifold  variations  of  the  skeleton 
H.ul  of  the  colony  form,  the  individual  polyps  present  through- 
out  a  great  similarity  of  structure.  They  possess  only  eight 
pinnate  tentacles  and  eight  mesenteries  whose  retractor  mus 
d.s  are  arranged  in  the  manner  shown  in  the  annexed  dia- 
grammatic cross-section  of  a  polyp  (Fig.  61).     lu  li^^Ma  and 


rm- 


Pia  6O.-D1AGKAM  <,K  Y<,t;NG     F,o.61.-DuorammaticTkan8vehbe 
v.?N  K^L**^  ^^cyo»*MWJ  (after        Section  of  an  Alcyonauian. 

^"«  =  retractor  muscle. 
»i  =  siphouoglyphe. 
I-IV  =  mesenteries. 

allied  forms,  such  as  Pmnatula,  a  slight  polymorphism  occurs 
certain  polyps  possessing  no  tentacles  and  functioning  as 
n^/./m^  «oozc^.  through  which  currents  of  water  pass  into  the 
cclenteric  cavities  of  the  colony  through  which  they  circulate. 

2.  Order  Edwardsise. 

The  Edwardsitie  never  produce  nnlr.r.iVc         j    i, 

a  skeleton,  tl.ongh  frequently  1  ee"^Wo7«,:'^7'^"^'' 

c-nsted  by  foreign  particles.    Thev  I  ve  ",„'.'  i    ,    T/.™- 

M'l,  the  base  beinf>  rouofled  ^rl Zt  T     '   ^^^^^"'^  » 

eight  (sometimes  si^teeTor  tbi  tv r\    •  'T''  """^  ""^^^'^ 
oi.Tl,tm„-,.  I     •       '  tliirtr-twol  simple  tentaole=  „„j 

o.„ht  mcontenes,  a,fleri«g  from  those  of  the  AIoyonaria.s  i^ 


110 


INVERTEBRATE  MORPHOLOGY. 


the  ari>.ugement  of  tho  retractor  muscles  as  shown  in  Figuro 
67. 


3.  Order  Ceriantheae. 

The  Ceriauthoro  are,  like  the  Edwardsi.T,  solitary  forms 
destitute  ci  v.  skeletou,  uiul  live  imbedded  iu  saiu!  or  mud. 
Tho  basal  region  is  roundod  and  not  adhesive,  having  at  the 
centn?  a  pore  which  conimuniea  3s  with  tho  eoeleuteron.  Jji 
Ceriivnthun  a  tibrous  investment  surrounds  the  body  ay  a  tabc, 
secreted  by  the  ectoderm,  this  layer  of  the  body  being  further 
characterized  by  an  enormous  development  of  muscle-tibres 
arranged  longitudinaiij  and  supported  upou  slender  processes 
of  the  mesoglwa  of  the  body- wall.  The  tentacles  are  simple 
and  very  numerous,  being  arranged  in  two  setS;  one  surround- 
ing th{»  margin  of  the  funnel- 
shaped  disk  and  the  other  im- 
mediately surrounding  the 
mouth.  The  mesenteries  are 
also  very  numerous  and  are 
distinguished  by  the  absence  iu 
the  adult  of  '-e tractor  muscles, 
the  ectodermal  muscles  playing 
the  part  of  the  retractors,  and 
the  tdiaracteristic  Antln)Z()iin 
sphincter  is  also  absent.  The 
arrangement  of  the  meyanteries 
(Fig.  02)  is  peculiar  to  the 
group,  new  ones  continuing  to 
form  during  the  entire  life  of 
the  animal  and  making  their 
appearance   one   on  each   side 


VEU^K  Skition  ok  a  YotiNO  Ceri- 
anthus  (according  to  Caiu-ohkn). 
Hi  =  slphonofflyplic. 
I-IV  =  tlie  Edwftrdsian  inosciiteries. 
1-4  =  si'coiidiiry  incscntcrios. 


of  the  sagittal  plane  between 
the  two  which  immediately  preceded  them.  The  older  mes- 
ontories  are  thus  cowdod  to  one  surface  of  the  body,  tlie 
dors.d  surface,  at  which  the  single  sii)honogiy})he  {si)  occurs 
in  the  sfomatodaMim,  and  the  four  on  either  side  of  flie 
mid-dorsal  line  (/-/F'>  are  the  homologues  of  the  ei^lit 
mosonteries  of  the  Edwardsiir,  tiie  rest  being  secondary 
structures  not  represented  in  that  group. 


TYPE  V(ELENTERA. 


Ill 


4.  Order  Aniipathariae. 

The  members  of  this  order  are  jill  colonial  aiul  secrete  a 
hnuichiiig  axial  skeletou  of  u  black  horuy  material.  The 
lH.lji)s  possess  usually  but  six  simple  tentacles,  and  as  a  rule 
only  six  mesenteries  are  ])resent,  of  which  only  the  two  lyin^ 
ill  the  transverse  axis  bear  reproductive  organs  and  mesen'^ 
t.^rial  filaments  ;  in  some  forms  four  or  six  additional  imper- 
t(!ctly-developed  mesenteries  are  present,  but  six  seems  to  be 
the  number  tyjjical  for  the  group. 

5.  Order  BrotactinisB. 

This  order  includes  a  group  of  forms,  all  sim^  le  and  with 

smiple  tentacles,  but  showing  ccmsiderable  vari  tion  in   the 

iminber  of  the  tentacles.     They  all 

agree  in  this  particular,  however, 

that  there  are  twelve  mesenteries 

arranged  in  pairs  (Fig.  03,  I-VI\ 

the  two   pairs  attached  to  the  si- 

l)honoglyi)he  region  of  the  stoma- 

todioum     having     their    retractor 

muscles  on  the  faces  turned  away 
I'lom  each  (jther,  while  in  the  other 
four   pairs    they   are    on   adjacent 
laces.     The  two   former  pairs   are 
termed     the    dirertive     imsc7ih;rie^  p,„  n^    y.      ^    ^ 
11' ig.    63,  D  and   I)'),  their  constit-      vkhsk  Skctk.n  <,k  aonactinia. 
uent  mesenteries  lying  one  on  each  A  //  =  diieciiv.-  moseiiifri.-s. 
>iide  of   the   sagittal  ])lano,  and  to-  ^'^^   =  *''*^^  Kdwunlsiiin  meseu- 
^vther  with  one  mesenterv  (//and  v  vr       ^*"'''"'"  :     , 
1)  iinm    each    of   the  other  pairs  imi.s  wi,i. //nnd  / 

represent    Mie    eight    Edwardsian         7  =  .secoiidaiy  i.uir  ..f  mcs- 
mesenteries.     To  these  six  primary  <'nieik',s. 

pairs  a  varying  number  is  added  in  the  difierent  forms-  it 
jnay  be,  on  each  si.le,  one  between  one  of  the  j.airs  of  dir.-c. 
ives  an.l  the  a.ljacent  lateral  pair  {Sr,jtn,>hnrm),  or  a  pair  in 
tl..  Han.e  locality  (r/omW/„m,  Fig.  (53,  7),  or  two  pairs  l.ne  of 
whirl,  corrosiKinds  to  the  pair  of  (ionardma,  the  second  pair 
lying  between  the  two  lateral  primary  pairs  {Ormii.s). 


112 


INVERTEBRATE  MORPHOLOGY. 


In  all  these  forms  there  is  a  strictly  bilateral  arrangement 
of  the  mesenteries,  and  a  tendencj'  for  them  to  arrange  them- 
selves in  pairs. 


6.  Order  ZoanthesB. 

The  Zoantliea3  form  very  frequently  colonial  aggregates 
either  of  a  diffuse  stoloniferous  character  (Zoanthus)  or  of  a 
more  compact  form,  the  individuals  being  imbedded  in  a  ca'- 
nenchyme  (Palyfhoa).  No  skeleton  is  present,  though  many 
forms  have  a  dense  crust  on  the  outside  of  the  body  formed 
of  particles  of  sand,   sponge-spicules,   radiolarian  and  fora- 

miuiferan    shells,  etc.,  imbedded 
in  the  outer  portion  of  the  meso- 
ghiea.      They    possess   a   varying 
number  of  simple  tentacles,  and 
1     there  is   only   a   single    siphonn. 
glyphe  which  marks   the  ventral 
surface  of  the  body.     The  mes- 
enteries are   arranged    in   pairs, 
six  of  which  (Fig.  G4,  /-  F,  //-  V/, 
///and  IV)  correspond  with  the 
six  i)rimarv  pairs  of  tlie  Protac- 
tinifo  ;  of  thesn  the  dorsal   direc- 
Fiu.  04.— Di\«;uAMMATic  TuANR-  tives  (/>)  are  never  united  to  the 
vKusK  Skction  of  Zoanihus.      .stomatodfPum     and     the     dorsal 

J),  I)   -  directive  nic'senterios.         ij        i         ■     /  rr    jr  rs  •    .         e 

T  ,,,      .  ,,      .  lateral  itair  (//,    I  I)  consists  of 

1-4  =  i)iiir,s  of  secundiiry  nicseu-   ""®    perfect    and   one    imperfect 
teries.  mesentery,  th«i  latter  being  ventral 

to  the  former.  The  ventral  lat- 
eral primary  pair  may  consist  of  two  perfect  mesenteries  or 
may  have  the  same  arrangement  as  tlie  dorsal  lateral  |)air. 
To  these  six  ])airs  a  varying  number  of  s<H'ondary  pairs  (I  h 
nniy  be  added,  tlie  new  pair  always  arising  ininuHliately  on 
either  side  of  the  ventral  dinuitivc^s.  Each  of  the  new  pairs 
consists  of  a  perfect  and  an  imperfect  mesentery,  the  latter 
being  the  dorsal  one  of  the  two,  the.se  secondary  pairs  thus 
dilleriug  from  the  lateral  primary  mesenteries. 


TYPE  CCELENTERA. 


113 


7.  Order  Hexactiniae. 

In  the  Hexactini!«  the  six  primary  pairs  of  mesenteries 

(Itiscnbed  as  ocTcurriug  iu  the  two  preceding  orders  are  again 

found  (Fig.  65,  /,  D,  and  D),  and  in  a  few  forms  {Halcampa) 

may  be  the  only  ones  present.     As  a  rule,  however,  a  varying 

nr       D 


Fio.  65.-DiAGnAMMATic  TnANHVEnsE  Skction  of  an  ITkxactinian   Aip. 

tnsia,  with  only  tho  meseuteiies  of  the  (ii,sl  cycle  perfect. 
1)  =  .lire:.ti ve  mesenteries.  r  =  .neseuteries  of  the  first  cycle. 

//=  reprodiiclive  region  of  mesentery.       // =  second" 

»«/=  mesenterial  tiliiment.  /// =  ..  .,     .<\^^^.^     „ 

unniber  of  secondary  pairs  develop,  each  of  these  appearing 
m  tho  interval  between  two  primary  pairs,  so  that  two  cycles 
of  mesenteries  (/  and  //)  may  be  distinguished.  Usually, 
however,  the  process  of  mesentery  formation  does  not  stcip 
liero,  tertiary  (///),  quaternary,  etc.,  cycles  being  developed, 
the  pairs  of  each  new  cycle  appearing  in  the  intervals  between 
1 1.'  pairs  of  the  cycles  already  present.  Consequentlv,  since 
tlicro  are  six  primary  pairs,  the  second  cycle  will  consist  also 
"t  SIX  pairs,  the  third  of  twelve,  the  fourth  of  twenty-four,  and 
«'>  on.  Iu  a  few  forms,  owing  to  the  precocious  development 
<>t  one  or  two  of  tlus  secondary  pairs  on  each  side,  the 
symmetry  becomes  converted  from  an  h«"xamerous  one  to  an 
octamerous  (Aiptasia  annulata)  or  a  decamerous  one  (Tealia). 

—  u..^  .!..|!  m  tonutritiwu  witxi  ine  spaces 

Ix'twoen  the  mesenteries,  they  are  arranged  iu  cycles  cone- 


-Sf*')ll8S«*4P'#t*aHBIBB 


114 


IN VEHTEBUA  TE  MORPUOLO G  Y. 


spondiug  to  the  mesenteries.  Usually  but  a  single  tentacle 
communicates  with  each  space,  but  in  some  forms  a  series 
may  arise  on  the  roof  of  each  sjjace  so  that  the  tentacles  have 
a  radiating  arrangement  {Discosoma)  or  may  appear  to  be 
irregularly  scattered,  as  in  some  corals  (Fwigia).  They  are 
usually  simple  in  form,  though  they  may  be  in  some  cases 
pinnate  {Phymanthus,  Thalassianthus)  or  even  branched. 
The  order  is  usually  divided  into  two  suborders : 

1.  Suborder  Malacodermata. 

This  includes  the  Sea-anemones  or  Actinians,  all  simple 
forms,  not  producing  colonies,  and  usually  attached  by  au 
adhesive  base.  They  never  form  a  skeleton  of  any  kind, 
though  they  may  develo^i  an  enveloping  cuticle,  usually  very 
thin  and  in  some  cases  encrusted  with  foreign  matter ;  this 
is  more  especially  the  case  with  deep-water  forms,  the  shallow- 
water  forms,  such  as  3Ietridiinti,  Bunodcs,  etc.,  lacking  a 
cuticle.  Many  forms  possess  the  power  of  division,  the  in- 
dividuals so  produced  separating  completely  and  not  formiiij^ 
colonies ;  furthermore  some  forms  reproduce  nou-sexually  by 
separating  oil'  portions  of  the  tissue  at  the  margin  of  the  base, 
each  portion  eventually  developing  into  an  adult  Actinian. 


2.  Suborder  Sdvrodennnta. 

This  suborder  includes  the  ordinary  corals,  which  secrete 
a  calcareous  skeleton  of  the  character  already  described 
(p.  107).  A  few  forms  are  sinii)le,  but  the  majority  produce 
complex  colonies  by  longitudinal  division  and  by  buddiu^s 
while  iu  others  the  division  is  only  carried  to  the  extent  of 
the  formation  of  an  individual  with  a  number  of  mouths,  as  in 
Fujigia  and  Manicina.  In  most  of  the  forms  the  corallum  is 
tolerably  dense  and  may  be  either  brandling,  as  in  (h'ul!7i<i,<)V 
form  massive  blocks,  as  the  Brain-stone  Coral  {MaHtndrinc), 
but  iu  3Iadrepora  it  is  more  or  less  |)orous. 

Tlio  Corals  arc  most  ahiiii(latit  in  tropical  seas  and  in  sliallowor  water, 
the  Madrepores  forminji  under  such  conditions  laryc^  reefs,  in  I  lie  laj^ooiis 
of  which  the  FmiKias,  Maiiicinas.  and  Ma'andrinasan^  found.  In  colder  s<;is 
i)Ut  few  forms  (Astratujht)  arc  found  in  shallow  water,  but  in  the  greulcr 


TYPE  CCELENTERA. 


115 


(Icptl.s  of  the  ocean  the  simple  forms  which  do  not  produce  colonies  are 
fiv(iuently  found. 

mationsMps  of  the  Anthozoa.-A^  has  been  pointed  out,  it  seems  prob- 
al.Ie  that  the  Anthozoa  are  to  be  traced  bacic  to  a  Scyphostoma-like  polvo 
lacknig  interradial  funnels.     No  four-mesenteried form,  however  is  knovv^i" 
a  large  gap  existing  between  the  Scyphostoma  and  the  Alcyonaria   which 
aio  probably  the  simplest  Anthozoa  known  to  us.    The  primitive  Alcyonaria 
wore  undoubtedly  simple  forms,  and  from  tiiem  to  the  Edwardsiie  was  not 
a  very  great  step.     By  the  formation  of  four  additional  mesenteries  tl.e 
Ldwardsian  condition  became  converted  into  the  twelve-mesenteried  con- 
dition which  forms  the  ground-form  of  the  Protactinia?,  Zoanthea-  and 
ll..xactinia3,  the  various  stages  seen   in   the  ProtactinijB  indicating   the 
manner  in   which  the   Ilexacti.iian  condition   has  been   brought  about 
'llie  Cerianthe*  seem  to  be  offsets  from  the  Edwardsian  condition  but  it  is 
diflicult  m  the  present  state  of  our  knowledge  to  conjecture  the  affinities  of 
the  Antipatharia. 

It  is  noticeable  that  the  members  of  all  the  orders  except  the  Ilexac- 
tinue  have  a  strictly  bilateral  arrangement  and  development  of  the  mesen- 
teries ;  this  arrangement  becomes  gradually  modified,  first,  by  the  ten- 
dency of  the  mesenteries  to  arrange  themselves  in  pairs ;  second  by  the 
formation  of  secondary  mesenteries;  third,  by  a  tendeiicv  for  these  to 
appear  in  pairs  ;  fourth,  by  a  tendency  for  such  pairs  to  appear  in  all  the 
intervals  between  the  primary  pairs.  Thus  the  Anthozoa  are  forms  which 
are  gi-adually  specializing  away  from  the  radial  symmetry  characteristic 
of  all  Coelenterales  towards  a  bilateral  symmetry,  and  the  more  pronounced 
radiality  of  the  Hexactinije  is  a  secondary  condition. 


SUBKINGDOM  M?]TAZ()A. 
TYPE  V  (EL  EN  TEH  A. 

Subtype  FORI FER A. -With  pores  in  the  walls  and  without  nomato- 
cysts. 

1.  Order  CV/fca/'ea. —Skeleton  calcareous. 

{a)  Ascon  type.     Leucosolenia. 
(h)  Sycon  type.     Qrantia. 

2.  Order   CormimspoiKjuc-Skdaion  of  spongiolin,  usually  with 

simple  siliceous  spicules. 

(_<()  With  spicules  ;  fresh  water.     S/migilla,  Ephyihitia. 

(6)  Without  spicules  ;  marine.     Enspotujia. 
8.  Order  Spiculisfxmi/itr.—iikch^um  of  uniaxial  or  tetraxial  sili- 
ceous spicules.     Sometimes  entirely  wanting. 

(a)  Skeleton  wanting,     llalisarca. 

(b)  Skeleton  present.     Clhna,  Esperella. 

4.  Order   Hyalo.sponyue.— Skeleton    of    0-rayed  siliceoua   spicules. 
Eitplwtella. 


116 


INVERTEBRATE  MORPHOLOGY. 


11.  Subtype  CNIDARIiV.  Without  pores  in  walls  and  with  nematocysts. 
I.  Class  HYDROMEDUS.E.— Ectoderm  and  endoderm  meet  at  mouth.     Re- 
productive o-xHiis  develop  in  ectoderm.    Medusa  with  velum ;  sense- 
organs  not  moaitied  tentacles. 

1.  Order  Uydrariix.—^o  medusa  form  ;  tentacles  hollow.    Hydra. 

2.  Order  Narcomedasa.-^o  hydroid  form;  sense-organs  otocysts 

of  endodermal  origin ;   radiating  canals  represented  by  broad 
pouches.     Cunoctantha,  Cunina. 

3.  Order  Tra<:hfjmedusix.—^o  hydroid  form  ;  sense-organs  otocysts 

of  endodermal  origin  ;  radiating  canals  narrow.     Liriope,  Ger- 
yotiia,  Rhopaloneina. 

4.  Order  Leptomedasa;  or  Campamdarice.— With  both  hydroid  and 

medusoid  forms,  the  latter  frequently  degenerate.     Hydrantlis 
witli  hydrothecte  ;  gonangia  present.     Medusa  with  otocysts  of 
ectodermal  origin  ;  reproductive  organs  on  radial  canals, 
(rt)  Hydroid  and  medusoid  forms  both  well  developed.     Eu- 
cope,  Obelia. 

(6)  Hydroid  form  not  well  developed,     ^quorea,  Rhegma- 
iodes. 

(c)  Medusoid  form  degenerate.    Sertularia,  Halecium,  Aylao- 

phenia. 

5.  Order  Aiit/iomediisa;  or  Txhnlnrice.    With  both  hydroid  and  me- 

dusoid Conns,  tlie  latter  freiiuently  degenerate.     Hydroid  foiiiis 
without  hydrotheote  or  gonangia.     Medusoid  forms  with  e\i- 
spots  ;  reproductive  organs  developed  in  wall  of  manubrium." 
(a)  Medusoid  form  well  developed.     Margelis,  Coryue,  Fen- 

liar  la. 
(6)  Medusoid  form  degenerate.    Clava,  Hydractinia,  Tubu- 
laria,  Eiidendrium. 

6.  Order  Hydrocoralliiue.-Wyavoxii.  forms  polymorphic ;  secreting 

calcareous  siveleton  by  ectoderm.     Medusoid  forms  usually  de" 
generate.    Mi/lepora,  Stylaster. 

7.  Order  Hiphonophora.—Yvini-^wxmmmg.  pelagic,  polymorphic  col- 

onies. 

(ff)  Nectocalyces  present,  without  pneumatophore.     Bipfiyts. 
(6)  Willi  both  nectocalyces  and  pneumatophore.     Ayalma. 
{o)  With  pneumatophore  only.     Caravella. 

(d)  Discoidal  forms  without  nectocalyces.     Velella,  Porpita 
ScvPHuMKi)iJs.i;.  — With   medusoid  form    only   in   adult   sla-r, 

Velum   not  present;  sense-organs  are  modified  tentacles.      Keimi- 
ductive  organs  develop  in  endoderm. 
1.  Ovdiiv  Stauromednsa:—\\\\\\  the  eight  primary  tentacles  not  .it 

all  or  but  slightly  modified.     Tessera,  Lucernaria. 
a.  Order  Peromedum'.—W ii\i  the  four  interradial  primary  tentacles 
transformed  into  sense-organs. 


II.  Class 


TYPE  CCELENTERA. 


117 


3.  Order   Cuhomedus<..^WM.  the  four  radial   primary  tentacles 

tiausformed  into  sense-organs.     Charyhdea 

4.  Order  Discomedus,^.-mth  all  eight  primary  tentacles  trans- 

formed  into  sense-organs, 
(a)  Mouth-lobes  not  fused.     Cyanea,  Aurelia,  Pelagia. 
T,T    ^,  ^  ^         ''  mouth-iohes  fused.     IStomolophus 

todoeum  ;  coelenteron  divided  into  chambers  by  vertical  mesenteries  • 

reproductive  organs  developed  in  the  endoderm  ^^'enteries  , 

1.  Order  ^/cyo^ana.- Colonial  forms  with  eight  mesenteries  not 

ai ranged  in  i)airs  ;  tentacles  pinnate. 

(a)  Without  axial  skeleton.     Penma.  Alcyonium,  Pennatnla. 

{b)  With  axial  skeleton,     aorgonia,  Leptoyorgia,  Ms,  Coral- 

Itnm. 

(c)  With  tubular  calcareous  skeleton.     Tuhipora 

2.  Order  ^rf«.«,v/,,/«.. -Simple  forms  with  eight  mesent'eries  not  ar, 

ranged  in  pairs  ;  tentacles  simple.     Edwardsia 

3.  Order  e.;.-a»Y/..a..-Simple  forms   with   numer(;us   mesenteries 

not  arranged  in  pairs  ;  new  mesenteries  formed  on  each  side  of 
dorsal  mid-line.     Cerianthm. 

4.  Order  ^«^,>a^/,a,,-„,._CoIonial  forms  with  axial  horny  support  ■ 

6.  Order  Protactinic,.-^un^\^  forms  with  twelve  primary  mosenter- 
los  arranged  in  pairs,  and  in  addition  one  unpaired'me^^t; 
Omc^f!  '    ''  ''  ""'  ''  '^"  ^'""''^-    '^^•^^^^^/'-•"•^•.  Go„actinil 

'6.  Oi^er  Zoanmec..-H\nn.h  or  cobnial  forms  with  twelve  primary 
niosent.nes  arranged  in  pairs,  and  in  addition  a  varying  n,  „- 
ber  ot  secondary  pairs  developed  on  each  side  of  the  primary 
pair  occupying  the  n.id-ventral  line.     Z,>antU„s,  Palytkoa 

7.  Older  Hem,tunw.-^■nx^^A,,  or  colonial  forms  with  twelve  nri- 

Zirof'"''""/'"'"""'''  '"  ^"""'  "^'^  '"  '''^"'''-^  -  variable 
umbel  of  secondary  pairs  arranged  in  cycles,  the  newer  pairs 

d  veloping  in  the  intervals  between  the  pairs  already  pre  et 
An  external  calcareous  skeleton  present  in  many  forms 
(a)   Without  calcareous    skeleton    {Malacodennnta)       Hal- 
/M  xvT'^'":  ^'^'^"•"■«'  ^^«^'«'  Metridium,  Bunodes. 
(6)  W  ith  a  calcanM,us  skeleton  merodennata).    Madrepora, 
J^unyia,  Manicina,  Mwandrina,  Astraugia 


118 


INVEKTEBHATE  MOIWHOLOQT. 


Leip- 


LITERATURE. 

A.    PORIFEUA. 

Vosmaer.    Porifera.    Bronn's  Klassen  und  Ordnungen  des  Thierreichs, 
zig  u.  Heidelberg,  1887. 

E.  Haeckel.     Die  Kalkschwamme.     Berlin,  1872. 

F.  E.    Schuize,     UntersuchuiKjen   iiber  Ban  und  Entwicklimg  der  Spongien. 

Zeitscbr.  fl\r  vviasenscb.  Zoologie,  xxv-xxxv.  1876-81. 

A.  Dendy.     Obnerxations  on  the  titracture  and  Classification  of  the  Calcarea 

heteroca'ld.     Quarterly  Journal  of  Microsc.  Science,  xxxv.  1893. 

B.  von  Lendenfeld.     A  Monograph  of  the  Horny  Sponges.     London,  1889. 

r.  E.  Schuize.     lieport  on  the  llexactinellidce.     Reports  on  tbe  Scientific  Results 
of  tbe  Voyage  of  H.M.S.  Cballenger.     Zoology,  xxr.  1887. 


G.   von  Koch. 

iMonogr.  x\ 
A.  von  Kdlliker, 

VII  and  VIII 
6.  Brook.     Itcpo 

tbe  Voyage 
A  Andres.     Le  . 

IV.  1883. 
0.  &  R.  Hertwig. 

isebe  Zeitscli 
J,  P.  McMurrich. 

1891. 


B.  Cnidakia. 


GENERAL. 


L.  Agassiz      Ccntribvtions  to  the  Natural  History  of  the  United  States.    Vols. 

Ill  and  IV.     Boston,  1860-62. 
A.  Agassiz.     North  American  Acaleplm.     Illustr.  Catalogue  of  tbe  Museum  of 

Comp.  Zoology,  ii.  Cambridge,  Mass.,  1865. 
E.  MetschnikofiF.     Embryologische  Studien  an  Medusen.     Wien,  1886. 
0.  &  R.  Hertwig.    Das  Nervensystem  und  die  Sinnesorgane  der  Medusen 

Leipzig,  1878. 


Ray  Society. 


HYDUOMEDUS/E. 

G.  J.  AUman.     A   Monograph  of  the  Oymndblastie  Hydrcids. 
London, 1871-72. 

E.  Haeckel.     System  der  Medusen.     I.  Graspedoten.    Jena,  1879. 

H.  N.  Moseley.  Report  on  certain  Hydroid,  Alcyonarian,  and  Madreporarian 
Corals.  Reports  of  tbe  Scientific  Results  of  tbe  Voyage  of  H.M.S.  Chal- 
lenger.    Zoology,  II.  1881. 

W.  K.  Brooks.  The  Life-history  of  the  Hydromedusm.  Memoirs  Boston  Soc. 
Nat.  Hist.,  III.  1886. 

A.  Weismann.    Die  Entsteliiuig  der  Sexualzellen  bei  den  Hydromedusen.    Jena 

1883. 
H.  V.  Wilson. 

ral  Stages. 

IV.  1886. 
E.  Haeckel.     lieport  on  the  Siphonophorw.     Reports  of  tbe  Scientific  Results  of 

tbe  Voyage  of  H.M.S.  Cballenger.     Zoology,  xxviii.  1889. 
A.  Agassiz.     The  Porpitidw  and  VdcllidiB  of  tlie  Gulf  Stream.    Memoirs  Mu- 

seum  of  Coinp.  Zoology,  viii.  1883. 


The  Structure  of  Cunoctantha  octonaria  in  the  Adult  and  Lar- 
Studies  from  tbe  Biol.  Laboratory  Johns  Hopkins  University, 


SCYPnOMEDUS^. 

S.  Haeckel.    System  der  Medusen.     II.  Acraspeda.    Jena,  1880. 


TYPE  C(ELENTEliA. 


111> 


ANTnOZOA. 


G.   von  Koch.     Lie  Oorgoniden.    Fauna    u    Flor,.  a      «  ,/ 

iMonr.gr.  xv.  1887.  ^'*''^*  <^«s  Golfes  von  Neapel 

A.  von  KOlliker.     Die  PennatuUden.     AbLandl   '^Pn.i.     , 

VII  and  viir.  1872.  ^'^iiandl.  feenckenbiirg.  Nat.  QesellscL., 

6.  Brook      7?.^;c;;-<,,,,  ^/^c  ^«<*>«</,«n«.     Reports  of  tl..  «  •     .-. 

tbe  Voyage  of  H.M.s.  Cballenirer     7on.  Scientific  Results  of 

A  Andres.     Le  Attini,      v.  7'r.,  '^''"'"^'^'  •^'-^■^"-  1889. 

rx.  1883  "^""     "^"'""^  ""'^  ^^-^  ^-  «olfes  von  Neapel.     Monogr 

"■  ''i^'^r^f'';^''  "'"^^'"-^  ««^  ^-'<>%-^  .«.«•...,     Jena- 
.P.^M^MurriC.     .'/.  ,V.,.,..,  .,,,,  ^,,_.     Journal  of  Morpbolog,.  ., 


lao 


iJV  VEliTKBUA  TK  MOIWUOLOU  Y. 


CHAPTER  VI. 


TllK  crrKNOlMlOKA. 


Thk  group  of  forms  known  ns  ilio  Ctonopliora,  to  wliicli 
the  sjHtoniatic  vnluo  of  ji  rliiss  iniiy  In;  }j;iv(Ui,  j)r('8('nt  no  littlo 
gonoral  restMuhliuuH^  to  tlui  (-(MltMitiM-a.,  but  ut  tlio  siinu)  tiiiio 
ili'part  so  wiilely  in  struoturul  juul  liistologieul  chjiructcrs 
fnun  tlui  (hiicliiria  and  Porifora  that  it  hcumiis  a(lviHaI»lt>, 
until  further  cvidouco  is  forthconiinj^,  to  consider  them  as  a 
grou})  a})art. 

Ail  the  Ctenophoros  are  pela}j;ic  and  are  of  groat  trans]i;i- 
renoy  and  delicacy,  due  to  the  nature  of  the  mesoglaial  tis.siu!. 


mo 


Fig.  QCy.—Iioltna  hyihxtina  (after  Cih'nV 
cp  =■  ciliatod  pliUi's.  tc  =  fuiinel-ciuml. 

g  =  stomach  or  t'uunel. 

I  =  lobe. 


<nic  =  stoinoiin.'al  canal. 


lu  form  they  vary  greatly,  some  being  almost  spherical  or 
pyriform  {Pleurohrachia),  sometimes  with  broad  lobes  ])roj(H't- 
iug  from  near   the  oral  extremity  (Fig.  ()t5,  ?)  {BoJina,  Afmiiu- 


<)/)si.s),  otiiors 
oUiers  sa(!-li 
sviinmitry  ur 
|ilates  (cp)  wi 
into  the  bac 
The  stomodii 
c.ivity  {(J)  ill  , 
I'll  (iach  sido  ( 
lilt)    according 

stoinodjlMlIii,  ; 

and  corrosix)! 

TJu)  nioiitl 

is  dirocted  ba 

(Icrnial  stonnx 

I'l.'iiic.     At  its 

•  linlci-injii  gjist 

liv(!  canals  ari; 

llni  aborai  siirl 

liy  usually  two 

with    the    broji 

I'liiidly  ;  while 

wards  in  the  ti 

'il"  the   tentach 

^'iviiig  ofl"  two 

soon  divide   an 

'ii<'ate  periphci 

the  rows  of  <•■///> 

These  plate; 

arranged  one  al 

arising  from  ect 

ional  rows  of  th 

each  row  a  d(di 

towards  the  abo 

"»»*   as   tliey   a] 

reduced  to  four 

il  'Inme-shaped 

to^^!thor  at  the  c 

wicldsed  is  Hom 

transverse  axis  ai 


riK  cTKNimmiu. 


121 


../™.),  <.tl,„rH  I„„„K  ,il,l,„„-]il<..  as  «.,,/„,„,  t|,„  V„„„.s-  .-i,.,)!,. 

«v,u„„,t,.y  ,.,.0  s,.,.„  in  tho  ,.i«|,t  l.,„Kit,„l,„.l   I |       f         .  ' 

H|'to«  c,,  wh„.l,  »„„„  ,„  |„„,„„„t„,  „  I  '  ;  - 

"   ■>    t...   l..u-kK-n.„l  by  tho  „„„■„    ,„",„„„„,.,„1     ,      t    :" 
I  i.o  »t,„„.Kl„„„,,    ,„   „,u„„„,,  i„   ,„„^  M,     „  s    ■<■' 

'■■■»it.v  (I/)  n,  a  pla,,.,  at  n'Kht  anf.|„s  l„  this  tiv„  t  .„      I 

;■';  ""'^''  -,'" "[ " .V.  iyi..«  ;:,»„  h,  thir;"t  :',:::," 

l">    HC,».nl,„(,b-   t"  .•.■«w,i.„    a    sa„ittai     ,  la,„.     Ih    t    „      .T 
'"". "■■■-  •■";!'  ■'  '™-e..s„  ,,h.„„:that  „!■  t      «a        .      v    " 

Tlu!  nu.uth  lie.s  .-it  t],o  oxtr«>initv  of  the  vfufi....!       •       i  •  , 

r  ;'"'7";"  '"";'"-'•«  ■•-  '"-■",.,• li ,, :  :•  ;i,: : ' 

'';"'""'  »"".'•>''-"■".  «hh.|,  is  Halt,., ,,a.alh.l  t„  th,     v  it    l" 

;' "■ «''»"■-  -"'.V  (,/,  ...■  s„.,.ali,„l  "f„    „, .1  "  ,       ,,      : 

i,  us„any  tw.,  „,„.„i„„s  ;  two  oth..,.  pass  iw.nval  pa r  i 
»;n,    the   l„.„a,l   surface   of  th,.   sto  no,h,.,„„    („  .     .  " 

l'l""ll.>-;  whih,  th„  „th,„-  t,vo  (Fi,,  ,;7  „.      '  ;    .    ■"'   '""' 

f  t lo  I  r  '■'"'"■"■'T """ '■'  "■" 'y -'•  "'"•  •■"  'I'-' i«  1 

vi       ,^  ti      ;■  '  ,       ■'  ''"'■"""  ''"'■■"■"  "-■'■  ton„i„ati,„ 

"'""*',•','       ''™'"l"-«.  ""< .ach  si,l„.     These  hrujohes 

»">'  'I'vule   a,„l  Kive  nse  each  to  t,vo  ca„als  wh  cl  ,     u 

;i::t;,::;';^:::X:"'  -"'" -  "-.i-n,::;,;  hZ 

These  i-lates,  whi,.h  coastitnte  the  loc,„„„tor  or.-an,  are 
...n,n.e,l  „uo  above  the  other  and  are  con.pose.l  of  fn^se  , C'  a 
"ns.nf!  fro„,  ecto,h,r,„al  thicke (,».     There  are  ei,  U 

-1.  row  a  ,lel,cate  groove  line.l  with  ciiiate,!  ce'l      e2 

'  "••"■(Is  the  aboral  pole,  each  groove  nuMin^  with  au  a,H ace 

"«■>   lis    tlioy   approach    the    pole    so    tl,.,t    tl,  "'>>«'' 

leduceato  four  (Fi.,  C7  c«1      T,  '   """''""'  '" 

111  l,ii„.  ij(,  est),      lliese  pass  m  upon  the  floor  of 

I  me-shaped   cavity  euelose.l    by  fuse.l   ei  ia  which   ^r 

ludsccl  IS  Homuwhiit   brojuler  in  the  Hauii^-A   fl,..n    .•      xi 
".-verse  axis  and  coutaius  the  aboral  seultl^ltl  'The'al':: 


122 


INVKRVKBllA  TE  MOUrilOLOG Y. 


of  the  cavity  is  foinietl  of  liigh  ciliated  cells  probably  uervous 
in  fuuctiou,  and  above  tlieru  is  a  mass  of  otoliths  suppoiicd 
on  fonr  incurved  rods  of  fused  cilia,  one  of  which  forms  tlie 
termination  of  each  of  the  four  meridional  grooves. 

In  addition  to  this  sense-organ,  \vhi<!h  is  to  be  regarded 
as  of  the  same  function  as  the  otocysts  of  the  medusie,  there 


Fig.  Ql.—Pleurobmchi'ii  sken  foh  the  Abohal  Pole  (after  Aoassiz). 
eg  =  ciliiited  groove.  p  =  polar  urea. 

ot  =  otocyst.  re  =  radial  caual. 

t  =  tentacle. 

lies  at  each  end  of  the  sagittal  axis  of  the  sensory  dome  a  so- 
called  pole-area  (Fig.  C7,  p),  the  cells  of  which  are  furnislietl 
with  small  plates  of  fused  cilia,  each  area  being  surrounded 
by  a  thickered  ciliated  rim.  These  structures  are  from  tlieir 
form  and  situation  supposed  to  be  sensory,  and  an  olfactory 
function  has  been  attributed  to  them. 

The  tentacles  (Fig.  <)7,  t),  of  which  there  are  two,  situated 
at  the  extremities  of  the  transverse  axis,  are  present  in  all 
forms  except  the  Beroids.  Each  tentacle  lies  in  a  ilee]) 
depression  termed  the  fenfacle-fiheath  and  consists  of  a  princi- 
pal axis  which  gives  rise  to  a  large  number  of  secondiuv 
tentacles  arranged  upon  one  side  only.  Both  the  priniiuv 
axis  and  the  secondary  tentacles  are  solid,  being  composed 
mainly  of  muscle-cells  and  containing  no  prolongation  of  the 
tentacular  vessel.     In  3Inemiopsis  and  its  allies  and  in  Cestum 


THE  VTENOPIIOUA. 


123 


Fio.  68.-AoniisivK Cells 

KltOM     TkNTACLK     of    A 
CtknoIMIOKK  (after  Chlt.nj. 
c  =  julliesive  cup. 
in  =  contractile  stalk 


th.i  i)nmary  axis  is  pruoticullj  wiintiiif,',  the  secondary  tentacles 
ansinj^'   directly   horn    the    bottom    of 
the  tentacle-sheath.     The  ectoderm  of 
tlio   secondary   tentacles  contains    nu- 
iiH'ioiis  cells  Hup})osed  to  be  sensory, 
and  also  so-called  (Jhesive  cells,  which 
ill  this  ^'ronp  replace  the  nematocysts. 
Thoy    consist   of    a   slender    spiral  ly- 
coiltul   muscular  fibre   (Fig.  (58,  m)  at- 
tiicliod  at  one  extremity  to   the  subja- 
cent   tissue    and  terminating,'    at    the 
other  on  the  under  surface  of  a  hemi- 
sphcu'ical    cap   (c),    whose    surface    is 
covered  by  small  spherical  masses  of 
a  sticky   secretion.      A   small  auinnil 
comin<,'  into  c(mtact  with    these    caps 
is  hohl  by  the  adhesive  secretion,  the  muscle-fibre  being  suf- 
iiciently  elastic  to  yield  to  the  struggles  of  the  victim  and  to 
bruig  It  in  contact  with  the  general  ectoderm  by  contracting 
when  its  struggles  cease. 

The  reproductive  organs  lie  in  the  outer  walls  of  the 
canals  which  lie  beneath  the  meridional  rows  of  plates,  but 
apparently  are  originally  derived  from  the  ectoderm.  All  the 
Oteu()phores  are  hermaphrodites,  the  ova  being  arranged  on 
one  side  of  each  canal  and  the  spermatozoa  on  the  other,  in 
such  a  manner  that  the  adjacent  sides  of  any  two  canals  bear 
the  same  kind  of  sexual  cells.  A  peculiar  phenomenon 
termed  Dissogonu  lia«  l)een  observed  in  certain  forms,  consist- 
nv^  of  the  occurrence  of  two  periods  of  sexual  maturity  in  the 
hfe-history  of  the  individual,  the  reproductive  organs  ripening 
tiist  while  it  is  still  in  a  larval  stage  and  again  when  it  has 
readied  its  adult  form. 

The  main  bulk  of  the  body  of  a  Ctenophore  is  made  up  by 
a  gelatinous  tissue  intervening  between  the  endoderra  and 
ectoderm  and  which  may  be  termed  the  mesoghjea,  though  it 
IS  not  improbable  that  its  cellular  elements  are  in  great"part 
derived  from  embryonic  cells  corresponding  to  the  mesoderm- 
cells  of  higher  forms.  It  consists  of  a  gelatinous  matrix- 
through  which  are  scatte:-d  branched  cells  and  fibres.     Some 


124 


IN  VERTEBRA  TE  MORPIIOLOG  Y. 


of  the  latter  extend  throughout  the  entire  thickness  of  the 
luesogloea  and  are  inserted  by  their  branched  extremities 
into  the  ectoderm  on  the  one  side  and  the  endoderm  or 
stomodieal  ectoderm  on  the  other.  They  are  contractile  in 
function,  consisting  of  a  central  i)rotopla^mic  axis  containing 
u  nucleus  and  of  a  peripheral  contractile  substance.  In  addi- 
tion to  these  there  are  other  much  tiner  fibres  which  have 
been  supposed  to  be  nervous,  and  on  tlie  outer  surface  of  the 
niesogltea,  between  it  and  the  bases  of  the  ectoderm- cells,  is 
a  network  of  stellate  ganglion-cells  whose  i)rocesses  overlap 
but  do  ut)t  unite  with  each  other.  They  are  esi)ecially  abun- 
dant in  the  region  of  the  meridional  rows  of  plates ;  just  us 
the  slender  fibres  of  the  mesogki^a  are  especially  abundant 
below  the  aboral  sense-organ  and  the  meridional  grooves, 
regions  wliich  reeeut  observations  liave  sliown  to  be  especiullv 
sensitive  to  stimuli. 

The  class  may  be  divided  into  two  orders : 


1.  Order  Tentaculata. 

The  members  of  this  order  possess  tentacles  either  with 
or  without  the  primary  axis.  The  simple  forms,  such  as 
Fh'Ht'ohvdi'kiu,  belong  to  this  order,  as  well  as  the  lobate  and 
ribbon-shaped  forms.  In  the  lobate  forms,  such  as  lioJiiui 
(Fig.  ()6)  and  Mnemiopsis,  there  is  at  each  end  of  the  sagittal 
axis  a  large  lobe  developed  into  which  four  of  the  meridional 
canals  are  continued  ;  two  of  the  canals,  those  nearest  the  ex- 
treujities  of  tlu^  ti-ansverse  axis,  pass  around  the  edge  of  the 
lobe  and  unite  with  each  other,  while  the  other  two,  whicli 
also  unite,  are  thrown  into  arabes([ue-like  twistings.  'J'he 
Yeiius'-girdle,  Ce.s(KiH,iH  ribbon-shaptul,  being  flattened  in  the 
transverse  plane  and  much  drawn  out  in  tlie  sagittal  ])lane; 
the  result  being  the  great  extension  of  four  of  the  meridional 
plate-rows  and  th(^  almost  complete  disap])earance  of  the 
other  four.  In  its  young  stages,  however,  CeMum  is  a.  sph(  i- 
ical  foi-m  closely  resombliug  the  sim})Io  genus  Mertemia. 


THE  CTENOl'IWliA. 


125 


2.  Order  EurystomesB. 

This  order,  which  includes  the  Beroicl  forms,  is  character- 
1/0,1  by  the  eutire  absence  of  tentacles  and  by  the  wide  bell- 
ike  stonuKheuni.  Tlie  meridional  canals  send  oft'  alon.^ 
their  course  numerous  brancliin^r  p,ocesses  iiito  the  meso^la^a 
uml  are  united  around  the  mouth  by  a  circular  canal.  To 
tins  order  belongs  the  Mediterranean  genus  Beroe,  and  the 
^;onus  Idyui  of  the  northwest  Atlantic. 

Rdationshipsofthe  Vtenophora.~'Vh^  Ctonophoros  luive  been  i,y  niu.t, 
.n.  hors  assigned  to  the  type  Cu^Ientera.  on  aecount  of  tl.eir  jelly-like  cm  - 
s.  eney  and  tlu3  prosonce  ot  gastro-vascular  eanals,  and  ot  nulicitions  uL 
..l.a.e  symmetry       t  ,s  possible,  however,  that  these  oharaeters  are  sin. 

I  !; 'ri;,'!:"'';"'  T  ^'r^  ^•""^'  l-sesses  but  very  remote  ailinities  to. 
ilio  Ca-lentera  OS     They   have  furthermore  been    regarded   by  some   as 
n.nnec  n.g  lu.ks  between   the  Co>!en(erates  and  the  Turbellarians,  and  h 
-nneeUon  w.th  tins  idea  two  aberrant  fonns  n.ay  be   brieHv  described 
^n.Uemi^,„a,  .s  a  flattened  forn.,  on  the  n.i.ldle  of  whose  chu'sal  s..rfaee 
..s  he  ot,,l.ta  sac,  and  at  a  s  ,.rt  distance  from  this  are  eight  short  rows  of 
'  ilM-pI.i  es  each  u,  a  slight  d..p,,>ssion.     Two  tentacles  lie  in  the  transvers,» 
;ix:s,  and  the  month  .s  sitnate<l  at  the  centre  of  the  lower  surface  and  lea.ls 
n.  oacav.ty  from  which  nnn.erons  branching  gastric  pouches  arise  w  t   - 
-It  any  dehn.te  arrangen.ent.     The  other  form,  Ca^loplana,  i«  also  Hat- 
;.H'd  and  creep„,g  ;  ,he  n.outh  lies  on  the  under  surface  and  opens  i.Uo  a 
"   i.  cav.ty,  which,  as  .n  ateuoplana,  gives  origin  to  a  nund.er  I.f  pouc-hcs 
wli.ch  branch  an.l  give  rise  to  a  network  towards  the  periphery  of  the 
•",ly  ;  a  canal  passes  from  the  gastric  cavity  towards  the  dorsal  surface  ..f 
li.-  I.<.<ly,  where  it  divides  int..  two  branches  which  end  blindly,  and  lying 
"'tween  them  ,s  a  vesicle  ....utaining  otoliths;    (w<.  t,.nta,.les  similar  to 
•  linse  of  I le„rohrachin  lie  in  the  transverse  axis.     In  b..th  these  tonus  Hie 
f-'nieral  surface  of  the  Irndy  is  ciliate.l,  and  they  seem  (o  n.present  inter- 
'N".l.ate  forms  between  the  Ctenophores  au.l  Turbellaria.  ('tn,oi,lana  being 
more  closely  allied  to  the  f..rmer  and  Vnloplam,  t„  the  latter 

There  are  vari.,us  in.porfant  structural  differences,  lu.wever,  betw.cn 

<•     .eh.ntera  an.l   the   (',.>u.,phores.     AuuHig  these   nuty    be  n.entione.l 

.'  structure  and  p..s,ti..u  of  the  sense-organ,  the  structure  an.l  position  ..f 

-  mes..gl,eal  musele-libn.s,  the  structure  of  (he  t.M.tacles,  the  ptvsence  of 

tlH'  a.lh.'s.ve  cells  which  cannot  possibly  bo  homologized  with  nemafM-vst- 

Hls.  an.l  finally  the  early  .litr..n.ntiati..n  in  flu,  on.bryo  of  cel|«,  rese.nbiing 

0  uu.s.,.lerm-eells  of  (riploblasti,.animals.  which  giv.-  rise  to  the  muscles  of 

III!'  tentacles  and  ixTJuips  to  some  .if  (h.^  !!iivi,'tt.-{,y=,|  -.■  ;     ,  t_ 

It  seoms  not  improbal.l,.  that  fhe  HUlnitieH  orihJ'cfon.mhores  woul.l  b.. 
'Mniv  accurately  indi,.a(ed  i.i  the  cla.ssiflcafi..n  iffhoy  wore  onf  irely  removed 


126 


IN  VERTEBRA  TE  MORPIIOLOO  T. 


from  the  Coeleiitera  and  associated  with  the  TurbeUaria,  being  regarded 
as  highly  modified  forms,  adapted  for  pehigic  life,  descended  from  Tur- 
bellariau  ancestors.  The  evidence  which  lias  been  brought  forward  in 
favor  of  a  relationship  of  the  TurbeUaria  to  the  Ccelentera  througii  iht; 
Ctenophores  would  support  this  view  as  well  as  that  it  was  intended  Ut 
support,  and  to  this  may  be  added  the  fact  that  while  the  peculiar  adhesive 
<;ells  of  the  Ctenophores  cannot  be  homologized  with  any  of  the  histological 
•elements  of  the  Cnidaria,  they  may  readily  have  been  evolved  from  (ho 
adhesive  cells  which  occur  in  the  ectoderm  of  many  Turbellarians. 


SUBKINGDOM  METAZOA. 

Class  Ctenophora.— Pelagic  organisms  provided  with  eight  meridional  rows 
of  plates  formed  by  the  fusion  of  cilia. 

1.  Order  Ten.tamlata.—V,\{t\m\)\w\-A  provided  with  tentacles. 

(a)  Without  lobes ;  more  or  less  oval  in  shape.     Pleurohrachia, 

Mertensia. 
{b)  Lateral  lobes  occurring  at  oral  pole.     Bolina,  Mnemiopsis. 
(c)  Kibbon-like  form.     Cestum. 

2.  Order  EKrystomiiv.—yiWXumi   tentacles ;    stomodajum   wide    aud 

bell-like,    lie  roe,  Myia. 

LITERATURE. 

K.  Hertwig.     Ueher  den  linu  der  Cteiiiphoreu.     Jenaisolie  Zeitschr.,  xiv.  1880. 
C.  Chun.     Die  Cteiiophoren  des  (io/fes  von  Neapcl.     Fauua  uud  Flora  des  Golfes 
vou  Neapel.     Monogr.  i.  1H80. 


TYFE  PLATYUELMINTHE8. 


127 


CHAPTER  VII. 


TYPE  PLATYHELMINTHES. 

The  Platjlielmiuths  constitute  a  group  wliicli,  though 
preseuting  a  much  liigher  grade  of  orgauizatiou  thau  the 
(.Jd'leiitera,  nevertheless  show  certain  general  structural 
similarities  to  the  representatives  of  that  type.  Thus  upon 
the  exterior  of  the  body  there  is  a  thin  ectoderm  (Fig.  09, 


^      b'm   vd  n 

Fid.  OO.-DiAOHAMMATic  TuANHVKtiRR  Srctionh  Tnnomn  vARiors  TimnEi  • 
i-AiMA  A,  m  Aci-lan  ;  li,  a„  AllcioccHan  ;  C,  a  Hl.abdocu'lun  ;  D,  a 
1  riclud. 

bm  -  hasonu'iit  inembianc  o  =  nvarv. 

rf  =    iulL'Sli.lC.  od  =    OVidilil. 

ec  =  (.ct.ult.rm.  ^  ^  pairnchvine 

m  =  niusclclayer.  t  =  tentis 

"  =  '"^^••^^'  V  =  vitdlarimu. 

vd  =  vns  defert'iis. 

/>.  re),  below  which  is  a  fxrscneuf-mi'mhranr  (hni)  sometimes 
till..,  strnctureiesH,  and  destitute  of  cells,  sometimes  thicker 
H...1  enclosing  branduMl  cells,  and  strictlv  comim.able  in  iha 
uu'so^hvn  ,>f  the  (;..>lenterates.  AVitl.in  the  basement-men- 
hiMi.o  there  is  a  compact  mass  .»f  tissue  surrounding,  i„  the 


128 


IN  VERTEBRA  TE  MORPllOLOG  Y. 


majority  of  furius,  a  cavity,  the  eiiteroii  {d),  the  cells  liiiiiij. 
the  walls  of  this  beiug  dirterentiated  into  a  cli<,a^stive  epithe- 
liuni  ov  eiulodenii.     The  space  between  the  euteron  and  tluj 
basenient-inenibrane  is  occupied  by  the  mesodenn,  consistiiifr 
l)eii])lieially  of  compact  layers  of  circular  and  loiigitudi-^  I 
muscle-libres  {m),  whih>  below  these  it  forms  a  mass  of  nu- 
cleated cells,  usually  vacuolated  so  as  to  resemble  a  network 
of  libres  enclosinj--  spaces  and  constituting,^  the  pumichi/nia  (p). 
It  is   traversed    by  dorso-ventral  muscle-libres  and  iuis  im- 
bedded in  it  various  or<,'ans  most  of  which  are  further  dif- 
ferentiations of  this   middle  germ-layer.     These  two  layers, 
the  emloderm  and  mesoderm,  are  together  comi)arable\vith' 
the  inner  layer  of  the  Cielenterates,  the  mes-endodern),  and 
when  the  enteron  exists  it  communicates  with  the  exterior,  as 
in   that  f^roup,  by  a  sin«,de  oj)(>nino-,  the  mouth,  the  Nemer- 
teans  only,  the  most  hi<>hly  or«>ani/ed  class  of  the  Platvhel- 
minths,  possessin<,f  a  second  opening,  the  (nin.H. 

These  homologies  are,  however,  associated  with  a  com- 
plexity of  organization  unrepresented  in  the  Co'lenterates. 
The  Platyhelminths  all  present  a  tyj.ical  bilaterality  of  form, 
and  show  furthermore  a  well-marked  antero-posterior  as  \\v\l 
as,  in  most  cases,  a  dorso-ventral  dittenrntiation.  The  body  is 
usually  riatteued  and  more  or  l(>ss  vermiform,  whence  the  mune 
of  the  group,  and  is  adai)ted  to  a  creeping  habit,  certain  j)ara- 
Hitic  forms,  and  some  Nemerteans  which  live  buried  in  sand, 
being  the  only  forms  not  ])resenting  such  a  mode  of  life. 

The  greatest  contrast  to  what  occurs  in  the  C<elent(>rHte» 
however,  is  presented  by  the  development  of  compact  organs. 
The  nervous  system  is  no  longer  an  altogether  diffuse  tissue, 
scattered  in  a  thin  layer  throughout  the  body,  but  a  large 
uumber  of  ganglion-cells  are  aggivg.-ited  into  a  "compact  mass, 
the  brain,  embedded  in  the  mesochMin  j)arencliyma  near  tlie 
anterior  end  of  the  body,  and  fr.)m  this  there  pass  backwartis 
two  or  more  longitudinal  cords  of  nerve-libres  which  give  iA\ 
branches  extending  to  all  parts  of  the  body  and  forming  a 
network  below  the  basement-membrane  from  which  the  \iv.- 
rii)hera,l  muscles  deiiv(*  their  nerve-supply.  In  some  cases 
nerves  hav(>  been  observ(>d  to  pass  fn.in  this  network  throu'Mj 
the  basementmembraue  to  come  into  conuectiou  apparently 


TYPE  PLATYUELMINTUES. 


13» 


with  nerve-cells  \y\\i<^  between  the  inner  ends  of  the  ectoderm- 
cells  us  well  as  with  sensory  cells  reseniblinfr  in  general  form 
those  ulreudy  described  us  occurrinj,'  in  the  Cniduria.  It  nuist 
not  be  understood,  however,  that  the  gan<,'lion-cells  are  limited 
ill  their  <listribution  to  the  lower  layer  of  the  ectoderm  and 
the  brain  ;  on  the  other  hand,  they  are  scattered  along  the 
nerve-cords  which  arise  from  the  brain,  the  Platyhelminths 
] (resenting  in  the  structure  of  their  nervous  system  a  condi- 
tion intermediate  between  the  ditt'use  arrangement  of  the 
^■unglion  cells  ;ieen  in  the  Cnidariu  und  the  more  perfect  ag- 
gregution  occurring  iji  lilgher  types. 

An  excretory  system  of  branching  tubes  traversing  the 
mesoderm  parenchyma  and  opening  U)  the  exterior  is  also 
l)resent.  It  consists  usually  of  two  main  tubes,  nejjhridiu, 
from  which  numerous  branches  arise,  terjiiinatin-'-  in  blind 
fiuinel-like  extremities  (Fig.  70,  /')  lying  in  the  meshes  of  the 
parenchyma.  Euch  funnel  (Fig. 
78,  It)  is  closed  bv  a  singhi  cell 
(/(•),  from  which  there  ju-ojects 
into  the  tube  a  bundle  of  cilia 
(/),  and  which,  from  tht  '•('sem- 
blance of  the  motion  of  these  cilia 
to  a  Hame  flickering  in  the  wind,  is 
known  as  iijt<nnc-ccl(.  The  larger 
tid)es  are  lined  by  a  layer  of 
cells  which  seeiii,  in  certain  cases 
ill  least,  to  be  ciliated,  but  the 
smaller  branches  consist  of  a 
series    of    c.dls    succeeding    (,ne  ^';;;,,^*i~f  ""'T'  ^''■'''"   "^ 

,,  .  .         ,  ,  "ti;    AntKHk.U  PoUTioN    ,,K  THE 

.iMotlier  m  a  smgh;  row,  the  canal      H..nv  ok  riunaria  montana  iftfter 
running   through    the   centres   of    <'hichk(iifi. 
the  cells   and    being    thus    intra-        ^' ^  '""""'• 


oc  =  eye. 


'•"Inlar.  Th.^  tubes  throughout  the  entire  svstem  contain 
a  Huid  in  which  particles  resembling  guanin  in  their  behavior 
♦<•  ivagents  have  been  seen,  and  there  is  little  room  for  doubt 
I'ut  that  the  tnbe.s  have  an  excretory  function. 

Finally,  a  complicated  reproductive  apparatus  (see  Figs. 
^•'H-70)  is  present,  the  IMatyhelminths  being  for  the  moHt  ])art 
iH'iinaphrodite.     The    t.vstes  consist   of   from    two    to    nuiuy 


130 


INVERTEBRATE  MORPHOLOGY. 


globular  bodies  whose  ducts  unite  to  form  two  vasa  deferentia 
opening  to  the  exterior  through  a  muscular  intromitteut  organ, 
and  sometimes  dilating  to  form  reservoirs,  the  seminal  vesicles, 
ill  which  spermatozoa  may  be  stored  up  until  required  for 
fertilization,     The  female  apparatus  is  somewhat  more  com- 
plicated.    The  ovaries  are  usually  two  in  number  and  their 
products  pass  to  the  exterior  through  speci-1  tubes,  the  ovi- 
ducts, which  may  be  exceedingly  long  a  M-  the  terminal 
portion  dilated  to  form  a  uterus  in  whic';  ova  may  pass 
through  certain  stages  of  their  development.     Connected  with 
the  oviducts  there  is  usually  a  pouch-like  structure,  the  sani- 
nal  receptacle,  for  the  reception  of  spermatozoa,  and  further- 
more   they  may  receive    the  products  of   two   other  glands 
which  supply  the  yolk  and  the  shell  for  the  ova.     The  yolk- 
glands  are  in  some  cases  very  voluminous,  forming  what  is 
termed  the  vitellarium,  and  have  been  apparently  developed 
by  the  separation  of  a  portion  of  the  original  ovary,  their 
cells,  which  manufacture  the  yolk  material,  being  accordingly 
equivalent  to  germ-cells.     The  evidence  for  this  supposition 
is  derived  from  the  arrangement  found  in  some  Tiirhellaria 
and  will  be  pointed  out,  together  with  the  variations  which 
the  complex  of  organs  presents,  in  the  descriptions  of  the 
various  groups. 


I.  Class  Turbellaria. 

The  Turbellaria  derive  their  name  from  the  fact  that  the 
ectoderm  is  furnished  with  cilia,  Avhich  form  the  locomotor 
organs  of  the  animals,  whose  gliding  motion  over  the  sur- 
face of  the  objects  among  which  they  live  is  very  charac- 
teristic. The  majority  of  the  members  of  the  class  lead  a 
free  life,  some  in  fresh  and  some  in  salt  water,  and  some  even 
on  land,  creeping  about  on  the  under  surfaces  of  stones  or 
weeds.  A  few,  however,  are  parasitic  either  upon  the  outside 
of  the  bodies  of  their  hosts  {Bdellura)  or  in  a  few  cases  liviii-^ 
in  the  body-cavity  or  even  being  imbedded  in  the  tissues. 

In  addition  to  the  ordinary  ciliated  cells  the  ectoderm  con- 
tains numerous  sensory  as  well  as  gland  cells.  Hjiecial 
glands  secrete  in  most  uf  the  groups  peculiar  rod-like  bodies 


TYPE  PLATYIIELMINTHES. 


131; 


which  lie  scattered  about  iu  the  ectoderm  between  its  couiijo. 
neiit  cells  or  may  project  more  or  less  beyond  its  surface 
These  rhahdites,  as  they  are  termed,  are  produced  as  a  secre- 
tion by  cells  lying  usually  in  the  mesoderm  and  connected 
with  the  exterior  by  a  slender  neck  passing  through  the  base- 
ment-membrane, the  rhabdites  thus  making  their  way  to  the 
exterior.  The  rhabdite-cells  are  ectodermal,  their  position  in 
tlie  mesoderm  being  quite  secondary,  and  in  fact  in  one  group 
they  are  confined  to  the  ectodermal  layer.  The  function  and 
nature  of  the  rhabdites  have  been  variously  interpreted  some 
authors  considering  them  equivalent  to  the  Cnidarian  nemato- 
cysts,  but  It  seems  more  probable  that  they  are  the  condensed 
secretion  of  cells  which  originally  produced  a  mucous  sub- 
stance and  by  slowly  dissolving  in  water  produce  a  viscid 
shme  of  sufficient  tenacity  to  retain  organisms  coming  in  con- 
tact with  it. 

In  addition  to  these  structures  many  forms  possess  adhe- 
sive  cells,  columnar  cells  which  produce  a  strongly  adhesive 
secretion  which  is  poured  out  iu  drops  upon  the  free  ex- 
tremity of  the  cell,  recalling  in  this  respect  the  adhesive  cells 
of  the  Cteuophores.  These  cells  seem  to  be  of  use  mainly  in 
enabling  the  worms  to  adhere  to  the  surface  on  which  they 
are  creeping,  and  are  especially  developed  towards  the  hindeV 
end  of  the  body.  Another  organ  of  adhesion  in  the  form  of  a 
muscular  sucker,  situated  usually  about  the  middle  of  the 
ventral  surface,  is  present  in  certain  marine  Turbellaria,  but 
the  majority  of  the  members  of  the  group  lack  such  struc- 
tures. 

The  nervous  system  consists  of  a  brain  from  which  a  num- 
ber of  nerve-cords  arise,  varying  somewhat  in  their  arrau ere- 
nient  in  the  different  orders.  Sense-organs  of  one  kind  "or 
another  are  usually  present  in  addition  to  the  widely-distrib- 
uted sensory  cells  of  the  ectoderm.  A  large  number  of  forms 
possess  eyes,  which  in  s.uie  Polyclads  mav  be  exceediudv 
numerous,  and  usually  consist  of  a  patch  of  "pigment  lyin«  in 
he  mesoderm  and  upon  which  a  refractive  lens-like  structure 
lies.  In  a  few  cases,  as  in  Jlwmsfoma,  the  eye  is  simply  a  ijatch 
ot  pignicM.t  in  the  ectoderm  near  the  anterior  end  of  the  body 
An  otocyst,  consisting  of  a  spherical  vesicle  tilled  with  fluid 


C0 

I 


132 


INVERTEBHA TE  MOItPIIOLOG Y. 


^lul  coutaiiiiug  au  otolith  of  carbonate  of  lime,  is  present  in 
some  of  the  lower  Turbellaria,  as  Monotm,  and  rests  direct! v 
upou  the  surface  of  the  brain ;  these  structures  probably,  as 
in  the  Cnidaria,  are  sense-organs  of  equilibrium  rather  thai, 
of  audition.  In  the  Polyclads  tentacles  are  frequently  pros- 
ent,  sometimes  cai)able  of  being  retracted  and  serving  ^s 
organs  of  touch,  and  in  certain  llhabdoc(i>ls  there  is  a  ciliated 
depression  on  each  side  of  the  head  richly^  supplied  with 
nerves  forming  what  has  been  considered  an  olfactory  or-aii 


1.  Older  Accela. 

The  Accxila  form  a  group  of  lowly-organized  Turbellaria 
exclusively  marine  in  habitat  and  leading  an  active  and  free 
existence.     They  all  possess  a  mouth  (Fig.  71,  m)  situated  (,n 
the  ventral  surface  and  leading  into  a  short  pharynx,  though 
in  some  forms  this  may  be  absent;  but  beyond  this  there  ""is 
no    trace   of   a   digestive    tract,    the  food    passing   from    tlu> 
pharynx  into  the  parenchyma  [p),  where  it  is  digested.     Ow- 
ing to  the  lack  of  a  digestive  tract  these  forms  are  strictly 
tNvo-layered  (Fig.  m,A),  only  the  ectoderm  and  mes-endoderni 
being  represented,  and  consequently  are  exceedingly  interest- 
ing as  indicating  the  manner  in  which  the  ditlerentiation  Of 
the  triploblastic  condition  has  been  derived  from  the  dipio- 
blastic. 

The  nervous  system  has   been  described  in  Convohda  as 
consisting  of  a  bilobed  ganglion  surrounding  the  otocyst,  ami 
in  front  of  this  and  united  to  it  by  commissures  is  a  second 
pair  of  ganglia.     From  the  anterior  ganglia  there  arise  by  a 
common  stem  two  nerves  on  each  side  which  pass  backwards 
one  along  the  edge  of  the  btxly  and  the  other  a  little  internal 
to  It,  while  the  posterior  ganglionic  mass  gives  rise   to  two 
nerves  which  pass  backwards,  one  on  each  side  of  the  median 
line.     All  six  nerves  send  ott"  numerous  transverse  branches 
which  unite  to  form  with  the   nerve-cords  a  square-meshed 
network.     In  addition  to  the  single  otocvst  (Fig.  71,  of)  two 
pigment-spots  lying  in  the  ectoderm  and' representing  li.rht- 
percipient  organs  (e)  are  present,  as  well  as  a  ])ecnliar  refrac- 
tive highly-movable  organ,  lying  in  the  median  line  on  the 


T  YPE  PLA  TYlIELMINTima. 


133 


anterior  margin  of  the  body,  which  is  supposed  to  be  tactile 
lU  luuctioii. 

No  excretory  apparatus  has  as  yet  beeu  described  for  the 

Acuila,    but    a    reproductive    system 

with   some    iuterestiug   peculiarities 

occurs.     The  male  apjiaratus  consists 

of  numerous  spherical  testes  (/)  whose 

ducts    unite  to  two  vasa  deferentia, 

dilating   bek)\v  to  form  the   seminal 

vesicles  (y.v)  and  uniting  in  the  mus- 

cuhir  intromittent  organ.     The  female 

organ  is,  however,  relatively  simple, 
consisting  of  two  club-shaped  ovaries 
(oy)  whose  short  oviducts  open  almost 
directly  to  the  exterior  near  the  pos- 
terior end  of  the  body  by  a  pore  (^  9 ) 
common  to  both  male  and  female  ap- 
paratus. There  is  no  vitellarium,  no 
shell-gland,  no  seminal  receptacle, 
and  no  special  uterus,  a  state  of 
affairs  indicating  great  simplicity  of 
structure  compared  witli  what  is 
found  in  the  other  orders. 


2.  Order  AUoi.ocoela. 


The  members  of  this  order  are 
marine  with  the  single  exception  of 
Plmjiostoma  lemani,  which  is  found  in 
the  deep  waters  of  the  Swiss  lakes. 
They  present  a  distinct  advance  upon 
the  Acoela  m  that  a  well-deiined  diges- 
tive' tract  is  present  (Fig.  09,  n)^i\i& 

interval  between  it  and  the  peripheral  ^  ^  =  >ei>i<)diKiivo  oiitice. 
".usculature  being  completely  filled  up  by  the  usual  paren- 
chyma and  the  organs  in.bedded  in  it.  These  forms  are  then 
tnploblastic,  possessing  well-defined  ectoderm,  mesoderm,  and 
eiidoderm,  a  condition  found  m  all  tl.ie  higher  orders 

The  mouth  varies  somewhat  in   position,  Iving  either  near 


Fig.    71.— Diaoham   of    an 

Ac(KI,(»»:^^      Tl'KHELLAKTAN 
(uftf r  VON  Gbakk). 
e  =  i.'ye. 
til  =  mouth. 

Ot   =.    OtOCViit. 

ov  =  ovaiy. 

P  =  parenchyma. 
t  =  testis. 
V8  =  vcsicul.i  seminalis. 


I 

§ 

c 

I 

5 


134 


INVERTEBRATE  MORPHOLOGY. 


the  anterior  or  the  posterior  eud  of  the  body,  and  opens  into 
a  pharyngeal  pouch,  whose  walls  are  thickened  by  muscle-fibres 
in  such  a  way  as  to  form  a  somewhat  bulbous  mass  sharply 
marked  off  from  the  parenchyma  which  surrounds  it.  In 
Monotus,  however,  the  pharynx  is  more  developed,  projecting 
as  a  strong  circular  fold  into  the  pharyngeal  pouch  and  form*"- 
ing  what  is  termed  a  plicated  pharynx.  This  at  its  imier 
extremity  communicates  with  the  sac-like  intestine,  usually 
quite  simple  but  occasionally  somewhat  pouched,  and  ter- 
minating, as  in  all  the  Turbellaria,  blindly. 

The  nervous  system  consists  of  a  bilobed  ganglionic  brain- 
mass  from  which  pass  backwards  two  nerve-cords  Avhich  may 
{Monotus)  or  may  not  present  transverse  anastomosiu^^^ 
branches,  and  in  addition  a  number  of  smaller  branches  pass 
forward  to  be  distributed  to  the  anterior  end  of  the  body. 
Eyes,  consisting  of  pigment-spots  seated  upon  the  brain,  are 
frequently  present,  and  in  3Ionotus  an  otocyst  is  fouad,  while 
l^'teral  ciliated  depressions  on  each  side  of  the  head  occur  in 
Pla(jL''*oma. 

The  excretory  system  is  present,  but  presents  no  notable 
departures  from  the  typical  arrangement.  As  regards  the 
reproductive  organs,  the  testes  resemble  those  of  the  Acoelji, 
but  the  ovaries  are  comparatively  small  and  the  separate 
vitellaria  are  large  and  sometimes  branched,  opening  into  a 
cavity,  the  genital  atrium,  common  to  them,  the  oviducts 
and  the  intromittent  organ,  and  communicating  with  the  ex- 
terior by  a  single  median  pore  situated  near  the  posterior  end 
of  the  body.  In  a  few  forms  the  vitellaria  are  not  differen- 
tiated from  the  ovaries,  presenting  a  condition  similar  to  that 
found  in  the  Accela. 


3.  Order  Rhabdocoela. 

The  Rhabdocoela  are  found  both  in  fresh  and  salt  water  and 
are  usually  small.  They  possess  a  distinct  tubular  digestive 
tract  (Fig.  69,  C,  d)  without  lateral  pouches  or  branches,  but 
the  principal  characteristic  lies  in  the  presence  in  the  paren- 
chyma of  large  spaces  resembling  the  coelomic  cavities  of 
higher  typos,  a  feature  not  repeated  in  any  other  Turbellariiu 


TYPE  PLATYHELMTNTHE8.  135 

Tlio  moutli  is  situated  at  various  regions  of  the  body  iu 
diftereut  forni.s,  being  anterior  in  Microstorm,  while  in  Me^o- 
stoma  (lig.  72)  it  is  situated  at  the  middle  of  the  ventral  sur- 
lace.     The  walls  of  the   pharyn-  — 

geal  pouch  {ph)  n,ay  be  quite 
simple,  as  in  the  Acrela  which 
possess  a  pharynx,  or  may  pre- 
sent a  muscular  thickening  form- 
iiJg  a  bulbous  pharynx,  but  no 
further  complexity  occurs,  aJ- 
tliough  in  certain  forms,  such  as 
Prorhyiiohus,  the  pharynx  is  capa- 
ble of  being  protruded  from  the 
mouth,  acting  probably  as  j, 
delicate  tactile  organ. 

The  nervous  system  (w)  is 
essentially  similar  to  that  of  the 
Alloiocoela;  two  or  four  eyes  {oc) 
frequently  occur,  though  otocysts 
Jiie  wanting,  while  the  ciliated 
depressions  on  the  side  of  the 
head  supposed  co  be  olfactory  in 
fuucHon  occur  in  Microstoma  and 
riorhynchus  and  allied  forms. 

The  excretory  system  consists  ^^ 

occasionally  of   a   single   nephri    ^"*-'''^~^  ^«abdoc<elousTur. 
dium    witli    numerous   bro.nches      !^^.^^«'^^'- ^^*^*''''««  ^^'^^'f*- 
which    open   near    the   posterior 
end  of  the  body,  but  more  usually 
two  main  tubes  are  present  open- 
in-  near  the  middle  of  the  b  )dy 
either  directly  to  the  exterior  or 
into  the  pharyngeal  pouch  {Meso- 
stcnia),  though  in  some  cases  they 
unite  near  the  posterior  end  of  the 
body  into  a  single    tube   which        ^«  -  ,u,.-g.Hnc. 


J   »] 


dmn  (after  von  Graff). 

at  =  atrium. 
atg  =  iitrial  gland. 
d  =  intestine. 

n  =  biidu. 

oc  =  eye. 

ov  -  ovary. 

p  =  penis. 
M  =  pliarynx. 

sr  =  leceptaciilum  seminis. 
t  =  testis. 

»i  =  yolk-gland. 


136 


INVERT EBHA TE  MOliPlIOLOG ¥. 


uniformly  two  simple  club-shaped  bodies  uuiting  below  to 
form  a  common  seminal  vesicle.  The  female  apparatus  may 
consist  of  a  single  ovary  (ov)  combined  with  a  vitellarium  oV 
of  two  such  structures,  but  usually  there  is  a  separation  of  the 
vitellarium  (vi).  In  the  more  complicated  cases  there  is  but 
a  single  small  ovary  opening  almost  directly  into  the  genit.il 
atrium,  which  recei^  -s  also  in  addition  to  the  intromitteut 
organ  the  ducts  of  t  .=  two  vitellaria.  Its  walls  are  furtlier- 
more  pouched  out  into  a  seminal  receptacle  and  a  sac-like 
CLvity  which  serves  as  a  uterus,  while  a  peculiar  muscular 
sac,  lined  by  a  strong  cuticle,  the  bursa  copulatrix,  serves  f(n- 
the  reception  of  the  intromittent  organ  during  copulation. 
As  stated,  however,  numerous  variations  from  such  a  conditiou 
occur,  and  it  is  not  possible  to  describe  any  one  arrange- 
ment characteristic  of  all  the  Khabdocoils. 


4.  Order  Tricladea. 

The  Triclads  constitute  a  group  of  forms  with  very  definite 
structural  peculiarities,  occurring  principally  in  fresh  water 
(Planaria,  Dendroccelum,  Phagocata),  though  a  few  forms  are 
terrestrial    {Bipalium),   and   a   still  smaller   number   marine 
{Gunda,  Bdelloura).     As  a  rule  they  are  elongated  in  form 
one  of  the  terrestrial  species  reaching  a  leugth  of  2  cm    ami 
are  for  the  most  part  free-living,  though  Bdelloura  and  ^yncw- 
lidtum  are  ectoparasites  of  the  King-crab  (Linudus).      Tlie 
mouth  is  situated  in  all  cases  behind  the  middle  of  the  body 
and  leads  into  a  somewhat  capacious  pharvngeal  pouch  (Figs 
69,  IJ,  and  73,  ph)  in  which  lies  a  muscular  cvlindrical  pharynx 
capable  of  protrusion  from  the  mouth-opening.     The  di-res- 
tive  tract   at   the  base  of   the   pharynx   divides  into   throe 
branches,  one  of  which  passes  forward  in  the  median  line 
giving  off  simple  or  branched  diverticula  on  both  sides,  whi'e 
the  other  two  pass  backwards  on  either  side  of  the  pharyngenl 
pouch,  giving  off  diverticula  only  from  the  outer  side."    The 
intestinal  branches,  whose  number  has  suggested  the  name  of 
the  order,  and  their  diverticula  are  imbedded  in  a  compact 
parenchyma,  no  well-marked  coelomic  spaces  being  present 


TYPE  PLATnitiJLMINTHES.  137 

The  nervous  system  consists  of  a  bilobed  braia  lying  in 
the  anterior  part  of  the  body  and  ^ 

from  which  two  nerve-cords  i)ass 
biickwards,  united  at  intervals  by 
cross-commissures  and  giving  otf 
«'H  their  outer  sides  branches 
wliich  anastomose  with  one  an- 
other,  forming  a  network. 

Ill  Gunda  segmentata  tlie  transverse 
cotiimissures  agree  in  number  and  ar- 
nm-c'iuont  vvitli  the  lateral  branches  on 
tlic  one  hand  and  with  the  diverticula  of 
til"  intestine  on  the  other,  the  arrange- 
ment of  the  two  systems  producing  an 
appeanince  of  nietanierization  which  is 
most  striking,  especially  as  it  affects  as 
well  the  excretory  and  reproductive  sys- 
tems.    In  this   form   an    indication  is 
afforded  of    the  maimer  in   which  the 
more  pronounced  and  typical  metameri- 
ziition  of  the  higher  types  has  been  pro- 
duced by  the   more  or  less  comi)leted 
multiplication  of    the  organs    and   the 
integration  of  the  parts  so  formed  into 
a  metaraere  (see  p.  43), 

Eyes  are  usually  present,  fre- 
queutly  provided  with  lenses,  and, 
though   usually  two   in   number,  ^^  ^ 

may  be  veiy  numerous  and  situ- Fro.  73.-A  Triclab  Turbkilarx- 
ateti  along  the  margin  of  the  body,     ^n,  Sf/ncwimum  peiiucidun  (after 
Nootocysts  occur,  and  the  sides     ""■""'"^ 
of  the  anterior  end  of  the  body 
file  in  some  forms  produced  into 
more  or  less  elongated  processes 
^vhich    may    possibly  be    mainly 
sensory  in  function,  while  behind 
the.u  are  areas  of  strongly  ciliated 
cells  richly  supplied  with  nerves 
and    presumably    corresponding 
with  the  ciliated  depressions  oc- 


Whekleb). 

ex  =  excretory  S3'slem. 
ff  =  accessory  glund. 
ggl  =  vaginal  glands. 
n  =  nervous  system. 
od   =  oviduct. 
ov  =  ovaiy. 

p  =  reproductive  orifice. 
P^t  =  pharynx. 

t  =  testis. 

u  =  uterus. 
vd  =  vtm  deferens. 

■VI  =  yolk-glriiiu. 


i 

5 


c»n-.ug  m  tLe  same  region  i„  the  Alloiocoela  and  Bbabdoccela. 


138 


INVEIiTKBRA  TE  MOliPIIOrAlG  Y. 


The  excretory  system  diliers  from  that  of  the  lower  orders 
iu  that  the  two  h>ngitudiiiHl  iiephridia  open  on  tlio  iloraal  sur- 
face of  the  btxly  by  numerous  pores,  which  iu  Gimda  corre- 
spond  in  number  with  tlie  iutestinni  diverticuhi  and  nerv(!- 
eommissures.  The  re})roduc'tive  apparatus  consists  of  nu- 
merous testes  (Fig.  7;5,  /),  as  iu  the  Aco'la  (arranged  uK^tameii- 
cally  in  (iinxfa),  whose  ibiets  unit(>  to  vasa  defereutia  (r<l) 
uniting  in  the  musouhir  iutromittent  organ  wliich  })rojet'ts  iii((» 
the  genital  atrium.  Two  small  ovaries  {or)  occur  iu  the  ante- 
rior ei\d  of  the  body,  their  largo  oviducts  passing  backwards  to 
unite  in  a  muscular  hurm  vopnhfri.v,  and  receiving  at  inter- 
vals the  secretion  of  numerous  lateral  divi^rticula  which  con- 
stitute the  vitellarium  [n').  A  j)ouch-like  diverticulum  of  the 
atrium  serves  as  a  uterus,  aud  the  single  median  oriHce  (p)  of 
the  atrium  lies  near  the  posterior  eud  of  the  body  behind  the 
mouth-opeuiug. 


5.  Order  Polycladea. 

The  Polyclada  are  exclusively  marine  aud  assume  various 
forms,  some  being  (piite  elongated  while  others  are  tlat  l(>jit'- 
like  expansions.     Compared  with  the  members  of  the  other 
orders  they  may  be  said  to  be  as  a  rule  large,  though  few 
reach  the  length  which  has  been   mentioned  for  sonu'  IuihI 
Trichuls.     The  mouth  varies  greatly   in   position,  as   in  the 
Khabdoc(els,  and  opens   into  a  spacious   pharyngeal   poueli 
containing  a   plicated   ])harynx  (Fig.  T.'l,  p/i).     The   intestine 
consists  of  a  ctMitral  cavity,  into  which  the  pharynx  ojiens  ;it 
its  iuutu-  end  and  from  which  numiM-ous  braiu-hes  (hence  tlio 
name  of  the  order)  pass  olV  into  the  compact  parenchvni.i, 
where  they  branch  and  may  anastomose  with  one  another  to 
f<n-m  a  network.     The  nervous  system  presents  a  sonuMvh.it 
similar  condition,  the  bilobed  brain  {re),  usually  situated  near 
the  anterior  eud  of  the  botly,  giving  oil' a  number,  usually  six, 
of  nerve-cords  which  become  lost  in  a  wide-meshed  network 
ramifying  through  the  body-tissues.     Eyes  are  usually  pres- 
ent, freiiuently  in  enormous  numbers,  aud  furthermore  iu  many 
forms  (  J*lit))i>rri'ii)  tentacles  !iris<»  from  thf^  ihiry,'!}  t(urfact-  =  r 
elue  from  the  margin  near  the  anterior  eud  of  the  bodv.     As 


TYPE  PLATYIIELMINTUES. 


189 


Vd 


in  the  Triclads  otocyHts  are  wuutiug,  uor  have  ciliated  lateral 

dei)roHHious  been  described  as  occurring  in  the  order. 
Little  is  kuowu  couceruiug  the 

excretory  system.     The  reproduc- 
tive   system    diflers   from    that   of 

tlie  other  orders  iu  that  the  male 

nud    the    female    ap])aratu.s   each 

possess  a  separate  opening  ( i*  imd 

? ),  there  being  no  genital  atrium 

common  to  both,     lioth  apertures 

he  behind  the  mouth-o])ening,  near 

tiie    })osterit)r    end    of    the    body, 

the    male    ap])aratus    opening   an- 
teriorly to  the  female.     The  former 
is  simihir  in  structure  to  what  has 
been  described    for   the    Triclads. 
The    female    ai){)aratus    possesses 
no  vitellarium,  and  the  ovaries  {ov) 
are  very  numerous,  lying   in   the  ^^ 
lateral    parts   of    the    body,   their 
various  ducts  uniting  to  form  wide 
canals  which    serve    as    uteri   {nt). 
These  open  into  a  single  tube,  the 
■rtu/ina,  which  receives  the  secretion 
of  the  numerous  glands  (sg)  which 
form  the  shell-gland. 

In  some  forms  there  is  situated  ^^^  «.      .  ,, 
about  the    muldle    of   the   ventral      .11.,*^,      7    ,    ,  ,  ■  ■■ 

surface  of  the  body  a  muscular  ofier  lanu). 
sucker  which  serves  as  an  organ  of  "^  ""  nccfssoiy  frlund 
julhiisiou.  Hince  the  presence  or 
absence  of  this  organ  is  in  eitiior 
case  associated  with  the  occurrence 
of  other  important  structural  pecu- 
liariti(>H,  the  order  has  been  divided 
into   two    sul)orders  —  the  (oltflnt, 

provided  with  a  suclier  ( /'////.yrOH*.  ($  .  2  =  "mlt'iiml  fi'iimlcoiiiices. 
zoo,,,  Eimjhpta),  and  the  Amfylm,  m  which  it  is  absent 
{Planocera,  Leptoplomt). 


ce  =  cciehrul  gaiigHou. 

t>»  =  oviiry. 

l>h  =  plmiyiix. 

sg  =  slu'llgluud. 

te  ~  testis. 

itt  =  titerus. 

vd  --  VHH  (leferons. 

vs  -  vt'siculii  .siMiiiniilis. 


140 


INVERTEBRATE  MORPHOLOOT. 


Reproduction  of  the  Turhellaria.~^on.mxnii\  reproductiou 
is  not  characteristic  of  the  x'urbellaria,  though  it  occurs  iu  cer- 
tain Bhabdocoels.     Iu  Jlicrostoma  a  transverse  partition,  con- 
sisting of    two   closely-applied    laniellrt%   forms,    extending 
from  the  outer  wall  of  the  body  to  the  wall  of  the  digestive 
tract,  Aviiich  it  constricts  slightly  without  dividing.     Later  a 
constriction  of   the  outer  surface  of  the  body  appears,  the 
two  lamella}  of  the  partition  separate  slightly,  and  the  indi- 
vidual lying  behind  the  partition  develops  a  new  mouth  and 
pharyux  and  a  new  brain,  so  that  it  resembles  exactly  the 
anterior  individual  with  which  it  is  directly  connected  by  the 
uninterrupted   digestive   tract.     Before   these    processes  are 
complete,  however,  they  are  repeated  in  each  of  the  two  indi- 
viduals, so  that  a  chain  of  four  imperfectly  separated  individ- 
uals results,  and  by  further  repetitions  of  the  process  chains 
of   8,   16,  or  32    individuals  may  arise,  each  provided  with 
mouth,  pharynx,  and  brain,  the  anterior  individual  possessing 
the  original   structures,  and  all  connected  by  the  digef,tive 
canal  which  runs  uninterruptedly  through  the  entire  chain 
(see  Fig.  28).     Eventually  the  various   individuals  separate 
from  one  anotlier  and  become  sexually  mature. 

The  sexual  method,  however,  plays  a  much  more  important 
part  in  the  life-histories  of  the  Turbellaria.  The  development 
of  the  three  lower  groups  has  not  as  yet  been  as  thorouglily 
investigated  as  is  desi.-able,  but  the  i)henomena  which  occur 
in  the  Triclads,  find  especially  in  the  Polychids,  have  been  fol 
lowed.  The  Triclads  deposit  their  ova  iu  chitinous  cocoons, 
which  c  mtain,  besides  the  ova  pro])er,  large  numbers  of 
am(id)oid  cells,  originating  in  the  vitellarium-pouches  of  t\u\ 
parent,  and  serving  as  food  for  the  young  embryo.  In  asso- 
ciation with  this  condition  of  affairs  many  peculiarities  of 
segmentation  and  growth  occur  in  the  Triclad  embryos,  all  of 
which  must  bo  considered  as  secondary  adai)tations. 

In  the  Polydads,  however,  a  more  primitive  state  of  alia i is 
occurs,  the  food-yolk  being  incor])orated  with  tlie  protophism 
oi  the  ovum,  a  more  or  loss  distinct  irregular  segmentatidii 
resulting  from  its  telolecithal  arrangement  (p.  63).  'J'Ik^ 
dii>l:>})l;iHtic  eouditiou  arises  by  an  invagination  either  of  tlie 
embolic  or  epibolic  type,  but  at  an  ejirly  period  of  the  Hegnien 


TYPE  PLATYHELMINTHEa. 


141 


tfition  the  cells  which  are  to  form  the  mesoderm  are  separated 
off  from  those  from  which  the  ectoderm  and  eiidoderm  are  to 
be  derived,  so  that  even  before  the  iuvagination  all  the  three 
lajei-s  are  represented.     This,  however,  is  to  be  regarded  as  a 
juecocious  segregation  of  the  germ-layers,  and  even  within  the 
limits  of  the  few  forms  whose  embryology  is  known  consider- 
iible  variations  in  the  time  and  manner  of  the  diflferentiation 
of  the  mesoderm  occur.     The  result  of  the  invagination  is  in 
some  cases  a  solid,  bilaterally  symmetrical,  ciliated  embryo 
consisting  of  a  layer  of  ectoderm  enclosing  a  central  mass  of 
eudoderm  and  mesoderm,  in  tiie  interior  of  which  a  cavity  ap- 
pears surrounded  by  the  eudoderm.    A  depression  appears  on 
the  ventral  surface,  which,  deepening,  finally  unites  with  the 
cuteron  and  forms  the  pharyngeal  pouch,  and  gradually  the 
characters  of  the  adult  are  assumed. 

In  some  forms  whose  ova  are  jirovided  with  comparatively 
little  yolk  the  embryo  leads  from  an  early  period  a  free-swim- 
iiiiiig    existence,   and    in  accordance  with  this  a  specialized 

form  has  been  acquired  and  a  slight  metamorphosis  is  neces- 

sary  for  the  conversion  of  this  Inroa  into  the  adult  ccmdition. 

In  Sfi/hchiift  the    embryo  develops   into    what   is  known  as 
docftes  larva,  a  bilateral  ciliated  structure  with  an  anterior 

and  posterior  tuft  of  strong  se».sory  hairs,  while  fronj  the  ven- 

tral   surface   on    either  side    of  the    mouth 

tlicre  hang  down  two  ciliated  ear-like  lobes 

or  lappets.     In  another  form   {Thymmzmw) 

these  ]ai)pets    are    much    more    developed, 

])assing  round  to  the  dorsal  surface  of  the 

body,  and   their  edges  are  drawn  out  into 

four  or   eight  lobes,  one   of  which    lies    in 

frimt   of   the    nnrnth   and    another   on  the 

dorsal  surface,  the  other  two  or  six  lying 

at  the  sides  of  the  body  and  being  arranged 

symmetrically   on   either   side.      It   seems  p,o.    7r,.-LAuvA   op 

probable  that  this  larva,  known  as  MilVcr's     ni/sanoJoi,,    Mm- 

hirra  (Fig.  75),  may  be  traced  back  to  a  con-     '•"■'»     iMyvn    («fter 

dition    such   as   that  described   in  (loette's     '"""'^' 

larva,  the  two  lapjiets  of  that  form  having  united   in  front  of 

the  mouth,  while  their  lines  of  attachment  have  become  more 


142 


INVERTEBRATE  MORPHOLOGY. 


i ' 


and  more  oblique  until  wLat  were  ori^riually  the  posterior 
edges  of  the  lappets  meet  on  the  dorsal  surface.  The  edj^es 
of  the  lobes  of  the  lappets  are  fringed  with  long  cilia,  aLd 
consequently  a  lobed  prseoral  baud  of  cilia  is  produced. 
These  larvee  pass  into  the  adult  form  by  gradually  becoming 
more  and  more  flattened  dorsoventrall/,  the  ciliated  lappets 
or  lobes  at  the  same  time  growing  smaller  and  smaller  until 
they  finally  disappear. 

Relatiomhips  of  the  Turbellaria.—A  relationship  of  the  Turbeliaria 
especially  of  the  Polyclads,  with  (he  Ctenophores  has  l)een  advocated 
within  recent  years,  and  through  this  relationship  genetic  affinities  with 
the  Cnidaria  have  been  sought.  The  question  of  the  affinities  of  the  Cteno- 
phores has  already  been  discussed,  and  it  has  been  pointed  out  that  it  is 
probable  that,  instead  of  being  a  connecting  link  between  the  Cnidaria  and 
the  Turbeliaria,  they  are  rather  highly  modified  Turbeliaria  adapted  to  a 
pelagic  life.  In  this  sense  the  idea  of  a  genetic  affinity  between  the  Turbel- 
iaria and  Ctenophores  may  be  correct,  though  it  seems  i)robable  that  the 
Polyclad  affinity  should  be  given  up  and  the  relationship  sought  for  among 
AUoiocoelan  forms. 

The  Ctenophore-Polyclad  theory  necessarily  viewed  tiie  Polyclads  as  tlie 
most  primitive  Turbeliaria,  and  came  into  contact  in  this  way  with  the 
more  simple  organization  of  the  Acoela,  Alloiomla,  and  Rhabdocvela  a 
difficulty  which  was  avoided  by  assuming  that  these  were  degenerate 
groups  derived  from  Polycladan  ancestors.  No  good  grounds  for  such  an 
assumption  exist  however,  nothing  in  the  mode  of  life  suggesting  a  cause 
for  degeneration  ;  and  until  embryological  evidence  of  degeneration  is 
obtained,  it  is  preferable  to  consider  their  simplicity  primitive. 

This  latter  view  is  strengtiiened  if  it  In  rmonizes  rtith  a  probable  phy- 
logeny.     It  has  already  been  pointed  out  that  the  solid  embryo  or  stermla 
is  to  be  recognized  as  an  ancestral  form  of  the  Cnidaria.     With  .such  an 
ancestral  form  the  .\ca>la  show  affinitii-s  in  the  absence  of  a  differentiation 
of  the  central  mass  into  well-(l(«finod  endoderm  and  mesoderm.     The  local- 
ization of  a  definite  region  for  the  ingestion  of  nutrition  would  lead  to  the 
formation  of  a  mouth  in  the  Sterrula,  ju.st  as  it  has  done  in  the  FlmielUita. 
The  differentiation  of  mu.scle-fibres  from  the  mesendodermal  cells  would 
naturally  follow  the  assumption  of  a  creeping  hal)it,  so  that  it  is  only  tlic 
l)ossession  of  a  definite  nervou^  system  imbedded  in  the  mcsoghea  (in  which 
ti.s3ue,  however,  Cnidarian  characteristics  are  yet  discernible,  as  already 
pointed  out)  and  the  occurrence  of  a  com])lieated  reproductive  apparatin 
that  render  a  eljse  comparison  with  the  Sterrida  difficult  ;  but  (jven  tlir 
«xplamition  of  the  presence  of  these  .structures  makes  fewer  demands  upon 
our  ideas  of  developmental  possibilities  than  does  the  a.s8umption  that  the 
Ai-ii'la  owe  their  peculiarities  to  deg(Mieration. 

Upon  this  view  of  the  phylogeny  the  AvwUx  are  united  with  the  Co'lcii 


TYPE  PLATYHELMINTHE8. 


143 


era  only  through  the  Sterrula  ancestor  common  to  both,  or  more  probably 
hrough  an  ancestor  in  which  the  mouth  had  developed,  as  well  as  a  slight 
differentiation  of  muscle-flbres,  but  in  which  no  hollowing  out  of  an  entemn 
had  yet  occurred.  This  appearing  in  a  primitive  acoelan  form  gave  rise  to 
xh^  Allmoccela  from  which  two  divergent  lines  of  descent  arose,  one  leadin-^ 
to  tiie  Rhabdocoels  and  the  other  to  the  Triclads  and  Polyclads 

If  this  be  the  true  phylogeny  of  the  class,  some  evidence  of  it  ouglit  to 
be  found  in  the  embryological  history  of  some  of  the  liigher  members  of 
the  group  in  accordance  with  what  is  termed  the  Biogenetic  law,  which  is 
to  the  effect  that  an  individual  in  its  development  recapitulates  more  or 
less  accurately  its  phylogenetic  development,  or,  to  put  it  more  briefly  the 
ontogeny  is  a  recapitulation  of  the  j^hylogeny.  Secondary  modifications 
especially  in  the  form  of  the  abbreviation  or  omission  of  certain  sta-es' 
may  intervene  in  the  individual  development,  f.)rming  what  are  termed 
cenogenetic  modifications,  but  notwithstanding  exceptions  produced  in  this 
way  the  law  is  of  general  application. 

In  8tylochas  the  young  larva  is  a  solid  body  without  any  enteron  and 
represents,  therefore,  an  Acoelan  stage  of  development ;  later  the  central 
mass  becomes  hollowed  out  to  form  an  enteron  whose  walls  are  not  at  first 
clearly  marked  off  from  the  surrounding  parenchyma,  and  a  representa- 
tion of  the  Alloiocffilan  condition  results,  from  which  the  Polyclad  condi 
tion  gradually  develops.     Consequently  in    mylochus  the  ontogeny  indi- 
cates a  primitive  nature  for  the  Actrla,  and  agrees  with  the  phylogenv 
which  has  been  outlined  above.     It  must  be  recognized,  however  that  ail 
reconstructions  of  the  phylogeny  of  the  Turbellaiia  and  all  views  as  to 
tlieir  afiinities  to  the  Cnidaria  must  Ijo  accepted  with  much  reservation 
until  the  muclMiecded  facts  as  to  the  developmental  history  of  the  Acala 
and  Alloiocoda  are  available. 


11.  Class  Tkematoda. 

The  Trematodes  or  Fluke-woniis  are  throughout  parasitic 
Snckers  are  preseut  in  all,  consisting  of  cup-like  depressions 
whose  walls  are  richly  supplied  with  niuscle-eells,  by  the 
i'ontraction  of  which  a  vacuum  is  formed,  and  in  many  forms, 
in  udditiou  to  these,  chitiuous  hooks  occur.  The  suckers  vary 
111  number  from  one  {MomsUymnm)  or  two  {DiHtomnm,  Fig.  76) 
to  several  {Pohjstomnm\  and  at  the  bottom  of  one  situated  at 
the  anterior  extremity  of  the  body  is  the  mouth-opening.  This 
l»"ii(ls  into  a  tubular  o>sophagns  whose  walls  are  thickened 
ix'ar  Its  anterior  end  to  form  a  muscular  phnn/iHf,'„l  hnJh  which 
functions  HH  ..,  pump  for  the  ingestion  of  the  nutritive  fluids  of 
the  host.     At  its  posterior  extremity  the  u-sophagus  branches 


144 


INVERTEBRA TE  MORPHOLOO  T. 


into  two  limbs  wbicli  are  continued  backwards,  in  some  cases 
giving  off  secondary  branches,  to  near  the  posterior  end  of 

the  body,  where  they  either  end  blindly 
or  unite  together  in  the  middle  line 
(Polystomum)  to  form  a  loop. 

The  body  is  covered  by  a  distinct 
cuticle  secreted  by  the  ectodermal  celJK, 
which  in  the  adult  may  undergo  a  con- 
siderable amount  of  degeneration,  or 
probably  in  some  cases  the  cuticle  is 
formed  in  part  by  the  transformation 
into  chitin  of  the  ectoderm.   Spiny  ele- 
vations of  the  cuticle  are  present  in 
many  forms,  and  the  large  chitinous 
hooks  which  occur  in  many  ectopara- 
sitic    forms   are  but  further  develop- 
ments of  these  structures.      Below  the 
ectoderm  lies  the  usually  thin   base- 
ment -  membrane,  below  which   again 
lie    the    circular  and  longitudinal  pe- 
Fw.  7Q.-i)i.tom,nn   cyg.     ripheral   muscle-sheets,   and    between 

HOe«^«  (from  a  (IrawitiL'  l)y       ,1         •     ,       ,.  1    ,,  ,         . 

the  intestine  and  these  muscles  is  the 
parenchyma  traversed  by  dorsoventral 
muscle  bundles  and  ha\  iiig  imbedded 
in  it  the  re])r()ductive  and  other  organs 
of  the  body. 

The  nervous  system  (Fig.  77)  con- 
sists of  a  transversely  elongated  gan- 
glion lying  dorsal  to  the  (esopluigus— 
usually  between  the  bottom  of  tln' 
ant(>rior  sucker  and  the  i)haryng»'iil 
bulb.  The  ganglion  is  somewhat  swollen  at  each  extremity, 
indicating  its  origin  by  the  approximation  of  two  ganglionic 
masses,  and  from  these  thickenings  nerves  arise  which  \y,\M 
both  forward  and  backward.  The  anterior  nerves  are  shoit 
and  slender,  and  supply  the  musculature  of  the  anterior 
sucker  and  the  sides  of  the  anterior  end  of  the  body,  whilf 
the  })osterior  nerves  are  much  sti'onger  and  longer  and  varv 
from  two  to  six  in  number  ;  in  the  latter  case  four  run  aloni^ 


C  Lan(!Knhkcki. 

as  =  iiiitcrioi'  sucker 

il  =  iiiU'stine. 
ov  =  ovary 

p  =  reproductive  orilico. 
ph  =  iiliiiryngoal  bulb. 
pe  —  cirrus. 
fe  =  testis. 
u(  =  uterus. 
vi  =  yolk-giand. 
va  =  veutral  sucker 


TYPE  PLATYHELMINTUES. 


145 


the  ventral  surface  of  the  body,  two  on  each  side  of  the  mid- 
dle line,  the  other  two  having  a  more  dorsal  position,  while 
when  only  two  are  present  they  correspond  to  the  two  more 
median  ventral    nerves  of  this 
arrangement.    Sense-organs  are 
but  feebly  developed  as  a  rule, 
especially  among  the  endopar- 
asitic  forms,  but  in  some  ecto- 
parasites eyes  are  present  con- 
sisting usually  of  four  spots  of 
})igment  seated  upon  the  brain- 
ganglion  and  sometimes  provid- 
ed with  a  lens-like  structure. 


Fid.  77.— Nehvous  System  of  Tke- 
MATOUE,  Triitomum  molui  (after 
Lanu). 


Fig.  78.— Excketouv  System 
OF    TiJEMATouE,    Distomum 
divergens  (after  Fraipont). 
A,  euiiie  system;    B,  terminal 

fuuuels. 
/  =  fuuuel. 
Jl  —  flume  of  ciliii. 
n  ~  muiii  iruuk. 
ph  =  pburyngeal  bulb. 
s  =  anterior  sucker. 
tc  =  termiuiil  cell. 
vs  =  ventral  sucker. 
vt  —  coutractile  vesicle. 


The  excretory  apparatus  (Fig.  78)  consists,  as  is  usual  in 
the  Platyhelminths,  t)f  two  longitudinal,  more  or  less  irregu- 
larly twisted  tubes  {n)  from  which  arise  the  funnel-bearing 
l)runches  (/).  A  peculiarity  of  the  Trematodes  is,  however, 
the  union  of  the  two  longitudiual  tubes  in  a  terminal  vesicle 
[vt)  which  opens  to  the  exterior  at  the  hinder  end  of  the  body 
by  a  single  pore. 

The  reproductive  system  is  exceedingly  complicated.though 
essentially  similar  to  that  of  the  higher  Turbellaria.     It  opens 


146 


INVERTEBRATE  MORPHOLOGY. 


to  the  exterior  by  two  pores  lying  close  together  on  the  ventral 
surface  rather   nearer  the   anterior  than  the  posterior  end. 
The  male  apparatus  consists  in  the  Polystomecv  of  numerous 
closely-aggregated  testes,  or  else,  as  in  the  Distomece  (Fig.  76), 
of  only  two  situated  in  the  posterior  half  of  the  body ;  the 
ducts  from  the  testes  pass  forwards  towards  the  genital  pore, 
near  which  they  unite    to   form    a   sac-like  seminal  vesicle,' 
from  whose  anterior  end  the  single  vas  deferens  is  continued 
on  towards  the  pore,  passing  in  the  latter  part  of  its  course 
through  a  muscular  protrusible  intromittent  organ,  the  cirrus. 
The   ovary  is   single,  and  its  duct  shortly  after  leaving  it 
receives  the  ducts  coming  from  two  yolk-glands  situated  one 
on  either  side  of  the  body,  and  is  surrounded  at  about  the 
same  region  oy  a  shell-gland,  consisting  of  a  number  of  uni- 
cellular glands  arranged  in  a  radiating  manner  around  the 
oviduct.     Beyond  its   union   with   these   ducts   the   oviduct 
either  runs   almost  directly  to   the  genital  atrium,  opening 
into  it  in  close  proximity  to  the  cirrus,  or  else  pursues  a 
winding  contorted  course  through  the  parenchyma  and  serves 
as  a  litems  or  ooti/p,  within  which  the  ova  undergo  a  portion 
of  their  development. 

From  the  oviduct  in  the  region  where  the  duets  from  the  vitellaria  and 
shell-glaud  open  into  it  one  or  more  canals  may  arise  whose  significance  is  to 
a  certain  extent  problematical.  In  the  Distomcas  one  such  canal  occurs,  and 
when  a  seminal  receptacle  is  present  it  stands  in  more  or  less  close  relations 
to  this  canal,  known  as  Laurer's  canal,  which,  after  a  short  course,  opens  to 
the  exterior  on  the  dorsal  surface  of  the  body.  In  some  Pblystomea  two 
canals  arise  from  the  yolk-ducts  and  pass  forwards  parallel  to  the  uterus 
to  open  by  a  number  of  pores  situated  on  the  margin  of  tiie  body.  Those 
canals  liave  been  termed  the  vagina,  and  in  some  forms  are  represented  l.y 
a  single  canal.  In  addition  to  the  vagina,  however,  another  canal  is  pres- 
ent which  has  been  shown  m  PoJystnminn  awl  Sphymnurato  o\^(in  into 
the  digestive  tract,  and  has  been  homologized  with  Laurer's  canal  of  the 
Distomeae. 

It  seems  pretty  certain  tiiat  the  vagina  of  the  Polystomese  functions  in 
copulation,  the  genital  orifice  of  one  Polystomuvi  having  been  observed  to 
come  into  contact  with  the  vaginal  openings  of  the  other  during  that  act. 
But  the  Laurer  canals  do  not  seem  to  have  any  such  function,  and  it  hiis 
been  suggested  that  they  may  serve  for  the  removal  of  surplus  yolk- 
material  produced  in  aceordancu'  with,  the  favorable  nonditions  for  nutri- 
tion offered  by  the  parasitic  mode  of  existence  of  the  Trematodc^s. 


TYPE  PLATYUELMINTHE8. 


147 


Two  orders  may  be  recognized  as  occurring  in  the  Tre- 
matoda. 

1.  Order  PolystomesB. 

The  PolystomesB  are  for  the  most  part  ectoparasites  and 
present  fewer  signs  of  degeneration  than  do  the  endopara- 
sitic  members  of  the  class.  The  apparatus  for  adhering  to 
their  hosts  is  usually  strongly  developed,  several  suckers 
usually  being  present,  as,  for  instance,  three  in  Tristomum 
and  seven  in  Polystomum  integerrimum  (the  latter  parasitic  in 
the  urinary  bladder  of  the  Frog),  and  in  addition  a  number  of 
chitinous  hooks  may  occur,  as  in  Gyrodadylus  and  Sphyranura 
(the  latter  parasitic  on  the  skin  of  3Ienobranchus).  In  accord- 
ance, too,  with  their  mode  of  life,  sense-organs  in  the  form  of 
eyes  and  probably  of  tactile  papill*  on  the  skin  occur,  and 
furthermore  the  processes  of  development  are  much  simpler 
than  in  the  endoparasites,  as  will  be  seen  later. 

Some  peculiar  anomalies  occur  in  the  life-histories  of  some  of  the  Poly- 
stomeae,  as,  for  instance,  in  the  Gyrodactyhis,  which  lives  upon  the  gill?  of 
the  Carp.  It  is  a  viviparous  form,  and  the  young  while  still  within  the 
body  of  the  parent  may  already  have  become  mature  and  contain  young 
likewise,  which  again  may  contain  ova  in  course  of  development,  four  gen- 
erations being  thus  enclosed  one  within  the  other.  Di^lozoon,  which  livts 
likewise  on  the  gills  of  Cyprinoid  fisiies,  is  peculiar  in  that  at  tiie  time  of 
sexual  maturity  two  individuals  become  fused  with  one  another  in  the 
form  of  an  X,  the  fertilized  ova  giving  rise  to  a  single  form  formerly 
known  as  Diporpa. 

2.  Order  DistomesB. 

This  order  includes  endoparasites  which  show  a  more 
marked  degeneration  than  do  the  members  of  the  preceding 
order.  Eyes  may  be  present  in  the  young  but  are  absenl 
in  the  adult,  and  furthermore  a  very  complicated  metamor- 
phosis is  passed  through  in  the  development.  The  suckers 
for  adhesion  to  the  host  are  either  one  {Monostomnm)  or 
two  {Distomum),  and  as  a  rule  no  chitinous  hooks  are  pres- 
ent. 

A...oiig  the  more  interesting  members  of  this  order  are  Distomum 
liepatimm,  a  large  form  measuring  2-3  cm.  iu  length  and  inhabiting  tho 


148 


iNVKitTRimATK  MouriroLoa r. 


biliMhioIrt  of  Shoop,  in  wlii(!l»  it  pnMluoos  vviiuL  is  toniiod  V.w  "  Uof,"  wliicli, 
in  tht>  low-iyiiiK  pasf.ims  of  KuKluntl  and  tiio  (lontinont,  is  I'nM.iiontly  tlu) 
cans."  of  llKHloslniclion  of  larjjjo  nnml»ors  of  slioop.  in  oxct*pl'ional  casos 
il  lias  boon  k-nown  to  owur  in  man.  In  K^ypl.  liowcvcr,  tlir  l<ollaii(.;.n 
aiv  nol  nnfrtMintMilIy  attacked  l)y  anoMuM-  form,  fhsfomitm  /i<n,iiif„l,iuni, 
wlticii  is  poi'uliai-  in  Dial,  contniry  to  tlio  ruli>,  tlm  so.xos  jiff  scpMnilod  ii'i 
<li(ri'ivnt  individuals.  TIio  nmrjjins  of  tlio  body  of  Hk^  male  an*  roiiiid 
inwiirds  on  tlio  vonlral  snrfaiv,  forming  a  tubo  wit  Inn  whicb  tlm  moroslcn- 
iWv  iVinalo  livos.  Assooialod  in  pairs  in  this  way,  tlioy  arc  fonnd  in  llir 
liloodof  tho  portal  vtMn  and  its  C(.nncclions  and  j)ass  I'o  the  nn>tcrs  and 
bla<ldcr.  in  whoso  nnicons  mcnd)ra:ic  Ihcy  deposit,  Micir  ova,  thns  pro- 
<lucinK  i>ii  iiillanunation.  accompanied  by  suppuration,  of  these  organs. 

Di'vclofwicvf  of  f/iv  Tmttn(<uf,>s.~-'n)o  ova  of  Tronuitodii 
consist  of  two  ilistinrt  j  jirts,  a  j>vnii-coIl,  tlu^  i>rotluct  of  tlio 
ovary,  surroumltMi  Uy  a  inaH.s  oi  food-niaiiMial,  the  socrotion 
of  tho  vitellaria,  tlio  wliolo  boiii^;  oucIosimI  in  a  sluUI  fonnod 
by  tlie  slioll-n;lniu].  In  tlio  roljstoinoni  tho  (lovtih)j)nioiit,  as 
a  ndo,  is  initiivlv  carriotl  on  ontsido  tho  body  of  tho  ])anint, 
tho  stalkod  ova  boing  attached  to  tlio  body  of  tho  host,  tii(>u<,'h 
(jifrH^driifhis  is  vivi|)arous,  in  tho  Distoiuoas  Iiowover,  th(* 
rovoiso  is  tho  iido,  tho  ova  iuuh>i{roiiio;  u  cortain  part  of  thi>ir 
dovolo|)iiioiit  ill  tlit^  utorns  *)f  tlu^  i)aront,  and  loavin^'  tli.^  o'u^ 
shortly  after  its  oxtrnsion  as  a  larva,  sonietinios  ciliated, 
soiiiotinios  provided  in  the  plaoo  of  tho  cilia  with  a  strncturo- 
leaii  cutu'lo,  and  furthornioro  in  those  ondoparasites  tl>er<> 
occurs  a  reniarkablo  alternation  of  ^'onorations  of  the  kind 
already  referred  to  as  liotoroji;ony  (see  p.  (51). 

The  lu'torogony  may  be  of  various  (h^<vroos  of  complexity. 
It  begins,  however,  in  nW  cases  with  the  (>nibryo  (Fi^^  7<),  J\ 
which  may  bo  a  free-swim mini>-  ciliated  organism  i)rovido(i 
with  a  short  pouch-shaped  intestine  and  with  a  mouth,  and 
froipioutl  possessin«;t  also  a  nervous  system  and  })i}rnuMit 
.\ve-spot  ad  well  as  excretory  tubes  ;  in  other  cases,  however, 
as  stated,  the  embryo  is  destitute  of  cilia,  usually  in  this  ca,j;e 
beino;  pro\ided  with  one  or  more  spines  at  the  mouth-end 
of  the  body,  and  all  gradati()ns  of  dej^eii oration  of  the  eve- 
spot  and  nervous  system,  as  well  as  of  the  excretory  tub(>s 
and  dicrestive  system,  may  bo  observed.  In  all,  however,  tho 
space  between  the  more  or  less  developed  di^^estivo  tract  and 
the  body-wall  is  occupied  by  uumerous  uuspecialized  cells 


TYPE  I'LA  TYlIKLMINTriKS. 


149 


(;/<;),  whicl  are  'n  reality  gorm-c,3llH  or  ovu  cai)a],le  of  under- 
«oinK'  a  i,artlien(,g,„iotic  dovolopmeiit.     EvxMitnally  tliis  larva 
u   it.   way  int.,  thn  interior  of  an  anin.al  of  „ome  kind 
usually  a  Mollu.sk,  and  there  undergoes  a  further  develon' 


...ent,  either  retaining  ,t,s  .ligostive  apparatus  and  elongating 
somewhat  to  loriu  a  JMia  (Fig.  79,  JJ),  or  beeondng  an  oval 


Fm.  79.-^,  CiliHtod  larv,v,  and  B,  Redla  of  Distomum  hepnticum  (after  l^cck- 

AIIT). 

d  =  intcslino.  ,„  ^.  „Hiiitli. 

ffc  =  gorm-,oils.  ,•■  =  second  gen.Tntion  of  R,,,li,c. 

sac  without  mouth  or  digestive  tract,  the  Sporocyst.  The 
Kedia  iH  a  niueh  more  liighly  organized  form  than  the  Sporo- 
cystand  is  fnupiently  capable  of  motion,  two  blunt  proiec 
t.oHs  near  the  hinder  end  of  the  body  serving  as  supports  in 
a  somewhat  similar  manner  to  the  sucker-like  feet  of  cater 
pilhirs  It  adheres  to  the  wall  of  a  cavity  of  its  host,  from 
winch  by  energetic  action  of  its  muscular  pharynx  it  is  able 
to  absorb  nutrition. 

From  this  stage  onwards  the  development  varies  in  com- 
plexity m  various  forms.  It  is  simplest  in  Momstommn  muta. 
/"/^S  whose  ciliated  embryo,  while  still  free-swimming,  contains 
within  1  a  small  sexually  immature  Monusfomum,  and  after  it 
1ms  made  its  way  into  the  interior  of  its  Molluscan  host  the 
:.<niugJ/ono5^mMm  becomes  eucapsuled  in  the  tis-ne- -f  it- 
nost.     The  mode  of  origin  of  this  immature  form  has  not  as 


150 


INVERTEBRATE  MORPHOLOGY. 


VB 


d_ 


yet  been  observed,  but  there  is  no  reason  for  doubting  that 
It  IS  the  result  of  the  parthenogenetic  development  of  one  of 
the  germ-cells  which  occur  in  the  bodj-cavity  of  the  embryo. 
So  long,  however,  as  it  remains  in  the  tissues  of  the  Mollusk 
It  undergoes  no  further  development;  it  can  only  reach  ma- 
turity in  a  second  host,  in  this  case  some  water-bird  which 
swallows  the  Mollusk  and  its  encapsuled  parasite,  when  the 
latter,  its  capsule  being  dissolved  by  the  digestive  juices  of 
the  bird,  IS  set  free,  fastens  itself  to  the  wall  of  some  of  the 
cavities  of  its  host  and  becomes  sexually  mature. 

In  this  species  of  Trematode  but  two  hosts  are  required 

in  the  life-history;    in    the  majority 
of  the  DistomesB  a   third   occurs,  an 
additional  stage  of  development  in- 
terveuiug  between  the  Kedia  or  Spo- 
rocyst  and  the  encapsuled  immature 
worm.     The  germ-cells  of  the  Redia 
or  Sporocyst  while  in  the  interior  of 
the   Mollusk    develop    into    a    form 
resembling    an    immature    Distorae, 
but  provided  with  a  mobile  muscular 
tail  whose  axis  is  formed  by  a  fibrous 
rod  resembling  somewhat  in  appear- 
ance the  Vertebrate  notochord.    Such 
an  organism  is  known  as  a  Cercaria 
(Fig.  80),  and  when  fully  developed 
the  Cercaria  brood  leaves  the  body 
of  the  parent    Redia    or   Sporocyst, 
makes  its   exit  from    the   tissues  of 
Fig.    90.— Cercaria    armata  the    Mollusk    and    leads    for   a   time 

(after  Schwarze).  „     f„  •  ■  •    ,  ^ 

«*=a..tenor  sucker.  ^  free-swimming  existence.     Eventu- 

cv  =  coutractile  vesicle.       ^^^7  ^^^^  Cercaria  makes  its  way  into 
rf  =  intestine.  the  body  of  a   second  host,   usually 

M  =  "bar'nx"'  '"^^'  "^^  *^^  ^""^^    ^   Mollusk,  and  there 

«P  =  sphi'e^"'''  becomes    encapsuled  in  the  tissues, 

m  =  ventral  sucker.  losing  at  the  same  time  its  tail,  and 

it  reaches  its  maturity  only  after  the 

Mollusk  has  been   swallowed   by  the  definitive  host,  as  was 

the  case  in  Monostomum. 


Simple  M( 

0/  _ 

1  Embryo. 

Hporocy.st 
or  Redia 

a 
0 

S   1 

V 

Encapsuled 
Distoine 

0     1 

TYPE  PLATYUELMINTHES.  151 

A  still  further  complexity  is  found  iu  the  L^ver  Fluke 
Disomum  hepaticum.    In  this  form  the  free-swimming  embryo 
makes  its  way  into  the  tissues  of  a  small  snail  and  there  be 
comes    converted   into  a  Sporocyst.     The  germ-cells  of  the 
Sporocyst  give  rise  by  their  development,  not  to  Cercari^ 
as  in  the  usual  cases,  but  to  Kedic^,  and  these  may  give  rise 
under  certain  conditions  to  a  second  brood  of  Kedi^  (Tm  79 
/>,  r).     During  the  summer,  however,  the  Kedic-e  produce  Cer' 
caria3  which,  leaving  their  host,  swim  about  for  a  short  time 

I  lusT^^ir^'"'  ^'^"^^^^^-'  ^^'  necessarily  in  a  second 
31ollusk,  but  on  grass  or  any  other  object  with  which  thev 
may  come  in  contact,  the  tail  at  the  same  time  being  lost 
If,  now,  these  encysted  forms  are  swallowed  by  a  sheep  the 


Simple  Mode. 

i  - 

I  Embryo.       Water. 

Sporocy.st 
or  Redia 

I.  Host 
(Mollusk) 

a 
0 

a 
0 

1     1 

V 

Eiicapsuled 
Distoine 

I.  Host 
n.  Host 

1 
a 

Mature 
Distonie 

V 
hH 

Usual  Mode. 


Kiiibryo.    !    Water. 


Spoi-ocyst  j   I.  Host 
or  Redia   l(Mollnsk) 


Cercari8B. 

Encapsuled 
Distome 


Water. 


Complicated  Mode. 


0)  _ 

£.2 


Mature 
Distome 


II.  Host. 


III.  Host 


Embryo.  Water. 


Sporocyst 


I.  Host 
(Mollusk) 


a 
a 
O 


Red  i  88 


CercariBB.         Water. 


Encapsuled 
Distome 


Matui'e 
Distome 


H.  Host  or 
on  {fiass,  etc. 

III.  Host 


fjenus  Holo^tomum,  who.se  e.nbrv  '  aft  n   ml         V  "  '"'^'"'^^  "^  *''« 

;;.e  «.t  host,  see.s  to  ^:t^izz:^:^z::':^' '^'y  ^^^ 

D'stome,  without  any  alternatio.)  of  generations  immature 

A  very  peculiar  life-liistorv  is  found  in  n,\fn„>„,» 

^^  parasitic  in  insect-eating  birds.     tLIo.^^^^^^^^  ^^'^'^'I' 

is  peculiar  in  that  it  asstunes  a  br      hinrfo'      he  h  \"  ''""''  ^"' 

network  among  the  tissues  of  the  ho  t       "uhlends  o   .^  ?  '''''''''''  '' 
work  young  Distomes  develop  without  th     n  er  enion  ofTc      "'■  ""'  '"^- 

'"Hl  by  their  development  and  its  own  l'i  nvf.  tlT  ?''""'''  '*^^'^' 


152 


INVEliTEBHATE  MOliPlIOLOG  Y. 


m 


hi 


it 

4 


tlie  snail,  wliich  tluis  become  enormously  distended.  Tlie  club-shaped 
structures  so  formed  are  abundantly  supplied  with  muscle-fibres,  and  bv 
visrorous  movements  linally  burst  the  distended  wall  of  the  tentacle,  and 
separating  from  the  Sporoeyst  fall  to  the  ground.  There  tiiey  ni()v,> 
about,  resembling  an  insect  larva  in  gen(>ral  ai)pear:ince,  a  resemblan-e 
iucreased  by  banded  markings  of  green  and  white,  which  render  them  very 
coM.spicuous,  and  they  are  apt  finally  to  be  snapped  up  l)y  some  bird,  iu 
whose  digestive  tract  tlie  young  Distomes  are  set  free  and  become  matui'e. 
There  can  be  little  question  but  tiiat  tiie  .simple  metamorpliosis  of  ihc 
Pbli/stome(z  represents  the  original  method  of  development  of  the  Trematoda, 
tlie  heterogony  characteristic  of  most  DistomecB  being  a  secondary  accpusi- 
lioM  developed  in  accordance  with  their  ondoparasitism.  An  ich  a  of  llic 
mode  in  which  this  alternation  of  generations  has  been  l)rought  about  is 
furnished  by  such  forms  as  Qyrodactylus,  in  which  the  development  of  tlio 
ovum  takes  place  witliin  the  body  of  the  parent,  the  young  in  (heir  turn 
developing  embryos  before  being  borti  (see  p.  147).  Tills  acceleration  of 
sexual  maturity,  accompanicjd  by  parthenogenesis,  has  l)r()ught  about  (lie 
condition  seen  in  the  Sporocyst  or  Redia,  which  are  embryos  provided  witii 
ova  capable  of  parthenogenetie  development.  Thus  fundam(>ntally  the 
heterogony  is  a  piedogene^pis  (see  )).  60),  and  may  b(;  compared,  in  a  gen- 
eral way,  with  the  formation  of  a  hydroid  colony  by  the  budding  of  a 
medusa  larva. 


III.  Class  Cestoda. 

Like  the  Treniatoila  the  members  of  this  class  are  para- 
sites, but  are  throughout  eii(h)i)arasit('s,  and  i)i'eseiit  a  much 
j,'reater  degeneration  of  structure  than  is  found  in  the  Disto- 
niPflB,  accon)panied  bj  peculiarities  of  development  dil}erin,^' 
somewhat  from  wliat  occurs  iu  these  forms.  The  Cestodes 
or  Tai)e worms  lack  all  trace  of  a  di<,'estive  tract  and  of  a 
mouth,  living  in  their  mature  state  attached  to  the  wall  of  tlie 
digestive  tract  of  their  host,  and  immersed  in  the  nutriti\e 
fluids  contained  in  the  intestii.'c. 

In  some  forms,  such  as  Cin-j/ophj/Utrns  (Fig.  81,  ^I),  para- 
>4itic  in  the  intestine  of  Cyprinoid  fishes,  the  similarity  <n  a 
'J'rennitode  is  very  striking,  except  in  the  ab.sence  of  sucKns 
for  adhesi(m  and  of  a  dig(>stive  tract.  The  worm  consists  ot  a 
somewhat  dilated  head,  succeeil'nl  by  auarrower  portion  which 
may  be  termed  a  nock  and  gradually  enlarges  to  the  ratlier 
cylindrical  body,  which  contains  a  single  set  of  reproduclive 
organs.  In  Li)/nl,i,  which  is  found  in  the  intestine  of  aip.iatic 
birds,  there  is  likewise  an  .ihsenco  of  suckers,  but  the  re]>ro. 


TYPE  PLATYHELMINTIIES.  153 

(luctive  organs  are  present  in  sever-.]  «pf« 

other,  without  any  extpr.nl  i  TV  succeeding  one  an- 

■  '^i^,<iJJb  IS  indicated,  Iiowpypt   t^vfo,.,,   n     1      •    ■,. 

liuct  constrictions  of  fl>«  1.    i     '''^'\<^^ei,  extevnallj  by  indis- 
ictions  ol  the  bodj,  an  indication  of  a  tendency 


.   L.  iiiilLiioi  eutl  of  7.  «(fr/<««<a  (after  I.euckabt) 
I'f  -  oviduct.  ,a  ^  „,,  ,,^.^^.,.^, 

«p  ovary.  «/ =  yoIk-Kl-ml^. 

«'«  =  vesiculu  seiniimlis. 
'<"•  the  individual  to  sepamto  into  a  number  of  nnrf«  .    1 
l'--HsmK  a  certain  unun.nt  of  individu    itv      tL^ 
-;l.es  its  iHghest  dPveh>pnH,nt    nui;J^,V /;'?'' 
i-rtion.  th«  .^.r^F^-'si    ;-f^'  "^"f \^'*''^'^.^«*  "^  -'  -"terior 
tlie  form  of  Huckers.  accompanied  or  not  by  chitinous 


154 


INVERTEBRATE  MORPHOLOGY. 


hooks  and  followed  by  a  varying  number  of  segments  or  pro- 
glottides, each  possessing  a  set  of  reproductive  organs  and  cap- 
able of  separating  from  its  fellows,  maintaining  for  a  time  an 
independent  life.  The  proglottides  towards  the  hinder  end 
of  the  chain  or  strohila  are  the  most  advanced  in  development, 
and  one  after  another  drop  off  and  pass  to  the  exterior  of  the 
host's  body  with  the  fieees ;  more  anteriorly  the  proglottides 
are  sexually  immature,  and  still  nearer  the  scolex  they  are  to 
be  found  in  various  stages  of  formation.  In  fact  the  hinder 
end  of  the  scolex  may  be  regarded  as  a  zone  of  growth,  new 
proglottides  being  successively  formed  at  this  region.  The 
process  of  proglottid  formation  resembles  not  a  little  what 
has  been  described  as  the  non-sexual  reproduction  of  the  Dis- 
comedusai,  the  scolex  corresponding  to  the  jiarent  Scyphos- 
toma  and  the  proglottides  to  the  Epliyra?,  the  entire  aggre- 
gation in  both  cases  being  termed  the  Strobila. 

The  exterior  of  the  body  of  a  Cestode  is  formed  by  a  cuti- 
cle without  any  trace  of  cellular  structure,  and  is  perhaps  to 
be  regarded  as  a  basement-membrane,  the  ectoderm,  originally 
present,  having  disappeared.  The  cuticle  varies  mucii  in 
thickness,  and  is  throughout  traversed  by  fine  pores  which 
allow  of  the  absorption  into  the  body  substance  of  the  nutri- 
tive fluids  in  which  the  Tai)eworm  lives,  either  directly  or 
by  permitting  the  passage  to  the  exterior  of  fine  protoplasmic 
processes  from  the  subjacent  tissue.  Special  developments 
of  the  cuticle  in  the  form  of  chitinous  hooks  are  frequently 
present,  arranged  in  some  Ta-nias,  for  example,  in  a  double 
circle  upon  a  prominence,  the  rostellum,  at  the  apex  of  the 
scolex,  and  forming  a  very  eflicient  means  of  attaching  the 
worm  to  the  wall  of  the  intestine  of  its  host.  Beneath  the 
cuticula  there  is  to  be  found  a  very  thin  muscular  layer,  tlic 
peripheral  musculature,  but  the  main  bulk  of  the  musculM- 
ture  consists  of  those  fibres  which  traverse  the  parencliynia. 
These,  especially  the  longitudinal  and  transverse  ones,  are 
massed  into  strong  bands,  the  former  lying  usually  exterior 
to  the  latter,  and  both  eucl<»sing  a  central  mass  which  is  trav- 
ersed by  weaker  bundles  of  dorso-ventral  muscles,  and  con- 
tains tiie  reproductive  a]i})arntus. 

In   connection   with    tiie  muscular  system   mny  be  mni- 


TYPE  PLATYHELMINTIIES.  166 

tioned  the  suckers  which  frequently  occur  upon  the  scolex 
and  serve  with  the  hooks,  when  these  are  present,  to  attach 
tlie  j.arasite  to  its  host.  In  Timia  these  suckers  are  four  in 
muaber,  and  have  the  form  of  circukr  depressions  whose 
walls  are  nchly  supplied  with  muscle-fibres,  while  iu  Bothrio 
cephalus  they  have  the  form  of  elongated  grooves,  situated  on 
the  edges  of  the  somewhat  flattened  scolex. 

As  might  be  expected  from  the  great  development  of  the 
muscles,  a  well-defined  nervous  system  is  present.     It  consists 
of  a  brain  lying  imbedded  in  the  tissues  of  the  anterior  por- 
tion  of  the  scolex,  evidently  composed  by  the  union  of  two 
ganglionic  masses  and  giving  rise  to  two  main  nerve-cords 
which   pass    backwards   through   the   entire   lenr^th   of    the 
strobila  without  interruption  (Fig.  82,  n).     So,  too,  the  excre- 
tory system  (Fig.  82,  ne)  extends  through  the  entire  strobila 
uninterruptedly.     It  consists  of  two  nephridial  tubes,  which 
m  the  anterior  part  of  the  scolex  may  be  united  by  a  cross 
branch,  as  they  are  at  the  posterior  edge  of  each  proglottid 
and  open  to  the  exterior  by  a  pore  situated  at  the  centre  of 
he  posterior  edge  of  the  last  proglottid.     After  the  loss  of 
he  original  terminal  proglottid  two  pores,  corresponding  to 
the  extremities  of  the  longitudinal  tubes,   place  the  system 
HI  communication  with  the  exterior. 

The  reproductive  system  (Fig.  82)  possesses  a  complexity 
similar  to  what  has  been  described  for  the  Tremaioda.  and 
lernrnphroditism  prevails  throughout  the  class.     In  the  stio 
lulnr  Cestodes   each    proglottid   contains  a  complete   set  of 
organs,  both  male  and  female ;   the  testes  (Fig.   82    te)  are 
n^sually  very  numerous,  consisting  of  small  spherical'  masses 
scattered  through  the  parenchynut.  each  being  provided  witii 
a  sn.all  duct,  which  after  a  short  course  unites  with  sinular 
<lucts    coming   from    other   testes,    all   finally   uniting   to    a 
snigle  vas  deferens  (nf),  which  ,>peus  to  the   exterior  after 
passing  through  a  muscular  organ,  the  cirrus-sac,  by  the  con- 
tractum  of  which  its  terminal  portion,  often  provided  on  its 
mnor  surface  with  barbed  hooks,  i,s  protruded  to  the  exterior 
as  an  mtromittent  organ  or  cirrus  (r,.     The  female  aunarnt.w 
vanes  somewhat  in  its  arrangeu.ent.    In  the  majority  of  fornis 
the  ovary  is  a  bilobed  organ  (o.).  lying  near  the' posterior 


156 


INVEliTEBKA TE  MOltPlIOLOG Y. 


end  of  the  proglottid.  The  oviduct  soon  after  leaviug 
the  ovary  unites  with  the  yolk-duct  {vid)  coming  from  the 
albuminous  vitellarium  {vi),  which  consists  of  a  number  of 
glands  scattered  through  the  parenchyma  similarly  to  the 
testes.     At  the  point  of  union  with  the  yolk-duct  the  oviduct 


Fm.  82.— PROOLOTTIO  o.'  T<pnia  JitieoUis  {atterKn^KMRH). 

c  =  cinus.  (e  =  testis. 

n  =  iR-ive.  tit  =  ulcnis. 

ne  =  e.xifLlory  cimal.  va  =  viigina. 

<"'  =  "V'"'.^'  rd  =  viis  (Ifferciis. 

iff  =  Hht'll-glaiid.  ri  =  yolk-gliind. 

(•/(/  =  yolk-durt. 

enlarn^es,  receiving  at  the  oulargen.eiit  the  secretion  of  a  nnm 
l)er  of  unicellular  glands  comiH)sing  the  shell-gljind  (sv 
From  thi^  enlargement  two  tubes  arise  :  one,  the  nx/hni  {r,>  , 
ruDH  almost  dii^ctly  f<n-ward  to  open  into  a  chanibor,  tin' 
genital  atnnm,  which  contains  also  the  cirrus-sac  and  com- 
inniiicttte«  directly  Tviih  th^  exterior;  while  tho  other,  the 
ttteruM  (ut),  after  a  somewhat  convoluted  ctnirse  opens  inde- 


P 


pendenti] 

The  vagi 

copulatio 

sides  of  i 

]h  146),  w 

iiud  matuj 

pore  is  in 

glottid ;  i: 

the  progh 

opening  ii 

tion  in  su 

Ticuias    tl 

Bothrioce} 

stead  of  ; 

opening  t( 

become  h 

punch-like 

JJcvcIoj 

in  the  arn 

in  the  dev 

('eph(du,s  (t 

group)   th( 

which  the 

egg  in  the 

six  chitino 

After  swill 

thrown  of}', 

hody  of  tl] 

cyst,  withii 

be  swallow 

the  walls 

st'xiially  m 

In   tho 

volk-cells 

relatively  s 

out  are  de 

of  liothr{(H'i 

H3,  A).     t» 

host,  in  wh 


TYPE  PLATYIIELMINTIIES. 


157 


pendeutiy  to  the  exterior  a  little  behiiul  the  genital  pore. 
The  vagina  serves  as  a  duct  for  the  spermatozoa  during 
copulation,  and  corresponds  with  the  canals  opening  at  the 
sides  of  the  anterior  end  of  the  body  in  the  Polystoniefo  (see 
)).  146),  while  the  uterus  serves  for  the  retention  of  fertilized 
imd  mature  ova.  In  Bothriocephalm  the  opening  of  the  genital 
])ore  is  in  the  middle  line  of  one  of  the  surfaces  of  tire  pro- 
glottid ;  in  Taniia,  however,  it  occurs  on  the  lateral  margin  of 
the  proglottid,  and  in  some  cases  each  proglottid  may  have  an 
opening  in  each  of  the  lateral  margins,  there  being  a  dujdica- 
tion  in  such  cases  of  the  genital  ducts.  Furthermore,  in  the 
Tamias  the  vitellarium  is  much  less  voluminous  tlian  in 
Bothriocephalus,  and  produces  an  albumen-like  secretion  in- 
stead of  yolk-cells,  and  in  addition  the  uterus  has  no  special 
opening  to  the  exterior  and  is  relatively  small,  though  it  may 
become  fairly  voluminous  by  its  walls  being  pushed  out  into 
pouch-like  sacculations  by  the  contained  ova. 

Development  of  the  6'.?.s'^(;(t.— Accompanving  tlio  differences 
in  the  arrangement  of  the  rejjroductive  apparatus  differences 
in  the  development  are  found  iu  the  two  groups.     In  Botlirio- 
cephdm  (taking  this  form  again  as  the  example  of   the  one 
group)   the  egg   is   richly  })rovided    with  yolk-cells,    among 
which  the  germ-cell  lies  imbedded.     The  embryo  leaves  the 
egg  in  the  form  of  a  spherical  ciliated  body,  provided  with 
six  chitinous  hooks,  arranged  more  or  less  distinctly  in  jairs. 
After  swimming  about  for  a  time  the  cilia  and  tlieiV  cells  are 
thrown  off,  and  the  six-hooked  embryo  makes  its  way  into  the 
l)ody  of  the  first  host,  where  it  becomes  enclosed  in  a  tliJn 
cyst,  within  which  it  develops  directly  to  a  scolex.     If  this 
be  swallowed  by  the  second  host,  the  "worm  fastens  itself  to 
the  walls  of  the  digestive   tract,  and    soon  develops  to  the 
sexually  mature  strobila. 

In  the  Taniias,  however,  the  ova  are  much  smaller,  the 
yolk-cells  being  replaced  by  an  albumen-like  -ibstanee, 
ivlatively  small  in  amount,  and  the  embryos  when  they  hatch 
out  are  destitute  of  cilia,  resembling  the  six-hooked  embryo 
of  liot1m<m'ph,ln.s  after  it  has  lost  its  ciliated  covering  (FJg. 
Hy,  A),  In  this  condition  it  makes  its  way  into  the  iirimaiy 
host,  iu  whose  tissues  it  b(?comes  encysted,  and  develops  iu 


158 


INVERTEBRATE  MORPIIOLOOY. 


some  forms,  such  as  the  Tcenia  cucumerina  of  the  dog,  whose 
primary  host  is  the  Dog-louse,  into  a  Ctjsticercoid.  Tliis  reseiii- 
bles  a  scolex,  whose  head  has  been  withdrawn  into  and  enclosed 
by  the  body,and  when  it  is  swallowed  by  the  secondary  host,  the 
dog  in  the  instance  cited,  the  head  is  pushed  out,  fastens  itself 
to  the  wall  of  the  digestive  tract,  and  begins  to  grow  and  form 
proglottides.  In  other  cases,  however,  the  posterior  part  of  the 
scolex  into  which  the  head  is  retracted  becomes  enormously 
swollen  by  the  accumulation  of  fluid  within  it,  forming  a  large 
vesicle,  into  the  interior  of  which  the  head  projects,  having 
become   completely  invaginated.      8uch   a  form   as   this  is 


Pio.   83.-4,  six-booked  embryo  of  Tmnin ;  /?,  din,cram  of  Cysticercus ;  C, 
dmgnuu  of  Vanurus;  D,  (liiii,nuiu  of  Echinococcus. 

termed  a  Cysticercus  (Fig.  83,  />'i ;  when  it  is  swallowed  by  the 
-secondary  host  the  head  evaginates,  and  the  cyst  remains  for 
some  time  attached  to  the  hinder  end  of  the  scolex,  but  later 
disappears,  and  the  formation  of  the  proglottides  occurs. 
Further  modifications  arise  by  the  formation  in  the  wall  of  tlic 
cyst  of  not  only  one  but  several  invaginated  heads,  forming 
the  Ccenurv.s  (Fig.  83,  O) ;  or  even  secondary  c.ysts  may  ariso 
from  the  inner  wall  of  the  original  vesicle,  and  each  of  them 
m».j  develop  several  heads,  forming  what  is  known  a,s  the 
Echinococcus  (Fig.  83,  D). 

Rovoral  of  tho  Cestoda  are  especially  interesting  from  a  madJral  stan.l- 
poiiit,  inusmuch  as  tliey  are  parasitic  in  man  eitiier  during  the  adult  or  tlic 


TYPE  PLAT YHELMIN TEES. 


159 


larval  stage.  Among  these  may  be  mentioned  Bnthriocephalus  latus,  which 
occurs  in  the  iiuman  intestine,  where  it  may  reach  a  length  of  as  much  as 
13  metres,  in  such  cases  consisting  of  many  thousand  proglottids.  These 
may  readily  be  recognized  by  tlie  convoluted  uterus,  and  by  the  open- 
ings of  the  reproductive  organs  on  the  median  line  of  one  oi  the  flat  sur- 
faces, while  the  head  is  characterized  by  being  flattened,  and  provided 
on  the  margin  with  two  elongated  suckers.  The  ova  give  rise  to  a  ciliated 
larva  which  becomes  transformed  into  the  six-hooked  embryo,  this  latter 
making  its  way  into  the  tissues  of  certain  fish,  which  serve  as  tlie  first  host. 
Man  becomes  infected  with  the  worm  by  eating  improperly  cooked  or  salted 
fish,  the  Pike  being  the  more  usual  primary  host,  though  this  part  may  also 
be  played  by  other  forms. 

Tlie  genus  Ttenia  furnishes  two  Iiuman  parasites.  The  genus  is  char- 
acterized by  the  head  being  providf<i  with  four  circular  suckers,  as  well  as 
in  some  cases  with  one  or  more  crowns  of  hooks  ;  the  genital  pore  is  situ- 
ated upon  the  margin  of  the  proglottids,  and  the  uterus  is  a  straight  tube 
with  a  varying  number  of  lateral  transverse  pouches. 

Tcenia  sagmata,  also  known  as  T.  mediocanellata,  is  by  far  the  most 
frequent  tapeworm  of  man,  and  may  reach  a  lengvh  of  7-8  metres,  and 
consist  of  1300-1300  proglottides.  The  head  has  no  rostellum  or  crown  of 
hooks,  and  the  proglottids  are  recognizable  by  their  size,  measuring  5-7 
linn,  in  breadth  and  18-30  mm.  in  length,  and  also  by  the  lateral  branches 
of  the  ucerus  being  slender  and  20  or  30  in  number.  The  Cysticercus 
occurs  in  the  muscles  or  occasionally  in  other  organs  of  cattle,  improperly 
cooked  beef  being  the  source  of  infection  for  man. 

Tania  solium  is  of  less  frequent  occurrence  than  T.  saginatn,  from 
which  it  is  easily  distinguished  by  its  shorter  length,  ?--^  metres,  and  by 
the  smaller  number  of  proglottids,  800-900.  The  head,  in  addition  to  the 
four  suckers,  is  provided  with  a  rostellum  bearing  a  double  crown  of  from 
36-28  hooks.  The  proglottids  are  about  5 -mm.  broad  and  10-12  mm.  long, 
and  the  uterus  has  7-9  stout  lateral  pouches.  The  Cysticercus  state  of  Lils 
worm  occurs  in  the  muscles  of  pigs,  -..hence  man  becomes  infected  by  eat- 
ing  improperly  cooked  or  salted  pork.  It  measures  8-10  mm.,  and  possesses 
when  imbedded  in  the  muscles  an  elliptical  shape,  its  long  axis  being  paral- 
lel with  the  long  axis  of  the  muscle-fibres.  In  addition  to  its  occurrence  in 
swin.!  muscle,  however,  it  has  also  been  found  occasionally  in  man,  en- 
(•ysted  in  the  muscles,  brain,  or  eye.  The  source  of  infection  of  ni;iii  is,  in 
many  cases  at  least,  cre.ss,  hsttiice,  and  such  articles  of  food  which  have 
been  watered  with  li<iuid  manure  containing  the  fertilized  ova  of  the  worm. 
The  six-hooked  embryo  which  developes  from  the  ovum,  migrates  to  the 
tissues  n.iuted  ivhero  it  encysts  itself,  and  man  becomes  the  intermediate 
host  of  the  worm. 

Ill  addition  to  being  occasionally  the  intermediate  host  of  T.  solium, 
man  may  also  be  the  host  of  the  Echinococcus  of  T.  echinococms.  a  small 
\\<mn  about  4  mm.  in  length  and  with  only  three  proglottids.  which  occurs 
in  its  adult  stale  in  the  intestine  of  the  dog.    Tho  ova  may  be  received  into 


i 


160 


m VERTEBRA TE  MORPIIOLOG  T. 


the  human  digestive  tract  by  fondling,  and  especially  by  kissing,  infected  pot 
dogs,  and  the  six-hooked  embryo  makes  its  way  to  the  liver,  lungs,  brain, 
or  otlier  organs,  where  it  becomes  encysted,  produ'jing  tumors  which, 
especially  in  the  liver,  may  reach  a  great  size  and  a  weight  of  from  10  to, 
i!i  .iome  cases,  15  kilogrammes. 

Domestic  animals  are  uLso  apt  to  be  infected  with  Cestodes  in  addition 
to  tiiofie  already  mentioned,  occasionally  with  fatal  results.  This  is  es- 
pecially the  case  with  sheep,  in  whose  intestine  T.  expansa  may  develop  in 
such  numbers  as  to  occlude  the  lumen,  and  cause  deatli,  especially  in  young 
iambs.  A  Ccenurus  also  occurs  occasionally  encysted  in  the  brain  of  siieep, 
producing  a  disease  known  from  its  symptoms  as  the  "staggers,"  wliicli 
may  likewise  result  fatally. 

The  Kelatiomhips  of  the  Cestodes. — In  considering  the  affniities  of  the 
Cestoda,  the  nature  of  the  strobila,  so  far  as  its  individuality  is  concerned, 
must  be  iiiquiri'd  into.     Two  views  upon  this  point  are  open.     The  older 
one  regards  the  Cestode  as  a  colony,  considering  each  proglottid  an  indi- 
vidual equivalent  to  the  scolex,  and  the  process  of  strobilation   one  of 
reproduction  by  budding.     Oil  tliis  view  the  strobila  is  exactly  comparable 
to  the  Scyphostoma  strobila,  the  scolex  corresponding  to  the  Scypliostonia 
base  and  the  proglottids  to  the  Ephyrte.     There  is  undoubtedly  much  to  be 
said  in  favor  of  such  a  view  which  regards  the  reproduction  of  the  Cestoda 
as  a  process  of  alternation  of  generations,  but  at  the  same  time  it  must  he 
recognized  that  the  buds  or  [)roglottids  are  not  ri'(lui)lications  of  the  \r.\\v\\\ 
bud  as  is  the  case  witii  Microstoma,  where  the  budding  individual  has  the 
adult  form.     In   the  Scyphostoma  strobila  the  buds  do  differ  from  the 
parent  which  gives  rise  to  them;  but  the  Scyi)h()slorna  is  a  larva  which 
gives  rise  by  budding  to  the  adidt  form,  and  is  comparable  rather  to  llic 
Cyst icercus  than  to  the  scolex  of  the  Cesloch;.     Non-strobilaling  Scyplios- 
tomas  become  medusa',  but  the  .scolex  nev(!r  becomes  a  proglottid,  and 
the  latter  cannot  be  considered  the  terminal  stage  of  the  life-history  in  ti;e 
same  sense  as  a  medusa  is.     The  nervous  system  of  the  entire  Cestode 
strobila  centres  in  the  brain  of  the  sc(jlex,  the  various  proglottids  ncvei 
developing  iiulependent  brains,  the  reproductive  organs  being  practically 
the  oidy  organs  which  are  reduplicated  in  successive  buds. 

According  to  the  second  view  the  strobila  h  \\  individual,  and  llie 
strobilation  is  regarded  as  a  culmination  of  the  redupIi(!ation  of  org.ins 
seen  in  many  forms,  but  more  especially  in  the  Nemerteans  (([.v.i.  This 
view  receives  strong  support  from  the  occurrence  of  such  forms  as  I'drii- 
ophjiHiiKs,  LiijithK  and  TrhniojiJionis,  desei'ihcd  on  u  preceding  page,  iii 
which  may  l)e  seen  successive  gradations  of  strobilation,  beginning  with  ,i 
simple  n!dui)lication  of  the  reproductive  apparatus  in  Lff/nla,  this  rediipli 
cation  being  accompanied  in  Tn'oiiophoriis  l)y  a  tendency  for  the  body  to 
constrict  into  parts,  each  of  which  contains  one  of  the  sets  of  reproductive 
organs. 

The  choice  between  these  two  views  hinges  upon  the  question  of  indi 
vidualify.     Tlie  individmility  of  either  Liijiihi  or  T/iauophorus  can  hardiv 


be  qucstioi 

as  an  indiv 

which  the 

colony  of  i 

aggregate  ( 

as   the  eel 

ratiier  the 

bud,  produ 

in  oiie  or  n 

the  testes, 

originally  f 

testes,  and 

the  entire  i 

being  prod 

series  to  be 

the  greater 

tain  amoun 

at  the  same 

process  of  i 

viduals  are 

Canjophylli 

certain  exte 

scolex,  but 

reality  an  ii 

Considei 

affinities  of 

todes,  the  si 

I«'ing  cai)ab 

tract  or  as  C 

indications  i 

with  the  bi( 

I'espect — Ar 

without  redi 

era  I  way  to 

indicate  tha 

Cysticercus 

ihtir  similari 

Uecently  su( 

coids  :   u  tai 

lii'cn  describ 

more  it  has  1 

I  lie  head  is  ii 

oil  becoming 

at  present  a 

Troraa  todes, 

been  establis 


TYPE  PLATYIIELMINTUES. 


IQl 


1)C  questioned,  and  there  is  no  reason  for  regarding  a  Tcrnia  for  instance 
as  an  individual  Ijclonging  to  a  higher  grade  than  either  of  these— a  view 
which  tlie  first  and  older  tlieory  implies,  since  it  regards  a  Tania  as  a 
colony  of  e(i.uvaleut  individuals.     «uch   a  form  as  Caryophylkeus  is  au 
aggregate  of  individualities  of  a  lower  grade,  organ-individuals  ;  and  just 
as  the  cell-individuals  composing  these  may  divide,  so  the  organs,  or 
ratiier  the  embryonic  masses  of  cells  destined  to  give  rise  to  them,  may 
bud,  producing  a  reduplication  of  organs.     This  reduplication  may  occur 
in  one  or  more  organs  ;  in  the  Acoila  among  the  Turbellaria  it  affec'ts  only 
the  testes,  in  the  Alloioccela  it  affects  both  ovaries  (tlie  vitellaria  being 
uriginally  parts  of  the  embryonic  mass  which  gives  rise  to  the  ovaries)  and 
testes,  and  in  the  Khabdoca^la  it  affects  only  the  ovaries.     In  the  Cestodes 
the  entire  reproductive  apparatus  is  reduplicated  in  this  mannei,  a  scries 
being  produced,  and   secondarily  a    tendency   for  each   member  of  the 
series  to  be  capable  of  separation  from  its  fellows  has  come  about  owing  to 
the  greater  certainty  it  gives  for  the  perpetuation  of  the  species.     A  cer- 
tain amount  of  individuality  of  the  progloftid.s  is  thus  brought  about,  but 
at  the  same  time  the  process  of  strobilation  cannot  accurately  be  ternied  a 
process  of  non-sexual  reproduction  l)y  budding,  since  the  proglottid  indi- 
viduals are  not  quite  of  the  same  g--ade  of  morphological  individuality  as 
Canjophyllmis,  which  the  scolex  represents.     Both  views  are  correct  to  a 
certain  extent :  the  strobilation  is  a  budding  off  of  individuals  from  the 
scolex,  but  of  individuals  of  a  lower  grade  ;  and  the  entire  strobila  is  in 
reality  an  individual  comparable  to  CaryophylUrns  or  a  Trematode. 

Considering,  then,  the  strobila  as  a  metamere-individual,  what  are  the 
amnities  of  the  Cestodos?    They  seem  to  have  been  derived  from  Trema- 
todes,  the  simpler  forms  without  reduplication  of  the  reproductive  or^-ans 
Ix'ing  capable  of  being  regarded  either  as  Trematodes  without  a  digeSive 
tract  or  as  Cestodes  without  any  indications  of  strol)ilati()n.     If  this  be  true 
indications  of  their  allinity  shoidd  appear  in  the  life-history  in  accordance 
with  the  biogenetic  law.     One  interesting  form  deserves  mention  in  this 
ivspect— Ayc/«r/(<fes,  which  occurs  in  certain  Annelids.     It  is  a  Cestode 
without  reduplication  of  organs  and  provided  with  a  tail,  similar  in  a  gen- 
enil  way  to  that  of  a  Cercaria.     Certain  facts  in  its  life-history  seem  to 
indicate  that  Archujetes  is  comparable,  not  to  an  adult  Cestode,  but  to  ;i 
Cysticercus  which  has  become  sexually  mature,  and  it  might  be'  expc-cteil 
iliiir  similarities  to  the  Trematode  Cercaria  might  bo  found  in  Cysticerci 
Ueeently  such  similarities  have  been  shown  to  exist  in  certain  Cyslicer- 
eoids  :   a  tail-like  ai)pendage,  which  later  separates  and  degenerates  has 
l"rn  described  as  occurring  at  this  stage  of  the  development ;  and  furthe'r- 
iiiore  it  has  been  suggested  that  the  cavity  of  the  Cysticercoid  into  which 
the  head  is  invaginated  may  be  equivalent  to  the  Trematode  intestine  later 
on  becoming  obliterated  by  the  growth  of  the  parenchyma.     The  •■vidence 
at  present  available  points,  then,  to  a  d(>rivation  of  the  Cestode  from  the 
Trematodes,  and  from  Trematodes  in  whicii  the  Cercaria-stage  liad  already 
been  established. 


162 


IN  VERTEBRA  TE  MORPHOLOO  7. 


IV.  Class  Xemertina. 
The  three  precediug  classes  show  marked  evidences  of 
genetic  affinity,  the  char;ieteri:stic  differences  of  structure  in 
the  Trematodes  and  Ce«todf^s  being  due  to  the  parasitic 
habits  of  these  forms.  The  Nemerteans,  on  the  othv  .  hand 
though  apparently  tracing  descent  from  a  Turbellarian-like 
ancestor,  show  a  marked  advance  in  structure,  and  must  be 
regarded  as  organisms  of  a  considerably  b7^]ier  grade  than 
the  other  Platyhelmiuths. 

They  are  for  the  most  part  marine,  though  a  few  forms 
^  inhabit  fresh  water  or  even  damp  earth, 

and    are    usually    elongated   ribbon-like 
forms,  reaching  a  length,  in   some  cases, 
of  several  centimetres.    The  body  is  ex- 
ternally  unsegmented,  though  a  more  or 
less  marked  metamerism  of  the  internal 
organs,  due  to  their  repetition  at  definite 
intervals,  may  be  present.     The  ectoderm 
of  the   body  resembles  that  of  the  Tur- 
bellaria  in  being  throughout  ciliated,  and 
rests  upon  a  basement  membrane,  which 
in   some   cases   contains   cells.      Within 
the  membrane  are  a  varying  number  of 
muscle    layers,    differentiations     of    the 
outermost   portions  of   the    mesodermal 
tissue,  which  in  the  form  of  a  parenchyma 
occupies  the  interval  between  them  and 
Fig.  84.-STirHosTEMMA  the  digestive   tract.     This  (Fi-    84  rf,  is 

Ell-HAUDI  (after  Montgo-  i  -       ,       •    ,  ,  ^     ^"  *      ''    '^ 

MERv).  ^"  almost  straight  tube,   except  in   the 

h  =  blood-vessels.  genus  J/alacoMelh,  and  is  pushed  out  ou 
c.  =  cerebral  ganglion,  each  side  into  sac-like  pouches,  which 
cfi' =  ciliated  funnel.        „,.a     ov,.o.>  ,.  i     •  . 

^  =  intestine.  ^'^     anauged    m    some    cases    with     a 

oc  =  eyes.  regularity    of    succession    almost   meta- 

ov  =  ovary.  meric.      It  opens  to  the  exterior  at  the 

F- =  proboscis.  anterior  end  of  the  body  bv  the  mouth 

rm  =  retractor  muscle.  ^  short  non-muscular  oesophagus  inter! 
veiling  between  the  intestine  proper  and  that  oi)ening  ■  and 
at  the  other  end  of  the  b.nly  is  a  second  communication' with 


TYPE  P'LATYIIELMINTIIES. 


163 


the  exterior,  the  anus,  an  opening  unrepresented  in  other 
Platyhelmiuths.  The  digestive  tract  is  no  longer  a  blind 
sac,  but  has  the  form  of  a  tube,  as  in  all  the  higher  types. 

lu  the  anterior  end  of  the  body,  above  the  digestive  tract, 
is  a  structure,  the  proboscis  (Fig.  84,  pr),  essentially  peculiar 
to  the  Nemerteans,  although  indications  of  such  an  organ  are 
to  be  found  in  the  Rhahdocxla.  It  consists  of  a  closed  tube, 
the  proboscis  sheath,  with  muscular  walls,  imbedded  in  the 
body  parenchyma  and  extending  backwards  in  some  cases 
almost  to  the  end  of  the  body,  and  within  it  lies  the  proboscis, 
also  a  tube,  united  to  the  wall  of  the  sheath  near  its  anterior 
end  aud  in  fact  closiug  it  at  that  region.  From  this  lino  of 
attachment  the  proboscis  stretches  back  in  the  cavity  of  the 
sheath,  the  space  between  it  and  the  walls  of  the  sheath  being 
filled  with  fluid.  It  is  a  simple  invagination  into  the  cavity 
of  the  sheath  of  the  external  body-wall,  whose  musculature 
as  well  as  ectoderm  are  coutiuuous  with  that  of  the  proboscis. 
From  the  tip  of  the  invagination  a  band  of  muscle  fibres, 
forming  the  retractor  muscle  {rm)  of  the  proboscis,  passes  to 
the  wall  ot  the  body.  By  the  contraction  of  the  muscular 
Avails  of  the  sheath  the  fluid  contained  in  its  cavitv  forces  the 
proboscis  to  be  evaginated  sometimes  with  sufficient  force 
to  tear  itself  loose  from  its  line  of  attachment ;  but  should 
this  accident  not  happen,  the  proboscis  can  be  reinvaginated 
by  the  contraction  of  its  retractor  muscle.  The  function  of 
this  organ  is  doubtful.  In  some  cases  it  is  undoubtedly  a 
weapon  of  oifence  and  defence  ;  but  it  seems  not  improbable, 
from  its  rich  nerve-supply  and  from  the  probable  function  of 
its  prototype  in  the  Rhabdocoela,  that  in  some  cases  at  least 
it  may  be  a  tactile  organ. 

A  well-developed  ervous  system  is  always  present,  though 
it  may  show  in  some  cases,  as  Carinellc,  the  primitive  character 
of  being  still  imbedded  in  the  ectoderm  or  else  lying  immedi 
ately  beneath  it.  In  other  cases,  however,  as  Cerebratulns,  it 
is  enclosed  in  the  muscles  of  the  body-wall  or  may  even  be 
completely  within  them,  imbedded  in  the  parenchyma.  It 
consists  in  its  most  usual  form  of  two  ganglionic  masses 
(Fig.  84,  ce)  from  which  short  nerves  pass  forwards  and  which 
iire  united  by  two  iransverse  commissures,  one  of  which  passes 


164 


INVERTEBRATE  MORPHOLOGY 


over  or  m  front  of  the  (Bsophagus,  wJule  tlis  otlier  arches 
from  oue  gau-houic  nuiss  to  the  otlier  over  the  proboscis 
sheath.      Each   gaugliou   is   bilobed,   the   smaller   posterior 
lobe  being  iu  some  cases  united  to  the  larger  one  bj  a  rela- 
tively thin   baud  of   uerve-tissue   so  that   it  appears   to  be 
almost  mdepeudeut.     From  the  larger  lobe  of   each   side  a 
nerve-cord  passes    towards  the  posterior    end  of    the  body 
whera  the  two  may  unite  to  form  an  arch  passing  over  the' 
posterior  part  of  the  intestine.     Iu  addition  to  these  a  third 
nerve  originating  from  the  comniissure  passing  over  the  pro- 
boscis sheath  and  running  backwards  in  the  median  dorsal 
line  IS  frequently  present  as  well  as,  in  some  forms,  another 
nerve  running  along  the  dorsal  wall  of  the  proboscis  sheath, 
to  which  it  sends  branches.     In  many  forms,  such  as  Cerehrai 
ulus,  a  fine  plexus  of  nerve-tissuo,  lying  between  the  muscle 
layers  of  the  body-wall,  unites  the  three  main  nerve-cords 
some  of  the  strands  of   the  plexus  being   sometimes  larger 
than  the  others  and  forming  circular  commissures  between  the 
nerve-cords ;  iu   Tetmstemma  and  AmpJuporus,  for   example, 
these  circular  commissures  may  be  strongly  developed  and 
have  an  almost  metameric  arrangement,  the  general  plexus 
being  in  such  cases  wanting, 

^  Eyes  (Fig.  84,  oc)  are  present  iu  some  forms  occasionally 
in  considerable  numbers,  but  are  frequently  wanting,  and  uto- 
cysts  occur  but  seldom.  The  lateral  ciliated  grooves  which 
occur  on  the  sides  of  the  head  of  some  Rhabdocoela  reach  in 
the  Nemerteaus  a  high  development  (eg),  in  some  forms,  e.g. 
Cerehratulus  and  Tetrastemma,  becoming  ciliated  funnels  of  some 
length,  whose  inner  ends  are  imbedded  iu  the  substance  of  the 
posterior  lobe  of  the  brain.  An  olfactory  function  has  been 
assigned  to  these  organs,  though  some  authors  have  consid- 
ered them  mainly  respiratory. 

The  excretory  system  consists  of  a  longitudinal  canal  on 
each  Side  in  the  anterior  portion  of  the  body,  sometimes  re- 
placed by  a  network  of  canals,  which  opens  to  the  exterior  by 
one  or  more  ducts  leading  to  pores  situated  on  the  margin  of 
the  body.  In  some  cases  these  lateral  ducts  and  the  pores 
may  be  quite  numerous  and,  like  the  intestinal  pouches  and  the 
circular  nerve-commissures,  may  have  a  somewhat  metameric 


moveman 


TYPE  PLA  TYIIELMIXTIIES. 


165 


arraugement.  The  various  termiual  branches  of  the  nei^hridial 
tubes  are  chib-shaped  aud  closed,  a  flame  of  cilia  projectiuj? 
from  the  closed  end  into  the  lumen  of  the  tube.  The  cajials 
aud  tubes  are  liued  with  ciliated  cells,  aud  are  therefore  inter- 
cellular and  not  intracellular,  i.e.,  do  not  perforate  cells,  differ- 
iuj,'  in  this  respect  from  the  nephridia  of  other  Platyhel- 
iiiinths. 

The  blood-vascular  system  is  peculiar  to  the  Nemertea 
among  Platyhelminths,  and  consists  in  the  simijle  forms,  such 
as  Carinella,  of  two  lateral  vessels  which  anteriorly  open  into 
lacunar  spaces  without  definite  walls.  In  the  more  highly 
organized  forms,  however,  three  longitudinal  trunks,  two 
lateral  and  one  dorso-mediau,  are  present  Avith  definite  and 
st)metimes  muscular  walls,  aud  unite  in  a  J_-shaped  manner 
at  the  posterior  end  of  the  body,  while  in  front  they  may 
(Uthor  oi)Pn  into  a  system  of  lacuna),  or  they  may,  as  in  Sficho- 
stemma,  unite  with  each  other,  a  perfectly  closed  system  thus 
resulting  (Fig.  85,  h).  Transverse  connecting  branches  be- 
tween the  dorsal  and  lateral  vessels  occur  in  regular  succes- 
sion, a  metamerism  being  again  suggested.  The  blood-vessels 
and  lacume  contain  a  fluid  in  which  float  round  or  elliptical 
corpuscles,  which  in  some  of  the  higher  forms  have  a  red 
color,  due  to  the  presence  of  haemoglobin.  No  heart  or 
special  contractile  organ  is  present,  the  blood  being  driven 
through  the  vessels,  without  any  definite  direction,  by  the 
movements  of  the  body. 


The  occurrence  of  a  blood  vascuiar  system  in  the  Nemerteans  and  its 
eliaracter  in  the  lowest  members  of  the  group  suggests  a  mode  of  origin  for 
the  system  which  agrees  well  with  what  may))e  deduced  from  embryological 
observations  on  other  forms.  It  may  be  supposed  tiiat  in  the  pi-imhive 
Nemerteans  a  system  of  spaces  filled  with  fluid  existed,  in  which  cells  derived 
Irom  the  parenchyma  floated.  Tliese  spaces  would  represent  a  simple 
ctelom,  and  were  lacunar  in  character,  lacking  definite  walls,  the  cir- 
culation of  the  fluid  they  contained  being  very  irregular.  In  time  tlie 
.spaces  along  the  sides  of  the  body  might  arrange  themselves  iu  a  linear 
manner,  and  might  acquire  definite  walls,  the  rest  of  the  spaces  remaining 
lacuiuir,  when  a  condition  resembling  that  in  Carinella  would  ensue,  tlie 
arrangement  found  in  higher  forms  resulting  from  the  couversiou  of  the 
remaining  lacunar  spaces  into  vessels  with  definite  walls. 

According  to  this  view  the  blood-vascular  system  is  to  be  regarded  as 


166 


INVEliTEBHA TE  MOHPIIOLOU  r. 


in  reality  ji  portion  of  tlie  coeloni  separated  off  for  a  special  purpose,  and 
otiier  instances  bearing  the  same  significance  will  Ijo  noticed  later. 

The  reproiluctive  Kjsteni  dirters  from  tluit  of  the  other 
Phityhelminths  iu  its  much  ^'renter  simplicity,  no  vitelhuia  or 
shell-ji;hiud  being  present,  unci  furthermore  tlie  Nemerteiiiis 
are  almost  without  exception  of  separate  sexes.  The  ovaries 
(Fig.  8-1,  ov)  or  testes  are  present  in  considei-able  numlxM's, 
cue  lying  in  each  interval  between  two  lateral  diverticula  of  the 
intestine,  so  that  they  partake  in  their  arrangement  of  the 
more  or  less  pronounced  metamerism  of  that  organ.  Between 
the  intestine  and  the  genital  masses  there  is  in  some  forms  a 
distinct  cavity,  or  ccelomic  si)ace,  and  at  tlie  time  of  maturity 
a  separate  communication  with  the  exterior  forms  for  each 
ovary  or  testis. 

The  class  Nemertiua  niay  be  divided  into  four  orders, 
whose  chief  characteristics  may  b(^  briefly  stated,  having  been 
for  the  most  part  already  described. 

1.  Order  Paleeonemertini. 

To  this  order  belong  the  genus  (JarineUa  and  allied  forms, 
all  characterized  by  structural  peculiarities  which  are  to  be 
regarded  as  i.rimitive.  The  lateral  ciliated  organs  are,  as  in 
the  Khabdocd'la,  mere  grooves,  not  being  continued  inwards 
to  the  brain  ii'  the  form  of  a  funn(d  ;  and  furthermore  the 
nervous  system  is  either  imbedded  in  tin?  ectoderm  or  lies 
immediately  below  it.  To  these  chnractiMs  may  be  added  the 
more  or  less  lacunar  nature  of  the  blood  vascular  system,  and 
the  communication,  in  some  cases,  of  the  nephridia  with  it. 

2.   Order  Schizonemertini. 

In  the  Schizonemertini  the  ciliated  funnels  are  well  devel- 
oj)ed,  and  the  nervous  system  is  imbedded  iu  the  muscular 
layers  of  the  body-wall  ;  and  though  the  nerve-cords  are  still, 
as  in  the  ])receding  order,  united  by  a  plexus,  nevertheless 
there  are  indications  of  a  dcn-elopment  of  commissural  con- 
necting nerves.  The  blood  vascuhir  system  is  still  lacumir 
anteriorly,  though  ])osteriorly  three  well-deHned  ve.SHels  are 
present.     The  genus  CVHn-dtnlnH  Ixdongs  here. 


This  ^ 

Amphipoi 

ciliated  fi 

complete] 

the  nerv< 

])lexus  be 

series  of  t 

most   stri 

structure 

(that  is,  ^ 

spines  or 

of  being  t 

poisonous 

tion  of  th 

into  the  w 

])robo8cis 

of  the  pre; 


This  or 
fouml  iu  tl: 
the  connno 
///(/  iu  ma] 
(M'gans,  anc 
is  a  con  vol  1 
<3nd  of  the  ' 

Devvlojnm 
nf  cm  Ilia  and  j 
•■yliiidrical  eil 
Willi  bundles 
find  graduall} 
'orni.  The  ni 
'•'It  shaped  di 
f*trii('(ure  oidy 
iiK't.unorphosif 
i's  (Irst  deacrili 
-'  Usv  niidy  tht 


TYPE  PLATYIIELMINTIIEa. 


167 


3.   Order  Hoplonemertini. 

This  order,  whicli  iudu.les  the  genera  Tetrastemma  and 
Amphporus  nienti.med  above,  has,  like  the  preceding  order 
diluted  funuelH  as  lateral  organs,  and  the  nervous  system  lies 
completely  within  the  muscular  layer  of  the  body-wall  and 
the  nerve-cords  are  united  by  transverse  commissures,  the 
j.loxus  being  wantiug.     The  blood  vascular  system  is  a  closed 
series  of  tubes,  not  communicating  with  lacunar  spaces      The 
most   striking   characteristic  of   the  order  is,  however,   the 
structure  of  the  proboscis,  whic-h  is  armed  near  its  posterior 
(that  IS,  while  invaginated)  end  by  one  or  more  dagger-like 
spines  or  stylets      The  most  posterior  portion  is  not  capable 
ot  l-eing  evaginated,  and  its  walls  are  glandular,  secreting  a 
poisonous  fluid  which  is  poure.l  into  the  more  anterior  por- 
tion of  the  tube,  l,athing  the  stylets  and  thus  being  carried 
into  the  wound  which  n.ay  be  made  by  the  forcibly  evaginated 
IH-oboscis  with  tlie  stylets  coming  into  contact  with  the  body 
ot  tiie  prey  or  enemy,  ^ 


4.  Order  Malacobdellina. 
This  order  contains  a  single  genus,  Mahcohdelln  ,v],ich  is 
found  in  the  mantle-cavity  of  marine  Lamellibranchs,  such  as 
he  common  Mussel  and  Clam.  It  resembles  the  Iloplnncnrr. 
ton  in  many  particulars,  but  is  destitute  of  lateral  ciliated 
organs,  and  its  proboscis  possessos  no  stvlets.  The  intestine 
IS  a  convoluted  tube  without  lateral  dive'rticula,  and  the  hind 
<3nd  of  the  body  is  provided  with  a  sucker. 

Devehpmeutof  the  Nemntiva.~\n  .so.no  Nomortoans.  snch  as  Tetro 

.•y  m,  .,cu    c.hau.,1  larva,  usually  provided  at  the  extremHies  "     2 

.  Lunches  o    U.u^rv  eilia,  whi.-h  n.ay  p,..ssii,Iy  be  sensory  in         en 
nd  gr^u^ually  changes  without  any  .narked  nn.amorphosis  nfo  TZl 
"n...     The  month  <,pons  upon  the  ventral  surface  of'the  body       o 

.TO  o,dy  appearing  nnn.h  later.     In  ,nauy  forn.s.  however,  a  pecu 
"•  ..no  phosis  occurs  during  (he  transformation  of  the  larva  k  ,m   ,       " 
n;  nrst  desc.^,er  an  ^W.  lann,  into  the  adult.     (.„  „.e  ven,;;:;  "l ':;! 
-  -•■•  "'H.y  there  appear  four  invaginationsof  the  octoderm.  two  situate,!  in 


168 


INVERTBBUA  TE  MOltPIIOLCG  7. 


front  of  the  month  and  two  behind  it,  wliicli  gradually  separate  from  the 
ectoderm  to  form  four  single-layered  plates  lying  immediately  beneath  it. 
By  a  subsequent  growth  and  fusion  of  these  plates  a  new  ectodermal  cover- 
ing is  formed  enclosing  the  internal  organs,  and  on  its  completion  the  orig- 
inal larval  ectoderm  is  thrown  off.  In  some  species  a  somewhat  more  com- 
plicated process  occurs.  The  larva,  kuovni  as  the  Pilidium  (Fig.  85),  has 
the  shape  of  a  helmet  from  whose  rim  two  ear-like  lappets  hang  down,  be- 


FlG.  85.  —  IHUdiuni  Lauva  (after  Sai.knsky). 
aj)  =  apical  plate.  m  =  mouth.  h  =  digestive  sac. 

tvveen  which  lic^s  the  mouth-opening  (/«),  while  at  the  ape.\  of  the  helmet 
there  is  an  ectodermal  thickening  («p),  nervous  in  character,  from  whicli 
projects  a  bunch  of  strong  sensory  cilia.  As  in  the  Desor  larva  four  invagi- 
nations of  the  ectoderm  of  the  ventral  surface  occur,  which,  however,  sqia- 
rato  fi-om  the  larval  ectoderm  as  four  hollow  sacs  which  unite  together, 
their  inner  walls  thickening  to  form  the  ectoderm  of  the  young  Nemertcaii. 
while  tiie  outer  walls  iM-conie  thin  and  form  wliat  is  termed  tlie  ainnioii  sur- 
rounding a  cavity  within  which  lies  the  young  worm.  During  the  process 
of  fusion  of  the  four  saes  i  he  entenm  (  S)  and  a  portion  of  the  mesoderiu 
of  the  PHhUum  are  enciosed  and  give  rise  to  the  digestive  tract  and  mcM)- 
denn  of  the  young  worm,  which  later  breaks  through  the  amnion  ami 
I'ilidium  wall  to  become  free. 

Tho  signifk'unce  of  this  metamorphosis  is  decidedly  oKscnre.  Souh' 
authors  regard  it  as  more  jtriniilive  than  the  direct  method  of  developniciii, 
on  the  ground  that  the  I'ifiifiinii  with  its  lappets  presents  general  sinn- 
larities  to  thf  Miiilerian  larva  of  the  I'olyclades  and  is  derived  phylogeiic: 
cally  from  sucli  a  I'orin.  iteing  therefore  more  ancestral  in  its  characNis 
tiian  the  simpler  larva',  ll  must  be  recogni/.tMl,  however,  that  there  is  lU) 
indication  of  mt'laiiiorpliii.^i>  in  llw  I'ulyclad  larviv,  and  furthermore  tliit 


TYPE  PLATYJIELMINTHE8.  169 

the  Nemerteans  perhaps  show  greater  similarilies  to  AUoioccelan  Turbel- 
ana  than  to  Polyclads.  Perhaps  an  exphiuation  of  the  proceL  i  to  be 
found  jn  the  sloughing  of  the  ectoderm  and  the  formation  If  ne"  oil  ated 
col  s  winch  IS  seen  in  the  larva  of  a  Pal.Tonen.ertean,  C>.Ma/o^/.V,  he 
motamorphos,s  o  Desor's  larva  and  of  the  P///.//.,.  being  a  greater  a.ni 
more  complicated  ecdysis  derived  from  the  simpler  one 

Some  niteresling  evidence  as  to  the  morphological  significance  of  tho 
anus  ,.s  to  be  derived  from  a  study  of  its  devLopm^nt  in  X  Nemer    i' 
I   ,.  un  open.ng  which  has  been  considered  by  some  to  have  arisen  bvi; 
closure  m  the  nuddle  of  an  elongated  slit-like  blastopore-the  two  en  L  hot 
ever,  remammg  open  to  form  respectively  the  mouth  and  anus-  and  it  h.s 
been  thought  that  the  direct  transforn.ation  of  the  blastopore    ntotlpt 
maneu,  mouth  in  some  case.,  and  in  others  into  the  permanent  am 
receives  on  this  theory  an  explanation.     The  phenomenon  of  the     osu     of 
tl  0  blastopore  ,n  the  middle  does  actually  occur  in  the  Annelid-like  TrI 

0  eate  Per,pat,,s  and  in  many  forn.s  both  mouth  and  anus  stand  in  cbe 
outogenetic  relationship  to  the  blastopore.     In  th.,  Nemerteans  are  reme 
sented  the  most  lowly  organised  animals  which  possess  ..oth  i.;::i  tl  la  ml" 
anus  and  accord.ngly  it  might  be  expected  that  in  them  the  original  rela 
no-'''l«  wdl   be  n.ost  clearly  seen.     The  young  Nen.ertean  pots      e    no 
.  "US.     t  resembles,  so  tar  as  its  digestive  tract  is  concern,.,!,  an  Alloioco^l-.r 

1  .s  only  relatively  very  late  in  its  life-history  that  the  anus  app,  "      mi 
HM.  in  a  region  of  the  body  which  has  no  relation  whatever  to   he    riinn 

bia.s.opore.  This  fact  .shouhl  carry  considerable  weignt  w  t  lisp  en  v 
asm  the  „u,,>rity  of  forn.s  the  anus  is,  in  co.npait.n  with  ,  .^ m  u^ 
of  cativey  late  formation.     It  seems  not  improbable  that  primitive; 

UK'}  ai,'  entn-ely  secondiiry. 

The  in.lieation  ,>f  m,.tau>erism  .seen  in  the  Nemerteans  n.n.ls  no  f„rtl„.r 
discussion  aff.r  what  has  been  said  on  p.  43  with  reference  to  similar     'ci 
lanties  m  the  Turbellarians.  ' 


I 


Sli|iKlN«D()M   MiyPAZOA. 
TYPE  PLATYllHl..\riXriIES. 

I.  Cla.ss  TrunKiXAi«A.-Eet,)d,.rm  eiliat,.,!;  no  anal  openiuK 

2"    tw  ';;;■':'  -^'•""^'I-eM.nt,  but  n..  .iigestiv,-  tra,.t;    Co>n.n.ta^ 

2.  (>.de.l/A.o,,Wa.-I),geslive  tract  pre.s..nt;  space  betu.Hw,  it  and 

s    Jf"'-^-;;,"'  "^^''I'H-.ll.y  parenchyma.     M.„nt„s,  Pl,n,i„s,n,n„ 

8.  Or,l,.r   /^.,/./o,.,W,,._I)igestive   tract   straight    rod-    .,r  .sae-Mke- 

simce  between   it  an,l   bo-ly^wall  n.>t   till,-,!  with  parencl.vma' 

Mu'.n>Htoma,  Misostama,  Prorhy„rh„.s,   Vorte, 

4.  Or,ler  '/VA7«,/m.-l)iges,iv.>  tract  branched,  three  principal  limb« 

mm  nso  to  8econ,h.ry  branclu-s:  mnio  and  femJe  repin  hot   ^ 


170 


INVERTEBRATE  MORPHOLOGY. 


organs  with  common  opening.     Gunda,  Playiaria,  Phagocata, 
Dendrocoslum,  Bdelloura,  Bipalium,  Syncoelidium. 
5.  Order  i^/ycZadeo.— Digestive  tract  branched,  tlie  primary  branches 
being  numerous;  male  and  female  organs  having  separate  open- 
ings. 

(a)  With  terminal  sucker  (Co^yZea).    Thysamzoon,  Eurylepta, 

(b)  Without  sucker  (Acotylea).     Planocera,  Leptoplana,  i^ty- 

lochus. 
IL  Class  Trematoda.— Ecto-  or  endoparasites;    ectoderm  not  ciliated; 
with  digestive  tract  and  suckers. 

1.  Order  Poly stomea.— Suckers  more  than  two;  development  direct; 

usually  ectoparasites.     Polystomum,  Sphyramira,  Tristomum] 
Gyrodactylus. 

2,  Order  i>j*i!omecE.— Suckers  one  or  two;  development  indirect;  usu- 

ally endoparasitic.     Distomum,  Monostomnm. 

III.  Class  Cestoda.— Endoparasites;  ectoderm  without  cilia;  no  digestive 

tract  or  mouth;  usually  strobilated.     Tit7iia,  Bothriocephaliis, 
Caryophyllmis,  Liyula,  Trianophonis,  Archigetes. 

IV.  Class  Nemeutina.— Ectoderm  ciliated;   not  parasitic;  anus  present; 

with  protrusible  proboscis. 

1.  Order  Palmmemertini.—l^iGv&l  ciliated  funnels  shallow;  nervous 

system  imbedded  in  ectoderm;  proboscis  without  stylets.     Cari- 
nella. 

2.  Order  ScJuzonemertfni.—Lnteriil  ciliated  funnels  deep;  nervous 

system  imbedded  in   muscle-layer;   proboscis  without  stylets. 

Cerebratulus. 
Order  Hoptonemertini.— Lateral  ciliated  funnels  deep;   nervous 

system   within    muscle-layer;    proboscis   with   stylets.      Tetra- 

stemma,  Ainphiporus, 
Order  MafacobdeUiua.—'No  lateral    ciliated    funnels;   proboscis 

without  stylets.     Mnlocohdella. 


8. 


B 

leuokan 

Heidel 

A. 

Lang. 

Nerven 

tion  zu 

C. 

Clang.    ., 

wurmkt 

W 

c.  Helm 

London 

0. 

Bttrger. 

Monogr 

LITERATURE. 


TrilBELLAniA. 

I  vonOraflf.     Monographie  der  Turhellarien  :  \.  Rhnhdoewliden.  Leipzig,  188:' 

L.  von  Graff.     Die  Orgatnmtioii  der  Tiirhellaria  tirrdn.     Leipzig,  1891. 

L.  BJJhmig.      Uiitersitchutigen  iihrr  r/inbdocwkn  Turbellarien,  H.     Zeitscbr.  fur 

wissciisrli.  Zoologie,  i,F,  1890. 
W.  M.  Woodworth.     Confvihiifions  to  the  Morphology  of  the  Turbelluria,  I.    Bui- 

Ictin  of  tbo  Muspiim  of  Comp.  Zool.,  xxi,  1891. 
A.  Lang.     Die  Po/yrl,id,n,     Fauna  w.  Florn  des  (ilolfe.s  von  iSeapel.     MonoLT 

XI,  1HH4. 

W.  M.  Wheeler.     Synrolidiim  pellneidum,  a  new  marine  Tridad.    Jour,  of 
Morphology,  IX,  1894. 


TYPE  PLATYHELMINTHE8. 

THEMATODA  AND  CE8TODA. 


171 


B.  leuokart.     Die  Parasiten  dea  Memchen.    2te  Aufl    Bd    T      ^^^^  • 

Heidelberg,  1879-1889.  -^ipzig  u. 

A.  Lang.  f^«««,.««cAM«^,„  g«^  vergleichenden  Anatomie  nnd  Hiatoloai.  d.. 
Ner^ensystems  der  Turbellarien.  II  u.  III.  Mittheilunrn  a  d  ZcTsfr 
tion  zu  Neapel,  ii   1881  """ocn  a.  a.  IacoI.  Sta^ 

NEMERTINA. 


§ 
5 


4m  I 


172 


mVEHTEBRATE  MOHFEOLOOT. 


CHAPTER  VIII. 


TYPE  NEMATHELMINTHES. 

The  Nemathelmiuths  are,  like  the  members  of  the  preced- 
ing type,  characterized  by  the  form  of  the  body,  which  is 
cylindrical  and  usually  elongated  or  even  thread-like,  Avhence 
the   popular   terms   Round-worms    or  Thread-worms   which 
are  frequently  applied  to  the  hi.     The  ectoderm  is  covered  by 
a  thick  layer  of  cnticle  which  it  secretes,  and  in  counectiou 
with  which  spines,  bristles,  or  hooks  may  be  developed  at 
various  parts  of  the  body.     There  is  no  trace  of  segmentation 
or  reduplication  of  orgru^;,  with  the  exception  that  in  some 
forms  the  circular  nerve-commissures  uniting  the  longitudinal 
cords  may  succeed  each  other  with  tolerable  regularity  ;  the 
cuticle,  it  is  true,  especially  when  taick,  is  ringed  by  numer- 
ous grooves  succeeding  one  another  at  short  intervals,  l)ut 
this  cannot  be  interpreted  as  an  indication  of  metamerism, 
but  is  more  probably  a  provision  to  counteract  the  rigidity  of 
the  cuticle  and  to  give  a  considerable  amount  of  mobility  to 
the  body.     The  Nemathelmiuths  accordingly  have  the  same 
grade  of  individuality  as  a  simple  Platyhelminth,  such  us  un 
Alloiocoelan,  and  are  to  be  regarded  as  metaiuere  iiuiividuals. 
One  important  ditierence  of  structure  which  these  worms 
show  from  the  Platyhelininths  is  the  presence  of  a  capacious 
coelom,  the  interval  between  the  digestive  tract  and  the  mus- 
culature of  the  body- wall  not  being  tilled  up  by  parenchyma- 
tous mesoderm,  but  being  a  sim})le  undivided  cavity  in  which 
lie   the   reproductive   orgnus.     These  latter  are  simple,  the 
animals  being  as  a  rule  bisexual,  and  there  is  no  separation 
of  the  female  organ   into  ovary  and  vitellarium.     Structures 
of  an  excretory  nature  occur  in  one  of  the  two  classes  into 
which  the  type  is  divisible,  but  a  blood  vascular  system  is 
entirely  wanting. 

The  lial)it  of  life  varies  greatly  in  the  various  members  ..1' 


TYPE  NEMATIIELMINTHE8. 


173 


the  group.  In  the  class  Nematoda  many  forms  live  freely  in 
the  sea,  fresh  water,  or  damp  earth,  while  others  are  parasitic 
during  a  part  of  their  lives,  and  others  again  are  parasites 
practically  throughout  their  whole  existence.  The  Acantho- 
cephala  aro  without  exception  parasitic. 

I.  Class  Nematoda. 

The  Nematodes  are  distinguished  from  the  members  of 
the  second  class  by  the  presence  in  nearly  all  cases  of  a  dis- 
tinct digestive  tract,  usually  with  mouth  and  anus,  and  by 
the  absence  of  a  retractile  proboscis  furnished  with  hooks 
at  the  anterior  end  of  the  body.  The  arrangement  of  the 
muscles  of  the  body-wall  are  also  peculiar  inasmuch  as  longi- 
tudinal muscles  only  are  present  (Fig.  86,  m),  which  iustead"of 
forming  a  closed  sheath  are  interrupted  along  four  longitudi- 


Fio.  8G.— TuANRVEKSE  SECTION  OP  Amir>\i  Inmhricoides  at  the  Lkvkl  of 

PlIAUYNX  (from  HEHTWKi). 
c  =  cuticle.  m  =  loiigitudiuiil  muscles. 

d  =  dorsal  line.  s  =  latenil  line. 

?i  =  hypodeimis.  v  =  vcutriil  Hue. 

to  =  utpbridiuni. 

nal  lines  {d,  v  and  .<?),  or  in  some  cases  aloug  a  siugle  ventral 
line,  in  the  former  case  there  being  four  longitudinal  bundles 
of  muscles  extending  the  length  of  the  body.  In  the  stnu'- 
tiire  of  most  of  the  organs,  however,  considerable  variation  is 
found,  and  it  will   be   most  convenif^nt  to  describe  them   as 


I 


i 


174 


INVERTEBRATE  MORPHOLOOT. 


m 


they  are  found  in  each  of  the  two  orders  into  which  the  class 
may  be  divided. 

1.  Order  Eunematoda. 

This  order  contains  the  majority  of  the  Nematoda,  and 
all  Its  members  are  furnished  with  a  mouth  and  anus  and  a 
functional  digestive  tract.     The  mouth  is  iu 
some  cases  at   the   bottom   of  a  funnel-like 
depression  which  may  be  armed  with  spines 
special  developments  of  the  cuticula  which 
covers  the  body.     This  is  throughout  cylin- 
drical  in  shape,  except  that  in  the  males  of 
some  species  it  expands  at  the  posterior  ex- 
tremity into  a  relatively  large  funnel-shaped 
structure  with  thin  walls,  the  bursa  (Fig.  87), 
at  the  bottom  of  which  lies  the  opening  of  the 
cloaca,  a  cavity  into  wliich  the  intestine  and 
the  male  reproductive  organ  open.     Beneath 
the   ringed   cuticle   lies  the  ectoderm  (hypo- 
dermis)  which  secretes   it,  and  beneath  this 
the   muscular  layer   which   consists  only  of 
longitudinal  muscle-fibres,  differentiations  of 
the  outer  ends  of  large  cells  whose  uudiffer. 
entiated  inner  ends  project  into  the  coelom,  so 
as  almost  to  obliterate  it  in  some  cases.     The 
muscle-fibres  do   not,  however,  form  a  com- 
plete   continuous    sheath    surrounding    the 
ccelom,  but  are  interrupted  along  four  longi- 
F.o.  87.  -  Aacaris  ^^^^^^^l   lines,    two   lateral,    one  dorsal,    and 
nigrovenosaUKi.^  o"e  ventral  (Fig.  86).     The   ccelom  contains 
(after  LEircKAKT).      the  intestine  and  reproductive   organs,  and 
is  peculiar  iu  that  it  is  not   bounded    by  a 
limiting    cellular    membrane    or    peritoneal 
lining,  being  simply  a  space  comparable  tc> 
tlie  coelomic  cavities  of  the  Rhabdocoela  or 
the  blood-sinuses  of  the  Nemerteaus. 

The  digestive  tract  is  a  straight  tube  traversing  the  bodv 
from  one  extremity  to  the  other,  opening  posteriorly  in  thi 


sp 


i  =  intestine. 
p?i  =  pharynx 
sp  =  spicules. 
te  =  testis. 


female 

commor 

anterior 

rectly  c( 

while  pc 

Jayer  of 

cular  tia 

The 

appears 

lining  hj 

in  the  tli 

terior  p( 

which  o] 

behind  t 

This 

the  ante] 

ganglion 

one  of  w 

other,  w] 

median  ' 

nerve-rin 

the  dorss 

backwar( 

nect  the 

body  not 

not  sue^g( 

commissi 

are  as  a  i 

The  r. 

male  the^ 

in  its  up] 

dilating  1 

short  ejac 

of  this  la 

small  sac 

ble  of  bei 

with  the  1 

the  other 

which  dih 


TYPE  NEMATHELMINTHES. 


176 


female  directly  to  the  exterior,  in  the  males  into  a  cloaxia 
common  to  it  and  to  the  male  organ  of  reproduction.  Its 
anterior  part  is  a  muscular  oesophagus  lined  with  cuticle  di- 
rectly continuous  with  that  covering  the  surface  of  the  body, 
while  posteriorly  it  is  a  delicate  tube  composed  of  a  single 
layer  of  cells,  not  being  surrounded  by  any  mesodermal  mus- 
cular tissue. 

The  excretory  system  is  not  as  yet  fully  understood.  It 
appears  to  consist  of  a  pair  of  tubes,  for  which  no  cellular 
lining  has  as  yet  been  made  out,  which  lie,  one  on  each  side, 
in  the  thickened  hypodermis  of  the  lateral  lines.  In  the  an- 
terior portion  of  the  body  they  unite  to  form  a  single  tube 
which  opens  to  the  exterior  in  the  median  ventral  line  not  far 
behind  the  brain  (Fig.  88,  B). 

This  latter  ^jonsists  of  a  ring  or  nerve-collar  surrounding 
the  anterior  part  of  the  oesophagus  on  which  lateral  masses  of 
ganglion-cells  occur  and  which  gives  rise  to  two  main  nerves, 
one  of  which  runs  back  in  the  median  dorsal  line,  while  the 
other,  which  in  some  forms  appears  to  be  double,  lies  in  the 
median  ventral  line.  Other  nerves  pass  forwards  from  the 
nerve-ring  to  the  anterior  part  of  the  body,  and  in  addition  to 
the  dorsal  and  ventral  nerve-cords  two  lateral  nerves  pass 
backwards  a  short  distance,  while  circular  commissures  con- 
Dect  the  two  main  nerve-cords,  those  of  the  two  sides  of  the 
body  not,  however,  being  opposite  each  other,  so  that  they  do 
not  sue^gest  a  pseudo-metamerism  so  strongly  as  the  similar 
commissures  of  the  Hoplonemertini.  Special  sense-organs 
are  as  a  rule  absent,  though  a  few  forms  possess  eyes. 

The  reproductive  organs  are  exceedingly  simple.  In  the 
male  they  are  represented  by  a  single  convoluted  tube,  lined 
m  its  upper  part  by  the  mother-cells  of  the  spermatozoa  and 
dilating  below  into  a  seminal  vesicle,  to  which  succeeds  a 
short  ejaculatory  duct  which  opens  into  the  cloaca.  The  walls 
of  this  latter  cavity  are  frequently  invaginated  to  form  two 
small  sacs  in  each  of  which  lies  a  chitinous  spicule  capa- 
ble of  being  protruded  from  the  cloacal  opening  and  serving, 
with  the  bursa,  as  copulatory  organs.  The  female  organs,  on 
the  other  hand,  consist  of  a  pair  of  convoluted  tubes,  each  of 
which  dilates  into  a  uterus  and  unites  with  its  fellow  to  form  a 


i 


I 


176 


INVEHTEBliATE  MOIiPUOLOG Y. 


single  tube,  tbe  vagina,  sometimes  with  muscular  walls,  which 
opens  to  the  exterior  in  tlie  ventral  mid-line  some  distance  in 
front  of  the  anus.  As  a  rule  the  sexes  are  separate,  her- 
maphroditism occurring  only  in  a  few  isolated  cases. 

Many  Nematodes  are  free  throughout  their  entire  exist- 
ence, living  in  the  sea,  fresh  water,  or  damp  earth,  and  fre- 
quently possessing  eyes.  Others  are  found  in  some  domestic 
products,  such  as  the  viuegar-eel  {Anguillula),  found  in  vine- 
gar and  sour  paste  ;  Avhile  others,  again,  are  parasitic  on 
plants,  such  as  Tylenclms,  which  lives  upon  the  young  grains 
of  wheat  and  hi  some  cases  produces  very  rerious  damage  to 
crops,  and  Heterodera,  which  is  quite  as  injurious  to  root- 
crops.  More  interesting,  however,  are  a  number  of  forms 
occurring  as  parasites  in  animals,  many  affecting  man,  in  some 
cases  producing  serious  results. 

Life-histories  of  the  Eunematoda.—Tha  f  uving  forms  show  no 
peculiarities  of  development,  the  immature  a.  I'liai  developing  directly 
from  the  egg.  Among  the  parasitic  forms,  howev  interesting  variations 
from  direct  development,  due  to  a  change  of  host,  occur,  a  wel'.-markod 
lieterogony  occasionally  being  found.  An  example  of  this  is  seen  in  lihah- 
ditis  iii;/i-ovenosa,  which  at  one  stage  of  its  existence  lives  in  damp  earth, 
the  females  being  viviparous  and  producing  young  which  make  their  way 
iuto  the  lungs  of  frogs,  where  they  assume  a  form  which  led  them  to  be 
assigned  to  the  genus  Ascan's,  and  where  tliey  become  mature.  At  this 
stage  tiiey  differ  from  the  Rhabditis  forms  in  being  hermaphrodites,  and 
from  the  eggs  deposited  by  them  the  Rhabditis  generation  again  results. 

From  a  medical  standpoint  one  of  the  most  important  forms  is  Trieli/iia 
spiralis,  which  occurs  enc^psuled  in  the  muscles  of  various  warm-blooded 
animals,  such  as  man,  the  pig,  rat,  mou.se,  and  occasionally  in  the  fox,  cat, 
and  ral)bit.      Tiie  capsules  are  oval  and  about  0.6  mm.  in  length,  and  occa- 
sionally have  a  white  color,  due  to  the  deposition  of  calcareous  matter  in 
the  wall.     In   tlie  interior  of  the  capsule  lies   coiled   up  an   iminatu)'(! 
Trichina,  which  may  retam  its  vitality  in  tliis  condition  apparently  during 
the  lifetime  of  its  host.     Should,  for  instance,  improperly  cooked  or  sahcd 
pork  which  contains  such  capsules  Ijc  eaten  l)y  man.  tlio  capsule  becomes 
dis.solved  by  the  digestive  juices  and  the  young  Trichina  is  .set  free  in  the 
small  intestine  and  in  tlie  course  of  a  few  days  becomes  sexually  matuiv. 
The  males  die  shortly  after  having  reached  maturity,  but  the  femali's 
l)()re  into  tlio  intestinal  walls,  some  i)assing  through  into  the  mesentery, 
where  tliey  may  contimie  to  exist  for  several  weeks.     They  are  viviparous 
and  <'acii  individual  may  produce  as  many  as  10.000  young,  whieli  make 
their  way  to  the  voluntary  nniscles.  especially  to  those  of  the  neck  and  to 


the  diaphi 

active  mi; 

about  0.01 

tiiey  prod 

reached  tl 

cysts  mea 

they  prodi 

capsuled  : 

though  th 

Other  1 

worm  (Fij 

length  anc 

an  earth-M 

inhabits  tl 

(Fig.  88), 

anterior  h 

the  in  test 

slender   p 

tion  hang 

intestine. 

forms  ma 

of  tlie   til 

their  ova, 

fer  very  g 

developme 

there  is  ik 

are  tjikc-n 

I'er.sonal 

drinking-\ 

In  add 

been  ment 

more  espe 

mates.      Z 

form  about 

teeth  or  bl 

which   fast 

■small  intes 

of  its  host 

develop  in 

and  probat 

t'ected.     It 

known  as  ( 

tunnels,  ha 

tunnel,  whe 

workers  in 

is  a  very  sh 


TTPE  NEMATEELMINTHES. 


177 


tlie  diai»hragm,  partly  by  the  lymphatic  and  blood  vessels,  and  partly  by 
active  migration  in  the  connective  tissue.  The  young  Trichince  measure 
about  0.01  mm.,  and  duiinjr  their  i)assage  into  the  substance  of  the  mu.scles 
tiicy  prodi  more  or  less  .severe  inrtaniinatory  disturbances.  Having 
reached  the  muscle  tissue  they  become  encysted  therein  (Fig.  89,  A),  the 
cysts  measuring  about  0.4  mm.  in  length,  and  if  the  disturbances  which 
they  produce  have  not  proved  fatal  to  the  host  the  danger  is  past,  the  en- 
capsuled  Trichina  undergoing  no  further  development  within  this  host, 
tliough  they  may  retain  (heir  vitality  for  many  years. 

Other  forms  which  o.  ir  in  man  are  Ascaris  lumhricoides,  the  round- 
worm (Fig.  88,  B),  a  large  form,  of  which  the  female  measures  40  cm.  in 
Icnglh  and  the  male  25  cm.,  and  which  bears  some  resemblance  in  shape  to 
an  earth-worm,  Oxyurisvermiculans,  asmaller  form,  1  cm.  in  length,  which 
inhabits  the  rectumespecially  of  young  children,  and  Trichocephaiusdispar 
(Fig.  88),  which  measures  3-5  cm.  in  length  and  is  characterized  by  the 
anterior  half  of  the  body  being  exceedingly  slender,  the  worm  boring  into 
the  intestinal  wall,  especially  in  the  neighboihood  of  the  caecum,  by  this 
slender  portion,  the  hinder  thicker  por- 
tion hanging  freely  in  the  wall  of  the 
intestine.  The  presence  of  these  three 
forms  may  be  recognized,  independently 
of  the  finding  of  the  actual  worm,  by 
tlieir  ova,  whose  respective  characters  dif- 
fer very  greatly.  So  far  as  is  known  the 
development  of  these  forms  is  direct  and 
there  is  no  intermediate  host,  but  the  ova 
are  tjikc-n  into  the  body  with  the  food. 
I'cr.sonal  uneleanliiiess  and  imperfect 
drinking-water  may  be  causes  of  infection. 

In  addition   to  the  forms  which  have 
t)een  mentioned  there  arc  a  few  which  are 
more  especially  frc(iuent  in   tropical  cli- 
mates.     ^ocAm/,.sw/«o</r.m7/.  is  a  s.uall  Fio.   m.-A,   7'nV/./«7."m.vsled 
torm  about  1-3  cm.  in  length,  with  strung      iu  ,„„.s,.!e;  B,  amerior  exirem- 


iiy  of  Aiscaris  lumbricoidts 
fiom  the  veulral  sui  face,  show- 
ing ilie  two  ventral  oral  papiilaj 
and  the  excretory  pore  o.oili 
.■ifterLKTOKAiiT);  C,  Trichoceph' 
alus  dispar  (after  Owen). 


teeth  or  blunt  sj)ines  in  the  mouth  region, 

which  fastens   itself  to  the   wall  of  the 

■small  intestine  and  lives  upon  the  blood 

nf  its  host,  producing  an;i'iuia.     Its  ova 

develop  in  stagnant  water  or  damp  earth, 

and  probably   man   becomes  directly   in- 

jVcted.     It  has  long  been  known  in  the    tropics,  producing  the  disease 

known  as  Chlorosis  mjyptiaea,  but  may  also  affect  miners  or  workers  in 

tunnels,  having  appeared  endenucally  in  the  workers  ou  the  ."'t  Gotliard 

tunnel,  whence  it  lias  since  spreac'  somewhat  in  Germany,  especially  among 

workers  in  clay.     Filariu  inedinensis  is  limited  entirely  to  the  tropics  and 

IS  a  very  slender  worm  ne/irly  1  metre  in  !en-lh  which  lives  in  the  conuec 


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178 


INVERTEBRATE  MORPHOLOGY. 


tive  tissue  beneath  the  skin,  producing  ulcers,  at  the  bottom  of  which  tha 
worm  lies  coiled  up.  The  ova  develop  in  water  and  the  embryos  pass 
probably  into  small  Crustacea,  which  are  swallowed  with  drinking-water. 
Mlaria  sanguinis  hominis,  also  solely  tropical  in  its  distribution, 
receives  its  name  from  the  fact  that  it  lays  its  ova  in  the  blood  of  mm, 
which  may  thus  swarm  with  countless  numbers  of  small  worms.  These 
make  their  way  to  the  exterior  of  the  body  by  the  kidneys,  producing 
hemorrhages  or  minute  abscesses  in  that  organ  and,  as' the  result  of 
these,  milky  or  bloody  urine. 


2.  Order  Oordiacea. 

This  order  includes  the  families  of  the  Gordiidce  and  Mer. 
mithidcE,  long  slender  thread-like  worms,  which  differ  from  the 
Eunematoda  in  several  important  respects.  They  occur  in 
their  mature  state  iu  fresh  water ;  in  their  immature  stages, 
however,  they  are  parasitic  in  insects.  In  the  adult  Gordhis 
the  mouth  is  usually  closed  by  an  overgrowth  of  the  cuticle, 
and  the  anus  is  lacking  iu  Mermis.  The  musculature  of  the 
body- wall  consists  only  of  longitudinal  fibres  (Fig.  89,  m),  which 


11 


Fio.  89.— Tkansverse  Section  or  Oordius  (after  Vwdovbkt). 


eu  =  cuticle. 
d  =  intestine. 
Ay  =  iiypotlennis. 
ff»  =  longitudinal  muscles. 

OP  =  oviduct. 


me  =  mesentery. 

n  =  nerve-cord. 

p  =  peritoneum. 
ut  =  uterus. 


differ  in  their  I'rraugement  from  those  of  the  Eunematoda  in 
being  interrupted  only  in  the  mid-ventral  line.  The  c(»lom 
is  lined  by  a  peritonea)  epithelium  (p)  lying  beneath  the 


TYPE  NEMATHELMINTHES. 


179 


iP'^ 


muscle-cells,  and  is  divided  into  two  lateral  chambers  by  a 
mesentery  (me)  running  the  entire  length  of  the  body  and  con- 
sisting of  two  layers  surrounding  the  intestine  (d),  and  inserted 
into  the  body-wall  dorsally  and  ventrally,  their  outer  surfaces 
being  lined  by  a  continuation  upon  them  of  the  peritoneal 
epithelium. 

No  excretory  system  has  been  as  yet  discovered.  The 
nervous  system  consists  of  a  ganglionic  ring  surrounding  the 
oesophagus,  from  which  a  number  of  nerves  pass  forward, 
while  a  single  nerve-cord  (w)  passes  backwards  in  the  mid- 
ventral  line,  dilatiiig  at  the  posterior  end  of  the  body  into 
a  ganglionic  mass. 

The  reproductive  organs  consist  in  the  female  of  a  series 
of  ovaries  {ov)  attached  one  behind  the  other  to  each  mesen- 
tery above  the  intestine.  In  the  mesenteries  two  tubes  (ut) 
pass  backwards  which  receive  some  of  the  ova  and  function 
as  uteri,  near  the  hind  end  of  the  body  bending  ventrally  to 
open  into  the  cloaca,  whose  wall  is  invaginated  to  form  a 
single  seminal  receptacle.  The  testes  have  not  yet  been 
found,  but  two  seminal  vesicles,  corresponding  to  the  uteri  of 
the  female,  occur  and  open  likewise  into  the  cloaca,  which  in 
the  male  is  evertible  and  serves  as  a  copulatory  organ. 

The  Affinities  of  the  Nematodes. — Tlie  relaiionshipsof  the  Nematodes  are 
exceedingly  obscure.  Their  unsegmented  character  and  the  character  of 
the  nervous  system  seem  to  ally  them  more  closely  with  the  Platyhelminths 
than  with  higher  forms,  but  the  relationships  to  any  of  the  known  Platy- 
helminths must  be  exceedingly  remote.  The  parasitism  which  occurs  so 
frequently  in  the  group  is  to  be  considered  as  secondary,  since  so  many 
forms  lead  a  free  life  and  peculiarities  of  structure  can  hardly  be  attributed 
to  degeneration.  The  Gordiacea  stand  on  a  Higher  plane  than  the  Eu- 
nematoda,  as  shown  by  the  possession  of  a  mesentery  and  the  arrange- 
ment of  the  reproductive  organs  and  nervous  system,  which  Iwjar  some  sim- 
iliirities  to  those  of  the  Annelids,  but  their  Nematode  eharacteristies  uro 
must  pronounced.  Perhaps  the  ancestors  of  the  Nematodes  are  to  bo  fountl 
in  the  yet  unknown  intermediate  forms  between  the  Platyhelminths  and 
Annelids,  a  view  which  would  account  for  their  similarities  in  cortaiu 
respects  to  both  these  groups. 

II.  Class  Acanthocefhala. 

This  class  contains  a  number  of  })arHBitic  forms  which 
occur  more  especially  in  thu  digestive  tract  of  tishes,  though 


to 


180 


IN  VERTEBRA  TE  MORPHOLOQ  Y. 


lit 


rm 


^ 
<« 


also  found  in  Mammalia  and  in  exceptional  cases  in  man.  A 
great  uniformity  of  structure  exists  thvoughout  all  the  species, 
so  that  they  are  all  referable  to  a  single  genus,  Echimrhynclms. 
The  body  (Fig.  90)  is  cylindrical  and  as  a  rule  not  very  long, 

and    a    marked   distinction   froni   the 
-Nematodes  is  found  in  the  retractile 
proboscis  {pr)  occurring  at  the  anterior 
end  of  the  body.     It  is  a  cylindrical 
prolongation  of  the  anterior  portion  of 
the  body  and  is  provided  M'ith  a  number 
of  chitinous  hooks  by  means  of  which 
it  adheres  to  the  intestinal  wall  of  its 
host.     The   proboscis   may  be  invagi- 
nated  into  a  double- walled  muscular 
proboscis-sheath  by  whose  contraction 
it  may  again   be  protruded,  a  strong 
retractor   muscle,  extending  from  the 
tip  of  the  proboscis  to  the  base  of  the 
sheatli,  serving  for  the  invagination  ; 
and  from   the  base  of  the  sheath  re- 
tractor muscles  {rm)  pass  to  the  body- 
walls  and  serve  to  hold  the  sheath  in 
position.     No  traces  of  a  digestive  tract 
occur. 

The  body  is  covered  upon  the  out- 
side by  a  thick  cuticle  secreted  by  the 
subjacent  hypodermis,  which  is  a  rather 
Fig.  00. -Male  Echinarhyn-  thick  layer  consisting  of  a  protoplasmic 
'  niatiix  in  which  nuclei  are  scattered 
but  in  which  no  cell-outlines  are  to  be 
distinguished.  Beneath  the  cuticle  the 
matrix  has  a  fibrillar  character,  and 
near  its  inner  surface  it  is  hollowed  out 
into  a  network  of  anastomosing  canals 
of  which  mention  will  be  made  later. 
Beneath  the  hypodermis  lies  a  basement-membrane  within 
which  are  Uvo  layers  of  muscle-cells,  having  the  same  ei.i- 
thoho-muscular  character  as  those  of  the  Nematodes,  the 
fibres  of  the  external  layer  having  a  circular  direction,  while 


g  -  glands 

I  =  leiuiiisciis 

p  =  pt'uis. 
pg  =  proboscis  ganglion 
pr  ■=  proboscis. 
nn  —  retractor  muscle. 

t  =  testis. 


TYPE  NEMATUELMINTHE8. 


181 


those  of  the  iuuer  layer  have  a  lougitudiual  course.  The 
body-wall  encloses  a  well-marked  coelom,  not  liued  by  a 
special  peritoneal  epithelium,  but  which  contains  the  repro- 
ductive  organs  and  is  traversed  by  the  retractor  muscles  of 
the  proboscis-sheath. 

The  nervous  system  consists  of  a  ganglionic  mass  {pg) 
lying  within  the  proboscis-sheath  which  sends  forward  nerves 
for  the  supply  of  the  walls  of  the  sheath  and  -^f  the  retractor 
muscle  of  the  proboscis.  Posteriorly  two  lateral  nerve-cords 
extend  backwards  along  the  sides  of  the  body,  and  in  male 
individuals  are  connected  near  the  posterior  extremity  with  a 
ganglion  lying  beneath  the  reproductive  ducts  and  from  which 
nerves  pass  to  the  genital  apparatus. 

The  system  of  lacunar  canals  which  form  a  network  in  the 
lower  layers  of  the  hypodermis  is  probably  excretory  in 
function.  The  canals  are  found  throughout  the  entire  hvpo- 
dermis,  both  in  the  proboscis  and  f,  the  body-wall,  in' the 
latter  there  being  indications  of  two  larger  lateral  trunks. 
From  the  point  of  junction  of  the  proboscis  with  the  body- 
wall  two  muscular  sacs,  the  lemnisci  (l) ,  hang  down  into  the 
ccelom.  The  cavity  which  they  contain  commun.cates  with  a 
circular  lacuna  which  surrounds  the  base  of  the  proboscis 
and  with  which  the  lacuntc  of  the  proboscis-hypodermis  like- 
wise communicate,  this  system  of  the  proboscis-lacuna)  and 
the  lemnisci  being  shut  off  from  the  system  of  the  body-wall 
by  a  partition  extending  from  the  basement-membrane  to  the 
cuticle.  The  lemnisci  have  been  regarded  as  possible  repre- 
sentatives of  a  digestive  tract,  but  it  seems  more  probable 
that  they  are  reservoirs  for  the  reception  of  the  fluid  con- 
tained in  the  lacunro  of  the  proboscis  when  it  is  driven  from 
them  during  invagination. 

The  reproductive  organs  are  much  more  complicated  than 
those  of  the  Nematodes.  The  sexes  are  separate,  the  male 
individuals  being  usually  smaller  than  the  females.  Tlie 
ovaries  are  paired  bodies  enclosed  within  a  muscular  Ugnment 
attached  anteriorly  to  the  base  of  the  proboscis-sheath  and 
posteriorly  to  the  reproductive  duct.  At  an  early  stage  of 
their  development,  however,  the  ovaries  split  up  into  masses 
which  float  about  in  the  coelom  together  with  large  numbers 


182 


IN  VERTEBRA  TE  MORPHOLOO  Y. 


of  separated  ova.  They  pass  to  the  exterior  by  a  complicated 
system  of  ducts,  the  most  anterior  portion  of  which  is  a  wid& 
funnel-shaped  structure,  the  hell,  to  whose  wall  the  ligament  i» 
attached  and  which,  by  a  rhythmical  expatjsion  and  contrac- 
tion, engulfs  the  ova  and  ova-masses  floating  about  in  the 
cob'om.  From  the  lower  end  of  the  bell  they  escape,  the  ova- 
3e8  to  be  returned  to  the  coelom,  while  the  fertilized  sepa- 
rate ova  pass  into  a  short  tube,  the  ovUmt,  which  opens  below 
into  a  muscular  uterus,  which  finally  communicates  with  the 
exterior  at  the  posterior  end  of  the  body. 

The  male  apparatus  consists  of  usually  two  testes  (Fig 
90,  t)  enclosed  within  the  ligament,  which  is  attached  below 
to  the  wall  of  the  evertible  bursa.  From  each  testis  a  duct 
passes  backwards,  the  two  soon  uniting  to  the  single  vas  de- 
ferens winch,  after  receiving  the  ducts  of  some  unicellular 
glands  {gl),  opens  into  the  bursa  at  the  tip  of  a  muscular  penis 
(p).  The  bursa  when  everted  is  a  somewhat  funnel-shaped 
structure  at  the  bottom  of  which  is  the  penis,  the  edge  being 
furnished  in  some  forms  with  hooks  by  means  of  which  it 
serves  as  a  copulatory  organ. 

The  life-history  of  the  Acanthocephala  includes  a  change  of  host  The 
arv8B  are  found  in  the  body-cavity  of  Crustacea  or  insects,  and  reach  ma- 
turity only  when  the  intermediate  hosts  are  swallowed  by  the  proper  final 
host.  The  largest  species  of  Echinorhymhus  is  the  E.  gigas,  which  occurs 
in  the  intestine  of  the  pig  ;  the  intermediate  host  of  this  form  is  the  June 
bug  {Melolontha,  Lachnosterna). 

Nothing  can  as  yet  be  stated  with  any  certainty  concerning  the  relation- 
ships of  the  Acanthocephala.  They  are  usually  associated  with  the  Nema- 
todes, to  which  they  certainly  present  similarities,  but  no  intermediate 
ionns  bridging  the  gap  between  the  two  classes  are  yet  known,  and  the 
embryological  history  throws  little  light  upon  the  question 


SUBKINGDOM  METAZOA. 
TYPE  NEMA  TIIELMINTHES. 

I.  Class  NEMATODA—With  digestive  tract;  without  proboscis  furnished 
with  chitinous  hooks 
1.  Order  A'^«i^//w/rWa. -Musculature  of  body-wall  interrupted  along 
the  lateral  line  ;  no  mesentery  ;  no  peritoneal  epithelium     An- 
(fuil/ula,  Tylenchus,  Heterodera,   Trichina,  Asvaris,  Oxyuris 
Tnc/iocep/ntlus;  Dochmins,  Filaria. 


TYPE  NEMATHELMINTHE8.  183 

2.  Order  t?oyv/weea.-Musnilature  of  body-wall  not  interrupted  along 
the  lateral  line ;  wuh  mesentery  and  peritoneal  epithelium. 
Qordms,  Mermis. 

II.  Class  ACANTHOCEPHALA. -Without  digestive  tract;  with  proboscis 
armed  wuh  recurved  chitinous  hooks;  parasitic  throughout. 
EcJitnorhymhus. 

I 

LITERATURE. 

R.  Leuckart.-2?^e  Parasiten  des  Menschen.    2te  Aufl.    (In  course  of  publica- 

A.  Sohnnier.—MonogmpMe  der  Nemntoden.     Berlin,  1866. 

L.  Orloy.—Monographie  der  AvgtdUuliden.     Buda-Pesth,  1880 

J.  G  de  V.^n.-DieeAnheimuche,,,  frei  in  der  reinen  Erd'e  und  in  sussen  Wasser 

lehendenmmatod,n.     Tijscbr.  cK  Nederland.  Dierkund.  Vereen   v   1880 
T.Vejdov8ky-*<Mdu.«   uber    GordUdca.     Zeitschr.   fUr  wlssenscL.  Zoologi;, 

0.  Hamann.-3/o,u,^m;,;«e  der  Acant/wcephalen  (Echinorhynchen).    Jenaisebe 
Zeitscbr.,  xxv,  1890.  cuaistue 

'■  ^He'ft.  vu'  ^gg^"''''^'^^''"^'*  «^"^  ^'''•^  Bntu,icklung.    Bibliotheca  Zoologica. 


s 
3 

^ 


I 


A. 


184 


INVERTEBRATE  MORPUOLOQY. 


.111!  'V 


CHAPTEB  IX. 

ORDER    ECHINODERA ;    CLASS    CHiETOGNATHA  ;    CLASS 
ROTIFERA ;  ORDER  GASTROTRICHA  ;  DINOPHILUS. 

This  chapter  iucludes  a  descriptiou  of  a  number  of  forms 
^vhose  affinities  are  at  present  rather  doubtful  and  which 
show  similarities  sometimes  to  the  Nemathelmiuths  and 
sometimes  to  the  Annelida.     Instead,  however,  of  assigning 

them  to  one  or  the  other  of  these  types, 
it  has  been  thought  advisable  to  consider 
them  in  a  separate  chapter  and  each 
group  independently,  indicating  brieiiy 
their  most  probable  affinities. 

Order  Echinodera. 

The  order  Echinodera  includes  a 
number  of  small  organisms  all  marine  in 
habitat,  and  all  referable  to  a  single 
genus,  Echinoderes  (Tig.  91).  The  body 
varies  iu  length  from  somewhat  less  than 
1  mm.  to  almost  0.1  mm.  according  to  the 
species,  and  tapers  somewhat  posteriorly, 
terminating  in  one  or  two  prolongations 
or  cerci,  while  anteriorly  there  is  a  pro- 
FiG.  91.  —  Echinoderes  boscis  armed  with  strong  setae  which 
Dujardinii  (after  c,.A-  ^^   iuvaginated   within  the  anterior 

PARUDE  from  Hatschek).  •'  _  " 

portion  of  the  body,  and  serves  as  an  or- 
^aii  of  locomotion  as  well  as  for  the  prehension  of  food. 
The  outer  surface  is  covered  b}-  a  layer  of  chitin  which  is 
divided  into  distinct  metameric  rings,  the  number  of  which, 
eleven,  is  constant  for  all  known  species,  and  which  ai'e  pro- 
vided in  some  species  with  definitely-arranged  setse.  No 
•cilia  are  present.  Beneath  the  chitinous  rings  lies  the  ecto- 
<lerm,   which  shows    indications    of  metamerism  also,  being 


I 


ORDER  ECIIINODERA. 


185 


thickened  beneath  the  interval  between  two  successive  rings  • 
it  consists  of  a  granular  layer  of  protoplasm  in  which  scat^ 
tered  nuclei  occur.  Beneath  the  ectoderm  lies  a  somewhat 
incomplete  layer  of  longitudinal  muscles,  which  become  spe- 
ciahzed  anteriorly  into  separate  bundles  for  the  retraction  of 
the  proboscis;  in  each  metamere  two  dorso-ventral  muscle- 
•uudles,  one  on  each  side  of  the  middle  line,  are  also  found 
A.  relatively  spacious  body-cavity  in  which  various  organs 
he  occurs,  but  no  lining  peritoneal  epithelium  or  mesenteries 
have  been  observed. 

The  digestive  tract  begins  with  the  mouth,  which  lies  at 
the  bottom  of  the  invagiuated  proboscis  and  opens  by  the  in- 
tervention  of  a  short  tube  into  a  muscular  pharynx  into  the 
anterior  portion  of  which,  four  glands,  either  salivary  or  poi- 
souous  in  function,  pour  their  secretion.  The  pharynx  com- 
municates posteriorly  with  a  saclike  stomach,  upon  which 
follows  a  short  straight  intestine  opening  to  the  exterior  at 
the  posterior  end  of  the  body  between  the  terminal  cerci. 

Two  elongated  pear-shaped  bodies  lying  in  the  ccelom  in 
about  the  middle  region  of  the  body  have  been  described  as 
excretory  organs.  They  are  closed  at  the  free  end,  their 
cavity  is  ciliated,  and  they  open  to  the  exterior  on  the  dorsal 
surface  near  the  margin  of  the  body.  The  reproductive 
organs  are  cylindrical  sacs  which  are  provided  with  ducts 
opening  to  the  exterior  on  the  terminal  segment ;  all  the 
species  whose  reproductive  organs  have  been  studied  are 
bisexual. 

Four  cellular  masses  lying  above  the  pharynx  seem  to 
represent  the  nervous  system,  though  no  nerves  passing  from 
them  have  been  discovered  ;  nor  do  any  special  sense-organs 


The  affinities  of  these  forms  is  highly  problematical,  especially  since 
notinng  ,s  known  of  their  development.  The  metamerism  indicated  by  the 
olut.nous  ru.gs,  the  thickenings  of  the  ectoderm,  and  the  dorso-yentral 
m.Ksc  OS  suggest  an  affinity  with  the  Annelids,  while,  on  the  other  hand  in 
tl.ochitinous  covering,  and  the  occurrence  of  a  longitudinal  musculature 
only,  similarities  to  the  Nematodes  may  be  found.  The  excretory  organs 
may  perhaps  be  compared  with  the  larval  nephridia  of  the  Annelids  and 
the  existence  of  but  a  single  pair  of  them,  together  with  the  absence  of 
any  metamenc  arrangement  of  nerve-ganglia,  favors  the   idea  that   the 


]8t5 


11 


i!'l 


INVERTEBRA  TE  MORPHOLOO  Y. 


Echinodera  are  not  to  be  considered  as  being  truly  metamerlc,  indications 
of  metamerism  whicli  art  foind  being  altogether  secondary  and  without 
phylogenetic  significance.     Until,  however,  something  has  been  ascertained 

regarding  their  embryological  history  nothing  can 
be  positively  stated  as  to  their  affinities.  It  is 
worthy  of  notice,  however,  that  in  some  particulars 
they  resemble  the  Gastrotricha,  and  it  is  not  im- 
probable that  their  nearest  allies  are  to  be  found 
in  that  order,  which  on  its  part  is  related  to  the 
Rotifera  (see  p.  189) . 


\ 


/ 


■ov 


/ 


Class  Chjetognatha. 

The  Clisetognatha  constitute  a  small 
group  of  forms  separable  into  two  genera, 
Sagitta  and  Spcddla.  All  the  members 
of  the  group  are  marine,  and  are  elonga- 
ted in  form,  the  sides  of  the  body  being 
furnished  with  one  or  two  pairs  of  lateral 
expansions  or  fins,  to  which  is  added  a 
caudal  fin.  The  anterior  portion  of  the 
body  is  somewhat  enlarged  so  as  to  form 
a  head,  and  on  either  side  of  the  mouth 
are  a  number  of  strong  chitinous  bristles 
movable  by  means  of  special  muscles 
and  serving  the  purpose  of  jaws. 

The  ectoderm  consists  of  several 
layers  of  flattened  cells  giving  rise  in  the 
head  region  by  secretion  to  chitinous 
plates  which  serve  for  the  attachment 
of  the  muscles  which  move  the  jaw- 
bristles.  Both  the  lateral  and  the  caudal 
fins  are  ectodermal  expansions  consisting 
of  a  homogeneous  lamella  covered  by 
one  or  two  layers  of  ectodermal  cells. 
They  possess  no  muscle-fibres  and  are 
passive  in  locomotion,  which  is  per- 
formed by  the  contraction  of  the  longitudinal  muscles 
producing  rapid  lateral  movements  of  the  posterior  part  of  the 
body.  The  genus  Sagitta  possesses  two  lateral  fins,  while  in 
Spadella  (Fig.  92)  but  one  large  one  is  present.     Below  the 


Fig,  ^2.— Spadella  ceph- 
aloptera     (after   Hert- 

WIG). 

ce  =  cerebral  ganglion. 

i  =  intestine. 

o  =  olfactory  organ. 
oc  =  eye. 
ov  =  ovary. 

t  =  testis. 


CLASS  CH^TOONATHA. 


187 


ectoderm  lies  a  well-tletiued  basement-membrane,  and  below 
this  are  the  muscles  of  the  body-wall,  which  are,  as  a  rule, 
longitudinal  in  their  direction,  and  are  interrupted,  as  in  the 
Nematodes,  along  four  longitudinal  lines,  one  dorsal,  one  ven- 
tral,  and  two  lateral.  In  one  species  of  Spadella  there  is  ou 
the  inner  side  of  the  longitudinal  muscles  a  thin  layer  of  trans- 
verse  muscles,  but  usually  only  longitudinal  fibres  are  present, 
except  in  the  head,  when  there  are  a  number  of  special  muscle- 
bundles  for  the  movement  of  the  jaw-bristles. 

Within  the  musculature  of  the  body-wall  is  the  spacious 
coelom,  lined  throughout  by  a  delicate  layer  of  cells  constitut- 
ing the  peritoneum,  and  divided  into  three  chambers  by 
transverse  partitions,  one  of  which  lies  just  behind  the  head, 
while  the  other  is  towards  the  hind  end  of  the  body.  The 
peritoneal  epithelium  lines  the  surfaces  of  these  dissepiments, 
and  in  the  trunk  and  tail  regions  is  reflected  in  the  mid- 
dorsal  and  ventral  lines  towards  the  centre  of  the  body,  form- 
ing a  mesente.y,  surrounding  the  intestine  and  dividing  the 
ccelom  into  lateral  compartments. 

The  mouth  lies  on  the  ventral  surface  of  the  head  and 
opens  into  an  oesophagus  surrounded  by  a  single  layer  of 
muscle-fibres  having  a  dorso-ventral  direction  and  passing 
above  and  below  into  the  general  musculature  of  the  head. 
After  being  narrowed  in  passing  through  the  anterior  dissepi- 
meut  the  digestive  tube  again  expands  (Fig.  92,  i\  and  is  sup- 
ported throughout  the  trunk  region  by  the  mesentery.  In 
this  region  it  is  a  simple  straight  tube,  unprovided  with  mus- 
cle-fibres, and  terminates  in  an  anal  opening  situated  ven- 
trally  at  the  junction  of  the  trunk  and  tail  regions,  not  being 
continued  into  the  latter. 

Neither  an  excretory  nor  a  blood  vascular  system  is  pres- 
ent. The  nervous  system  lies  for  the  most  part  imbedded  in 
the  ectoderm,  and  consists  of  two  principal  ganglionic  masses, 
of  which  one,  the  cerebral  or  supraresophageal  ganglion  (ce\ 
lying  in  the  head  region,  is  situated  in  the  ectoderm  of  the 
dorsal  surface  of  the  body  and  has  a  somewhat  hexagonal 
outline,  giving  oft'  five  pairs  of  nerves,  one  pair  passing  back- 
wards  as  commissures  to  unite  \.ith  the  ventral  or  sub- 
cesophageal  ganglion,  lying  also  in  the  ectoderm  a  little  in 


188 


INVEHTEBltAl'E  MORPHOLOGY. 


front  of  the  middle  of  the  truuk  region  of  the  bodj'.  This 
ganglion  gives  off  numerous  nerves,  among  which  are  two 
principal  nerve-cords  passing  backwards  and  giving  off  along 
their  entire  length  finer  nerves  which  branch  and  tinally  lose 
themselves  in  a  tine  ectodermal  nerve-plexus  throughout 
Avhich  ganglion-cells  are  scattered.  In  addition  to  these 
ectodermal  portions  three  pairs  of  ganglia  are  found  in  the 
head  region  at  the  sides  of  the  oesophagus,  the  largest  gan- 
glion on  either  side  being  united  with  the  supraoesophageal 
ganglion  by  a  commissure.  From  the  supraoesophageal 
ganglia,  behind  the  commissures  to  the  ventral  ganglion,  a  pair 
of  nerves  pass  backwards  to  the  two  eyes  {pc),  which  lie  com- 
pletely imbedded  in  the  ectoderm  of  the  dorsal  surface  of  the 
head,  each  consisting  of  three  biconvex  lenses  imbedded  in  a 
central  pigment  mass  and  surrc^unded  on  their  outer  surfaces 
hj  a  retina  composed  of  an  outer  layer  of  cubical  cells,  a 
middle  layer  of  cylindrical  cells  with  large  nuclei,  and  an 
inner  layer  of  rod-like  structures  arranged  perpendicularly  to 
the  surface  of  the  lenses.  Behind  the  eyes  lies  a  circular  band 
of  fine  columnar  ciliated  cells  (o),  which  is  supplied  by  a  pair 
of  nerves  arising  from  the  supraoesophageal  ganglion  be- 
tween the  optic  nerves.  The  function  of  this  organ  is  doubt- 
ful, though  it  has  been  considered  olfactory.  Scattered  some- 
what regularly  over  the  body  are  numerous  round  or  oval 
eminences  consisting  of  a  number  of  central  spherical  cells 
arranged  in  two  rows  and  bearing  rod-like  bristles.  These 
are  enclosed  in  a  sheath  of  cylindrical  cells  and  below  come 
into  contact  or  are  continuous  with  terminal  nerve-branches. 
These  sensory  hillocks  are  supposed  to  be  tactile  in  function 
and  resemble  not  a  little  the  lateral  sense-organs  of  certain 
Annelids  (see  p.  210). 

The  Chsetognatha  are  without  exception  hermaphrodite. 
The  ovaries  (pv)  are  cylindrical  l)odies  lying  in  the  trunk  re- 
gion of  the  body,  one  on  each  side  of  the  digestive  tract,  and 
upon  the  outer  side  of  each  is  a  tubular  oviduct  which  ends 
blindly  anteriorly  and  opens  posteriorly  at  the  sides  of  the 
body  near  the  dissepiment  between  the  trunk  and  tail  regions 
(jf  the  body.  There  is  no  communication  apparently  between 
the  cavitv  of  the  oviduct  and  the  ovary  or  coelom,  and  the 


AMM 


CLASS  liOTlFEHA. 


189 


maimer  iu  which  the  ova  !uake  their  escape  is  yet  uuknowu. 
Both  ovaries  aud  oviducts  are  euchjsed  within  a  fokl  of  peri- 
touenm  (mesentery)  extending  from  the  sides  of  the  body. 
Tlie  testes  (/)  are  situated  behiud  the  posterior  dissepimeut, 
i.e.,  iu  the  tail  region  of  the  body,  and  consist  of  a  streak  of 
cells  on  each  side  in  the  peritoneal  covering  of  the  body-wall. 
From  these  streaks  masses  of  immature  spermatozoa  separate 
aud  float  about  iu  the  coelom  of  the  tail  segment,  uud  when 
mature  make  their  escape  through  canals,  each  of  which  com- 
municates with  the  C(»lom  by  means  of  a  fine  ciliated  openings 
and  near  its  opening  to  the  exterior  at  the  side  of  the  body  is. 
dilated  into  a  seminal  vesicle.    - 

Tlie  einbryologiciil  history  of  Sivjitta  throws  no  light  upon  tlic  jiniiiitics. 
of  these  forms.  In  structure  they  recall,  especially  in  the  arrangement  of 
their  musculature,  the  Nematodes,  aud  especially  the  Gordiacete,  but  at  the 
same  time  show  many  similarities  to  the  lower  marine  Annelids,  as  for  in- 
stance iu  the  origin  of  the  spermatozoa  from  the  wall  of  the  coelom,  and  in 
the  similarity  of  the  vasa  deferentia  to  nephridial  caiuds.  The  occurrence 
of  dissepiments  also  suggests  affinities  to  the  Annelids,  but  it  does  not 
seem  that  these  structures  indicate  a  segmentation  of  the  body,  since  the 
arrangement  of  the  nervous  system  points  to  the  conclusion  that  the  Cha;- 
tognaths  consist  of  a  single  segment.  From  the  evidence  at  present  open 
to  us  it  would  seem  that  the  Chwtoynutha  are  more  nearly  rehited  to  the 
Annelids  than  to  the  Nematodes,  but  the  relationship  must  be  regarded  as 
a  rather  remote  one,  and  it  seems  hardly  fitting  to  include  Sayitta  and  its 
allies  among  the  Annelida. 


Class  Rotifeea. 

The  Rotifers  or  "  Wheel-animalcuies "  are  microscopic 
Metazoa  which  are  widely  distributed  both  in  salt  and  fresh 
water.  They  are  unsegmeuted  forms  with  a  well-developed 
coelom,  and  are  somewhat  oval  in  form  as  a  rule,  the  an- 
terior end  of  the  body  being  surrounded  by  one  or  two 
bands  of  cilia  whose  rapid  movement  produces  the  appear- 
ance of  a  wheel,  and  has  suggested  the  popular  name  for 
the  group.  The  posterior  end  of  the  body  is  frequently  pro- 
longed into  a  usually  extensible  so-called  foot,  which  in  some 
cases  {Lacinularia)  is  furnished  Avith  adhesive  glands,  and  is- 
used  as  a  point  of  fixation,  though  the  majority  of  forms  swim 
about  freely  or  attach  themselves  only  temporarily,  the  foot 


<:!;> 


190 


INVERTEBRATE  MORPilOLOOY. 


!=i;i 


M 


having  iu  such  cases  the  form  of  a  sucker  {Philodhw),  or  ter- 

miuatiug  m  two  movable  lamellae,  Brachionus  (Fig,  93),  or  else 

being  entirely  wanting  (Asplanchna). 

The  body,  with  the  exception  of  the  anterior  portion  or 

trochal  disk,  which  bears  the  bands  of  cilia,  is  enclosed  in  a 

chitiuous  cuticle,  occasiojiallv 
comparatively  thick  and  firm, 
forming  a  case,  the  lorica,  into 
which  the  softer  parts  may  be 
withdrawn,  and  frequejitly  pre- 
senting a  delicate  sculpturing 
GJ  or  prolongations  into  spines. 
A   few  forius   (Floscularia)   se- 

-  JV 

Crete  a  gelatinous  case  within 
Qy  wi'.ich  they  live,  foreign  parti- 
cles being  sometimes  added 
to  the  secretion  ;  a  species  of 
Melicerta,  for  instance,  building 
a  case  for  itself  of  pellets  man- 
ufactured from  foreign  bodies 
and  arranged  in  obiiijue  or 
spiral  rows  and  cemented  to- 
gether i)y  the  gelatinous  secre- 
tion. 

,p,.,   no     D     ;  •  .    .  '^'^^^  frochnl  dink  wiiich  oc- 

*xo.  vA.—BniciiioHus  nrceolaria  (after         •        ,i  ,      .  ,     „ 

cupies  the  anterior  end  of  the 

body  is  but  rarely  circular  in 

outline ;     more    usually    it    is 


ECKSTKINI, 

Br  —  ueive-ganj^lioii. 

cv  =  coMimctile  vesicle. 

(-H  =  (linostivegliviid. 

M  =  miiscie. 
Ma  =  miistax. 

N  =  nepliiidicl  caual. 

0  =  oye. 
Oc  =  ocellus. 
(h  =  oviuy. 
8p  =  calcnr. 


lobed  at  its  margins  and  mav 


even  be  se))arated  into  two 
parts.  The  margin  o.i  the  disk 
is  surrounded  by  one  or  two 
bands  of  i'ilia  which  follow  the 
lobations,  when  two  bands  are 
present  one  being  entirely 
prnooral  and  the  other  postoral  in  its  position,  so  that  the 
mouth  lies  between  the  two  on  the  ventral  side  of  the  disk. 
Various  differences  of  arrangement  oi  the  bands  are  found 
iu  dillerent  species,  one  of  them,  the    i)raH)ral,   being  som*- 


CLASS  liOTIFEHA. 


191 


times  discontinuous,  as  in  BracMomis,  or  retluced  to  a  few 
isolated  patches,  as  in  Asplanchna. 

It  is  a  question  whether  the  forms  with  a  double  band  of  cilia  or  those 
ill  wliich  it  is  single  represent  the  more  primitive  arrangement.  It  may  be 
supposed  that  originally  there  was  but  a  single  band  which  later  became 
double,  but  it  seems  more  probable  that  the  double  condition  is  tlie  more 
primitive,  from  the  fact  of  its  frequent  occurrence  and  also  P'nce,  when 
a  single  band  is  present,  it  seems  to  represent  in  some  cases  the  pra>- 
oral  baud  and  in  others  {Floscuhiria)  the  postoral  one.  Such  a  condition 
of  affairs  can  be  most  plausi^'y  explained  on  the  assumption  that  originally 
two  bands  were  present,  and  that  in  some  forms  the  prttoral  one  gradually 
gained  i)re-eminence  in  its  development,  the  postoral  one  disappearing  pari 
passu,  while  in  the  Flosculariidoe  the  reverse  was  the  case. 

Beneath  the  cuticle  lies  the  ectoderm,  consisting  of  a  layer 
of  cells  whose  outlines  cannot  be  distinguished,  and  within 
this  comes  the  musculature  of  the  body,  which  does  not,  how- 
ever, form  a  more  or  less  continuous  layer  beneath  the  skin, 
but  consists  of  aggregations  of  muscle-fibres  into  bundles 
which  traverse  the  body-cavity  in  various  directions,  some 
running  longitudinally  and  forming  retractors  of  the  foot  and 
of  the  trochal  disk,  while  others  have  a  circular  direction.  The 
coelom,  in  which  the  muscle-biiudles  and  the  various  organs  lie, 
is  not  lined  by  a  special  peritoneal  layer  of  cells,  but  may  be 
traversed  by  a  greater  or  less  number  of  delicate  fibrils 
arising  from  amceboid  cells  and  representing  uudiflerentiated 
mesoderm. 

The  mouth  lies  near  the  ventral  border  of  the  trochal  disk, 
the  ciliated  bands  serving  to  produce  currents  which  con- 
verge toward  the  month-opening,  and  so  carry  to  it  food-parti- 
cles, which  are  then  carried  through  the  ciliated  «i!Sophagus 
to  the  i-harynx,  whose  walls  contain  a  somewhat  compliciated 
comminuting  apparatus,  the  ma-sfax  (Fig.  U3,  ma),  consisting 
of  two  calcareous  bodies,  the  laaUei,  of  varying  shajx',  and 
sometimes  also  of  a  median  body,  the  iitrm.  By  tl  i  action  of 
muscles  attachec]  to  the  mallei,  these  parts  of  the  appiiratus 
can  be  brought  into  contact  with  each  other,  and  with  the 
iucub  when  this  is  ])r('seut,  the  food-particles  btung  thus 
comminuted.  From  the  pharynx  the  food  passes  through  a 
shorter  or  longer  tube  lined  with  chitin,  which  is  to  Ik» 
regarded  as  a  continuation  of   the  pharynx,  to  the  stomach, 


192 


iiV  VERTEBRA  TE  MORPHOLOO  Y, 


3 


usuiilly  a  globular  cavity,  whose  wall  i«  formed  by  a  layer  of 
ciliated  cells  coutainiug  fat-globules  aud  various  other  par- 
ticles, probably  absorbed  food-particles,  these  cells  being 
covered  externally  by  a  layer  of  couuective  tissue.  Into  the 
stomach  there  opens  from  either  side  the  duct  of  a  gland  (gl), 
whose  secretion  is  probably  digestive  iu  function  and  which 
may  be  termed  a  digestive  gland  from  its  resemblance  to 
similarly  located  glands  in  other  invertebrates.  The  stomach 
opens  below  into  the  shorter  o)-  longer  intestine,  whose  walls 
are  lined  by  ciliated  cells  ;  aud  this  in  turn  communicates  with 
the  terminal  cloaca,  which  receives  iu  some  cases  the  termi- 
nations of  the  excretory  tubules  and  m..y  be  contractile. 
The  cloaca  opens  to  the  exterior,  usually  on  the  dorsal  sur- 
face, near  the  base  of  the  foot,  though  iu  some  forms  which 
live  within  a  case  the  intestine  bends  forward  upou  itself,  so 
that  the  cloacal  opening  lies  further  forward. 

The  nervous  system  consists  of  a  relatively  large  ganglionic 
mass  {lir)  lying  on  the  dorsal  side  of  the  ajsophagus,  from 
which  nerves  pass  anteriorly  to  the  trochal  disk,  and  posteriorly 
to  sui)ply  a  dorsal  sensory  papilla,  the  calair  (Sp).     In  addi- 
tiou  to  this,  two  pairs  of  posterior  nerves  have  beeu  described, 
one  of  which  i)asses  to  a  sense-organ  situated  on  each  side  of 
the  body  in  its  posterior  third,  while  the  other  pair  runs  back- 
wards on  each  side  of  the  middle  line  to  near  the  posterior 
end  of  the  body,  giving  off  branches  to  the  musculature  as 
it  goes.     Among  the  sense-organs  eyes  (O)  are  very  geuerally 
present,  varying  in  number  from  one  to  several,  and  situated  in 
the  region  of  the  supraiesophageal  ganglion,  with  which  thev 
are   connected.     Tiiey  consist  of    patches  of  red,  brown,  or 
black  pigment  with  which  sensory  or  retijial  cells  are  asso- 
ciated, ami  which  are  in  some   cases  covered  by  a  refracting 
lens  formed  as  a  special  cuticular  thickening.     Other  sense 
organs  to   which    a    tactile   function  has  been  ascribed  con 
sist  in  their  simplest  form   of  one  or  several  cells  beariii  ■ 
stiff  cilia.     A  jjaii  of  such  organs  is  usually  present,  one  on 
each    side   immediately   above    the    ganglion    of   the    iateiul 
nerves,  and  anteriorly  in  the  mid-dorsal  line  just  behind  Uw. 
trochal  disk  a  third  occurs,  the  cnlcar  (Sp),  which  freoueutlv 
is  situated  upon  the  extremity  of  a  tubular  extensible  ])iocess 


CLASS  ROTIFEHA. 


193: 


of  tlie  body-wall,  supplied  with  muscles  for  its  retraction,  aud 
to  which  uerve-fibres  pass  from  the  supraoesophageal  gauj^lion. 
Ill  a  few  forms,  such  as  Melicerta,  the  calcar  is  double. 

No  blood  vascular  system  exists,  b'lt  a  well-developed 
excretory  apparatus  {N),  resembling  that  of  ilie  Turbellaria, 
is  present.  It  consists  of  two  longitudinal  tubes,  one  on  each 
side  of  the  body,  from  which  arise  a  varying  number  of  tiner 
lateral  branches,  each  of  which  terminates  in  a  funnel  closed 
by  a  iianie-cell,  as  in  the  Turbellaria.  Anteriorly  the  two 
Uibes  may  be  united  by  a  transverse  connecting  tube,  and 
posteriorly  they  may  unite  together  to  form  a  contractile 
bladder  which  opens  into  the  cloaca,  or  in  some  cases  may 
Dpen  directly  to  the  exterior. 

The  female  reproductive  apparatus  consists  of  a  relatively 
largo  ovary  {Ov)  which  in  some  cases  at  least  consists  of  a 
vitellarium  portion  and  an  ovary  proper,  the  whole  being 
surrounded  by  a  thin  membrane  a  backward  prolongation  of 
which  forms  an  oviduct  opening  into  the  cloaca. 

The  preceding  descrii)tion  of  the  structure  of  a  llotifer  is 
that  of  such  a  form  as  is  most  frequently  met  with.  It  was 
for  a  long  time  believed  that  these  were  hermaphrodite,  but 
no  trace  of  a  testis  could  be  found.  It  was  later  found,  how- 
ever, that  they  were  all  females,  and  the  males  of  several 
species  have  been  discovered,  differing  decidedly  in  size  and 
structure  from  the  females,  and  besides  being  usually  rather 
rare  in  their  occurrence.  They  are  considei  ny  smaller  than 
the  female,  and  possess  like  it  eyes,  nerve-ganglion,  muscles, 
and  excretory  system  ;  but  the  ciliated  band  of  the  trochal 
disk  is  single,  and  the  digestive  tract,  with  the  exce])tiou  of  the 
cloaca,  is  reduced  to  a  solid  band  of  tissue.  The  single  testis 
occupies  the  greater  portion  <>f  the  body-cavity,  and  the  short 
vas  deferens  opens  into  the  cloaca,  passing  through  an  evertible 
iutromittent  organ.  This  marked  difference  of  ft)rm  of  the 
male  and  female  indiv'duals  of  the  same  si)ecies  constitutes 
a  phenomenon  known  as  sexual  (iliuorphism.  An  expbunitiou 
of  the  usual  numerical  preponderance  of  the  femah^s  over  tiie 
males  is  to  be  found  in  tin*  fact  that  under  favorable  condi- 
tions the  females  produce  '>vh  capable  of  developing  }>arthe. 
uogenetically,  and  giving  rise  in  all  cases  to  females.    A  series 


194 


IN  VBHTEBliA  TE  MOliPIIOLOG  Y. 


inn 


of  geiieratious  reproducing  by  these  so-called  "summer  ova  " 
may  thus  succeed  each  other  without  the  interveution  of  a 
male.  Under  certaiu  coiulitious,  however,  certain  females  pro- 
duce "  summer  ova  "  of  a  smaller  si;«e  than  usual,  which,  devel- 
oping partheuogeuetically,  give  rise  to  the  males.  In  addition 
to  these  two  forms  of  "  summer  ova,"  some  species  produce  a 
third  kind  of  egg,  the  so-called  "  winter  ovum,"  which  differs 
from  the  summer  ova  in  containing  more  yolk  and  in  being 
enclosed  within  a  stout  resistant  shell.  It  seems  probable 
that  these  ova  develop  only  after  fertilization. 

Thoro.-uv  two  liotifers  wliicli  do.servo  a  spocialdescriiXion  on  account  of 
thoir  having  served  as  a  basis  for  pliyio^c^nctic  spocnlation.     One  of  tiiose, 

TrovhosplHrm  ( Fig.  94),  is  spherical 
in  sliap«'  ;  a  l)aiid  of  cilia  runs  rouisd 
the  equator  of  the  sphere,  not  encirc- 
ling it  completely,  however,  but  leav- 
ing an  unciliated  region  on  the  dorsal 
In     surface.     Anteriorly  this  baiul  passes 
|M    above  the  mouth-opening,   which   is 
^^^**  bounded  below  by  a  very  small  post - 
oral  band  and  opens  into  a  pharynx 
provided   with   a  inastax  (Mi),  from 
whicii   the    stomach,   with    digestive 
glands,  passes  towards   the  centre  of 
the   body   and    liiere  bends  at   rigiit 
Fm.   QL—Trochosph,rra   (tquatovialis  angles  to  open  liirough  tlu-  intestine 

' i'l'o  ii  cloaca  (C/)  whicii  receives  the 

cxcrelorytubuIes{/i»  and  the  oviducts 
nnd  opens  to  the  exterior  at  tiie  lower 
pole  of  the  sphere  {A).  The  brain  (.V) 
lies  above  the  pharynx  and  sends 
nerves  to  the  two  eyes  siliialed,  one 
on  each  side,  below  the  e(iuatnri,il 
band  of  cilia,  and  also  to  a  small 
sensory  papilla  (.SV)),  proi»abIy  the 
calcar.  lying  on    the  dorsal   surface. 

this  nerve  (//)  encireling  the  anterior 
half  of  the  sphere,  and  running  in  a  plane  at  right  angles  to  that  in  which 
the  eili;ii(>d  l»and  lies. 

The  other  form  belongs  to  the  genus  mrarffiiv  and  differs  from  other 
Rotifers  principally  in  the  oeciirrenee  of  six  hollow  processes  of  the  ImmIv 
arising  from  the  ventral  surface  and  arranged  in  pairs  diminishing  in  si/e 
trom  before  Iwickwards.     Kaeh  is  terminated  by  a  bunch  of  .stiff  i)ri.stles  „>■ 
seta',  and  all  are  supplied  with  mu-scles  whereby  they  can  be  rapidly  swept 


(iiftor  Sk.mi'kh). 

A  =  anus 

Cl  =  eloHCM. 
E.r  -  excretory  tube. 

M  -  iiiouih. 
Ma  =  iiitistax. 
mil  -  muscle. 

N  =  nervegaiigllou. 

n  =  nerve. 

0  =  ovary. 
8o  -  seiiseorgaii. 


OIWER  GASTROTlilCUA. 


195 


backwards  in  the  manner  of  a  paddle  and  so  serve  as  locomotor  organs,  i)ro- 
ducing  a  quick  jerky  movement  quite  different  from  the  steady  progression 
ojuised  by  the  cilia  of  the  trochal  disk.  In  another  nearly  related  form, 
I'edalhn,  six  processes  are  also  present,  but  are  ari-anged  somewhat  differ- 
^■ntly  from  those  of  Hexarthnt,  the  largest  one  arising  from  the  ventral 
and  another  from  the  dorsal  surface,  while  the  other  four  are  lateral  iu 
position,  two  occurring  on  each  side. 

The  Affinilies  of  the.  Jiot/feru.—Saveval  views  have  been  advanced  as 
to  the  affinities  of  the  Rotifers,  especially  as  regards  their  relationships  to 
higlier  forms  ;  these  opinions  will  not,  however,  be  fully  considered  here, 
l)ut  merely  indicated,  attention  being  directed  first  to  the  relationships  in 
which  the  Kotifcrs  stand  »  >  organisms  lower  in  the  scale.  In  this  connec- 
tion the  excretory  .system  becomes  of  no  little  importance  on  account  of  its 
resemblance  to  that  of  the  Turbellaria,  a  resemblance  which  is  further 
emphasized  by  the  nervous  system,— consisting  of  the  simple  brain,  from 
wliieh  posteriorly-directed  nerve-cords  arise,— by  the  combined  ovary  and 
vitellarium,  and  by  the  ab.sence  of  a  blood  vascular  system.  Here,  how- 
ever, the  resemblance  ceases,  and  the  presence  of  an  anal  opening  to  the 
digestive  tube  marks  the  Rotifers  as  standing  on  a  higher  level  than  the 
Turbellaria.  It  .seems  probabh;,  however,  that  the  similarities  do  indicate 
the  ancestry,  and  that  the  Rotifera  have  been  derived  from  the  Turbellarian 
type. 

Another  possibility  which  has  been  suggested  is  to  the  effect  that  they 
are  derived  from  the  form  represented  by  the  Trofihophore  larva  of  the 
Annelida  (see  p.  2i;{).  The  principal  argument  for  this  view  is  found  in  the 
arrangement  of  the  trochal  cilia,  which,  in  the  occurrence  in  many  cases  of 
both  ])rieoral  and  postoral  bands,  certainly  resembles  not  a  little  that  of 
tlie  Troehophore  larva.  It  must  be  remembered,  however,  that  the  similar- 
ity ii:  the  arrangement  of  the  cilia  is  not  quite  perfect,  and  that  it  may  be 
without  phylogenetic  significance,  having  been  accpiired  indejtendently  in 
the  Rotifers  and  in  (he  Troehophore  larva  ;  and  furthermore  it  is  noticeable 
that  in  one  important  eiiaracter  at  least  a  marked  difference  is  found,  the 
nervous  ganglion  lying  in  the  Rotifers  beliind  instead  of  before  the  pru'oral 
band  of  cilia.  The  most  that  can  be  said  at  present  is  that  the  Rotifers 
show  closer  struetural  aflinities  to  the  Turbellaria  than  to  any  oth(!r  group, 
and  that  it  is  jirobable  that  they  represent  the  culmination  of  aline  i>\' 
<levelopment  originating  in  that  group,  and  furthermore  that  it  is  po.ssible 
that  they  represent  the  ancestral  anuelid  form  indicated  by  the  Troeho- 
iihore  larva. 


Order  I.  strotricha. 

Tlie  Gastrotric'lia  are  luiiiute  foriui-',,  few  exceeding  0.2  luin. 
ill  lengtli,  which  occur  in  fresh  water  and  have  aa  eh)ngated 
form  flattened  somewhat  on    the   ventral   surface,   taperinjj; 


106 


I 


Ji\  VERTEBliATK  MOIIPIIOLOGY. 


!  !1 


■       I 


^>cpht 


posteriorly  to  end  usually   in  oue  or  two  cercnl  jirocesses, 
uud  anteriorly   show  n  dilutatioii  succeeded   b-  u    more  or 
less   well-niiirked  narrow  region,   the    two   giving   rise    to   a 
head  and  neck.     The  body  is  covered  upon  the  outside  by  a 
ciiticle,  which  may  be  smooth  as  in  the  genus  Jchtluidinin,  ov 
take  the  for-n  of  overlapping  scales  as  in  Cha'tonoim\Yh^.  95), 
sometimes  bearing  spine-like  prolongations.     Along  the  ven- 
tral surface  two  bands  of  cilia  run  from 
the  posterior  part  of  the  head  region 
almost   to  the  hind  end  of  the  bodv, 
and    in  addition    to   these   patches  i)f 
cilia  are  found  upon  the  ventral  surface 
and  on  the  sides  of  the   head,  some  of 
which  are  undoubtedly  sensory  in  func- 
tion.    Beneath  the  cuticular  covering 
lies  the  ectoderm  in  the  form  of  a  laver 
of  i)rotoplaHm  in  which  no  cell  outlines 
can  be  perceived,  but  which  contains 
numerous    scattered   nuclei.      A   pair 
of   longitudinal    muscle-bands   lie   be- 
neath the  ectoderm  on  the  dorsal  sur- 
face,   and    other   bands    traverse    the 
coelom  in  anantero-posterior  direction. 
Transverse  and  circular  muscles   are, 
however,  absent.     A  distinct  cadom  is 
present,  the  greater  portion  of  which 
is  occupied,  however,  by  the  internal 
organs  ;   it  is   not  lined  with    a   i)eri- 
toneal  epithelium,  nor  are   any  mesen- 
teries j)resent. 

The  mouth  is  situated  at  the  an- 
terior extremity  of  the  body  and  opens 
into  a  muscular  (esophagus  {w),  which 
opens  in  turn  into  the  cylindrical 
stomach  (/").  To  this  succeeds  a  short  intestine  opening  to 
the  exterior  at  the  posterior  extremity  of  the  bodv. 

No  blood  vascular  system  is  present,  but  the  excretory  sys- 
tem consists  of  a  single  i)air  of  much-convoluted  tubes  (nephv) 
-which  terminute  at  one  ep.-l  i..    «   closed  ciliated   "funnel" 


Fio.  9r).  —  C/i,ftoiiotus  maxi- 
III NH  lafier  Zklinka). 

Cff   =    IHTVt'  ifJl'lglioil. 

Ur  -  gliiiuis. 

i  =  iutt'siiiie. 
vi  =  liiiigiiiKiinal 
inusclo.s. 
iie/)/ir  =  nepluidiii. 
w  =  u^isoplmgiis. 
or  =  ovary. 


OlWEIi  OASTItOTIilCflA. 


197 


while  ut  the  other  the_^  open  on  the  ventral  side  of  the  both' 
to  the  exterior.  The  reproductive  system  (ov)  ccnisists  of  two 
groups  of  geriu-cells  lying  in  tlie  posterior  part  of  the  body, 
one  on  each  side  of  the  digcistive  tract,  but  no  oviduct  has  been 
(IcHnitely  made  out  to  exist.  With  regard  to  the  testes  some 
uncertainty  exists,  an  oval  body  lying  in  the  same  region  of 
the  body  as  the  ovaries,  but  beneath  the  intestine,  having  been 
(Itiscribed  as  such  an  organ,  though  the  idtMititication  is  o])en 
to  (piestion.  If,  however,  the  body  in  question  be  the  testes, 
the  animals  are  hermaphrodite.  As  in  the  case  of  the  female 
organ  no  ducts  have  been  observed  leading  from  the  testes, 
and  nothing  is  known  as  to  the  method  by  which  the  sexual 
products  are  extruded. 

The  nervous  system  {n)  consists  of  a  large  ganglionic  mass 
which  lies  above  the  (esophagus  in  the  head  region,  and  from 
the  posterior  border  of  which  two  processes,  one  on  each  side 
of  the  middle  line,  are  directed  posteriorly  and  dorsally, 
p(U-haps  representing  the  origin  of  a  pair  of  nerves,  Avhile  the 
l)ostero-external  angles  of  the  ganglionic  mass  are  continued 
l»ackwards  to  near  the  posterior  extremity  of  the  body  to 
form  the  hiteral  nerves.  Certain  of  the  elongated  cilia  found 
on  the  head  no  doubt  function  as  sense-organs,  coming  into 
intimate  connection  at  their  bases  with  the  cells  of  the  supra- 
(esophageal  ganglion ;  in  additicm  to  these  sense-organs  eyes 
have  also  been  described  as  occurring  in  some  species,  either 
in  the  form  of  sim})le  patches  of  pigment  lying  in  the  integu- 
ment above  the  brain,  or  else  of  such  i)atches  provided  with 
lens-like  structures. 

TIk!  jiffinitics  of  tlio  Gastrotrkha  seem  almost  certainly  to  be  with  tiie 
Uotifora,  iiiiuiy  of  lii«  stnictiiral  f.'atiu-cs  being  oxfoodiiigly  similar  in  the 
two  groups.  The  principal  ditrereiices  arc  to  be  found  in  the  arraiigeuHitit 
of  the  cilia  and  in  th.^  structure  of  the  nephridia.  With  regard ''to  the 
former  it  seems  not  improbable  that  in  the  arrangement  seen  in  the  Gastvo- 
trirhi  a  relic  of  a  more  primitive  uniform  ciliation  is  presented,  and  that 
in  this  particular  as  well  as  in  the  greater  simplicity  of  the  digestive  tract, 
■■•lid  in  the  general  form  of  the  Ixxly  and  life-habits,  the  Omtrotrhha 
api)roach  more  n.'arly  an  ancestral  Turbellarian  form  than  do  tlui  liolifera. 
Tlie  nephridia  depart  much  more  widelv,  however,  from  the  Turbellarian 
condition  tlmn  do  those  of  the  liolifera -a  fact  whic^h  argues  against  fh( 
more  primitive  character  of  the  Gastrotrich 


of  ducts  for  llio  teproductiv 


n.  as  does  likewise  the  ai.'scn* 
e  organs.     Whether,  therefore,  the  Gaslrotrk'ha 


108 


INVERTEBRATE  MORPIIOLOOT. 


i 


!  m 


'■ 


\ 


are  to  bo  considenui  as  representing  the  ancestral  form  from  which  both 
they  and  the  Kotifera  liave  descended  more  nearly  than  the  latter  group, 
or  wliether  they  are  moditieations  of  the  Kotifer  type  of  structure  and  havo 
had  tor  their  ancestors  forms  whicii  were  Kotifer-like  in  structure,  it  is 
difficult  to  say ;  thougli  the  balance  of  evidence  seems  to  tij)  in  favor  of 
the  former  view. 

Attention  should  be  called,  however,  to  a  possible  affiliation  of  the  Oas- 
trotrutlia  with  the  Echinodera.  If,  as  has  been  suggested  (p.  186),  the  seg- 
mentation of  the  latter  has  no  phylogenetic  signiticance,  it  is  not  difficult 
to  trace  similarities  of  structure  in  the  two  groui)s,  the  principal  differ- 
ences being  connected  vvitli  external  parts.  It  is  by  no  means  improbable 
tliat  the  Gastrotriclia,  Kotifera,  and  Echinodera  form  a  series,  eacli  of  the 
groups  being  of  equivalent  rank,  and  related  to  each  other  somewhat  as 
are  the  Turbellaria,  Trenuitoda,  and  Cestoda. 


Genus  Dinophilus. 

The  geuus  Dinophilus  includes  some  small  marine  organ- 
isms all  of  which  are  •  ferable  to  a  small  number  of  species. 
The  body  (Fig.  96)  is  cylindrical  and  consists  of  a  head  segment 
followed  by  from  5-7  trunk  segments  (tlie 
number  varying  according  to  the  species), 
each  of  which  bears  a  ring  of  cilia,  inter- 
rupted ventrally  by  a  uniform  ciliation  which 
covers  the  entire  ventral  surface.  The 
head  is  likewise  provided  with  a  ring  of 
cilia  which  is  usually  double,  one  of  the 
constituent  bands  passing  in  front  of  the 
mouth  and  the  other  behind  it,  the  area  in- 
tervening between  these  two  bands  being, 
in  one  species  at  least,  occupied  by  smaller 
cilia.  The  musculature  of  the  body-wall 
is  but  weakly  developed,  though  both  uu 
external  layer  of  circular  fibres  and  an  in- 
ternal one  of  longitudinal  fibres  may  be 
found,  both  layers  being  absent  iu  o\w 
species  in  the  dorsal  region.  The  coeloin 
is  traversed  by  a  network  of  branching  cells, 
there  being  no  special  peritoneal  layer,  and 
no  musculature  in  the  walls  of  the  intestine. 
The  mouth  is  situated  on  the  ventral  surface  at  the  juno- 
1  of  the  head  and  first  trunk   segments,  and  leads  into  a 


Fig.  QQ.— Dinophilus 

fU/rociliatus     (after 

."^UVKRt. 

«('  =  nepliridium. 

or  =  oviuy. 

sg  =  salivary  gland. 


OENUS  DJNOPIIlLVa. 


109 


wide  ciliated  oesophagus,  beneath  which  lies  a  mu^.ular  pro- 
boscis contained  in  a  special  sheath  and  protrusible  through 
the  mouth-opening.  Behind  the  oesophagus  is  a proventricvL, 
a  sma  1  thick-walled  ciliated  cavity,  into  which,  at  its  junction 
with  the  CBsophagus,  a  pair  of  salivary  glands  {sg)  pour  their 
secretion.  Behind,  the  proventriculus  communicates  with  a 
cylindrical  stomach,  upon  which  follows  the  short  straight  in- 
testine, terminating  in  the  anus  at  the  posterior  end  of  the 
body. 

There  is  no  blood  vascular  system.    An  excretory  system 
is  present,  consisting  in  D.  gyrociUatus  and  D.  tceniatus  of  five 
pairs  of  nephridia  (ne)  which  open  externally  on  the  sides  of 
the  body  and  terminate  in  the  coelom-spaces  in  a  funnel  con- 
taining a  flame-like  bunch  of  cilia.     Whether  a  direct  commu- 
nication between  the  lumen  of  the  nephridial  tubes  and  the 
CO.  om  exists  in  all  cases  has  not  been  definitely  ascertained, 
but  a  similarity  of  structure   to  the  Platyhelminth  tvpe  of 
iiephndium  is  shown  by  the  flame-like  bunch  of  cilia  ^nd  by 
each  nephndium  being  composed  of  a  series  of  perforated  cells 
Jhe  reproductive  organs  are  separated  in  diflferent  individu- 
a  s ;  and  in  one  species,  D.  gyrodUatm,  a  marked  sexual  dimor- 
plnsm  similar  to  that  occurring  in  the  Rotifera  exists,  the 
luale  being  much  smaller  than  the  female  and  possessing  only- 
he  ciliated  ring  of  the  head  and  the  ventral  ciliation ;  and 
furthermore   the   digestive    tract  and   the    principal    sense- 
organs  are  entirely  wanting.     The  reproductive  elements  (ov) 
are  shed  into  the  coelom-spaces  and  find  their  way  to  the  ex- 
tenor  in  some  species  at  least  by  means  of  the  most  posterior 
pair  o   nephridia,  which  in  the  male  of  D.  ta^niatm  are  trans- 
tormed  into  seminal  vesicles  and  are  connected  with  an  intro- 
■nittent  organ  situated  in  the  posterior  segment 

The  nervous  system  consists  of  a  brain  or  supraoesophageal 
.aughonic  mass  which  occupies  the  greater  portion  V^the 

dsTr  iT  l'-'^'^ .^'^'^'^  *-  nerve-cords  pass  back- 
AN  aids  m  the  lateral  region  of  the  body,  and  in  D  tmiiatm 
possess  ganglionic  enlargements  equal  in^'number  to  t  .e: 

t  nephridia  and  the  trunk  segments  and  are  connected  by 
tiausverse  commissures.  In  otb^r  «r.n.ieo  i.^^.^^-  .,  ^ 
-uctures  have  .ot  been  o^.^,.  ^  E^lt'oetTLbeS 


200 


INVERTEBRATE  MORPUOLOOY^ 


iu  the  substance  of  the  supraoesophageal  ganglion,  and  tactile 
hairs  occur  at  various  regions  of  the  body. 

Affinities  of  Dinophilus. — The  descriptions  given  of  the  various  known 
species  of  Dinophilus  indicate  a  considerable  variation  in  the  structure  of 
certain  parts,  more  especially  of  the  nervous  system,  which  in  D.  tivniatus 
partakes  of  the  metamerism  shown  by  the  uepliridia  and  the  bands  of  cilia, 
while  in  other  forms  it  is  apparently  non-metameric.  Tliis  would  indicate 
either  that  the  metamerism  has  been  acquired  within  the  limits  of  tliu 
genus,  or  else  that  those  forms  lacking  it  are  degraded  in  this  respect  and 
have  descended  from  metameric  ancestors.  There  is  little  justification  to 
be  found,  however,  for  the  calling  in  of  degradation  to  explain  obscure  re- 
lationships unless  there  is  sufficient  collateral  evidence  to  support  such  an 
appeal ;  in  the  present  case  this  seems  to  be  absent,  and  the  marked  simi- 
larity of  the  non-metameric  nervous  system  to  that  of  the  Turbellaria  sug- 
gests an  origin  from  these  forms  and  favors  the  first  hypothesis  as  to  the 
origin  of  the  metamerism.  The  nephridia  also  and  the  character  of  the 
coelom  strengthen  the  probability  of  a  Turbellarian  ancestry. 

A  close  relationship  to  the  Rotifera  has  also  been  suggested  and  is  not 
debarred  by  the  supposition  of  a  descent  from  Turbellarian  forms  ;  but  it 
seems  doubtful  if  such  a  relationship  can  be  other  than  a  very  distant  one. 
Tlie  position  of  the  supraoesophageal  ganglion  relatively  to  the  cephalic 
cilia  ov  prototroch,  and  the  paired  arrangement  of  the  nephridio  as  well  as 
the  occurrence  of  circular  fibres  in  the  subepidermal  musculature,  stand 
in  opposition  to  the  view,  and  the  most  that  can  be  said  is  that  both 
Dinophilus  and  the  Rotifera  are  to  be  referred  back  to  closely-similar 
ancestors. 

The  affinities  of  Dinophilus  and  the  Rotifers  to  the  Annelida  will  bo 
discussed  in  connection  with  the  latter  group  (p.  217). 

SUBKINGDOM  METAZOA. 

Order  Eehinoder a.— Body  cyUndrical,  with  11  rings  ;  no  cilia  ;  with  pro- 
boscis ;  minute  forms  ;  marine.     Echiiioderes. 

Class  Oh^tognatha. — Marine;  body  divided  into  three  segments;  witli 
lateral  and  tail  fins  ;  mouth  with  chitinous  jaws  composed  of 
series  of  strong  bristles.     Sagitla,  Spadella. 

Class  Rotifera. — Anterior  end  provided  with  a  retractile  crown  of  cilia  ; 
minute  forms  both  aquatic  and  marine.  Floscularia,  Melicerta, 
Lacimilaria,  Philodina,  Brachionus,  Asplanchna,  Trocho- 
sphcei'a,  Pedalion,  Hexarthra. 

Order  Gastrotricha.—Mmnte  forms  both  marine  and  aquatic ;  ventral  sur- 
face of  body  ciliated ;  no  anterior  crown  of  cilia.  Ichthydiuin, 
Chittonotus. 

Gqhws,  Dinophilus.— ^maW  marine  forms;  body  with  5-7  segments,  each 
with  a  ring  of  cilia. 


GENUS  DlJSOPHlLUa. 


201 


LITERATURE. 

ECHINODERA. 

W.Keinhard.    Kinorhyncha  (EcMuoderes),   ihr  anatomischer  Ban   und  ihre 
btdlung  im  System.    Zeitschr.  fUr  wissensch.  Zoologie,  XLV,  1687. 

CHiETOGNATHA. 

O.Hertwig.  Die  Chmtognathen.    Eine  Monographie.    JeBaische  Zeitschr. .  xiv. 

ROTIFERA. 

C.  T.  Hud.on  and  P.  H.  Gosse.     The  PMifera  or  Wheel-animalcuUs.    London, 
^  ^^T'  -.Sf '^^'  '''''  ■^«^«^5'««cA^A«e  der  Rotatorien.    Jenaisclie  Zeitschr. 

XIX,  looO.  ' 

C.Zelinka.    Studien  ilher  mderthiere.    Zeitschr.  fttr  wissensch.  Zoologie  XLiv 
1886  ;  XLVir,  1888 ;  liii,  1891.  ^ 

GA8TR0TRICHA. 

C.  Zelinka.    Die  OastrotricJien.    Zeitschr.  f ttr  wissensch.  Zoologie,  xlix,  1889. 

DINOPHILUS. 

1.  Korachelt.     UeberBau  und  Entwicklung  des  Dinophilvs  apatris.    Zeitschr 
tur  wissensch.  Zoologie,  xxxvii,  1883. 

^xx;n;788r°'    ^*''^'^^"^"*^^«*-  '  Q"^"«^Jy  J«^r'^-  of  Microscop.  Science, 


iii-iiiiMiiif 


202 


INVERTEBRATE  MORPHOLOGY. 


CHAPTER  X. 


TYPE    ANNELIDA 


The  type   Annelida   includes    a   series   of  forms  amoiif:^ 

which  metamerism  reaches  a  high  grade  of  development.     In 

what  may  be  considered  a  typical  Annelid 

(Fig.  97)  a  number  of  segments  or  meta- 

meres    succeed    one    another    from    the 

head  to  the  tail,  each  one  resembling  its 

predecessor  and  its  successor  in  all  its 

parts  ;  the  nephridia,  reproductive  organs, 

nerve-ganglia  {n),  and  appendages,  when 

present,  are  repeated  in  each  successive 

segment,  and  each  metamere  is  marked 

off  from  its  fellows,  externally  by  a  groove 

surrounding  the  body  and  internally  by 

a    partition    or    dissepiment    extending 

transversely  across  the  ctelom  from  the 

body-wall   to   the  digestive    tube.     This 

latter  structure  and  the   blood  vascular 

tubes   cannot   well    from    the  nature    of 

things  be  divided  metamerically,  but  are 

continuous  from  one  end  of  the  body  to 

the  other,  showing,  however,  in  the  meta- 

K^a  meric  pouches   and  intenne tumeric  con- 

■n.       nry     rkr.^«  ,,  ^™  strlctlous  of  tlie  digest'* ve  f  .ict    and  in 
Fig.   97. — Diagram  of  .  . 

General  Plan  of  an  the  metamerically  arranged  lateral  vessels 

of  the  blood  vascular  system  which  encir- 
cle the  digestive  tube,  indications  of  the  di- 
vision which  has  affected  the  other  organs. 
Two  segments,  however,  the  heiul 
(pr)  and  the  tail,  usually  present  differ- 
ences from  the  rest  in  their  structure ; 
the   head  or   anterior   metamere    boars   senso-orgaus  when 


ANiNELID. 

a  =  :uius. 

ce  =  cerebral  ganglion. 
m  ™  uuiu  It 

n  —  "'n   ••  '  nerva  co»"d. 
pr  =  j>ro9'<  laiiiui. 


TYPE  ANNELIDA. 


208 


tliese  are  developed,  is  destitute  of  uephridia  in  tlie  adult, 
and  contains  priuiaril"  the  sui)i-aoesopliageal  ganglion  of  the 
nervous  system  (Fig.  Ml,  ce),  the  ganglia  of  the  trunk  meta- 
nieres  (n)  lying  ventrally  to  the  digestive  tube;  while  the  tail 
segment  bears  the  anal  opening  and  usually  presents  other 
characteristics  which  distinguish  it  from  the  preceding  seg- 
ments.    It  is  rare,   however,  leaving  aside  this  antero-pos- 
terior  differentiation,  that  a  perfect  metameric  condition  is 
found  in   any  Annelid.      Secondary  changes   may  interfere 
with  the  similarity  of  all  the   metameres ;  a  suppression  of 
parts  usually  present  in  some  of  the  segments  may  occur,  as, 
for  instance,  where  the  reproductive  organs  are  confined  to 
one  or  two  metameres,  or  again  there  may  occur  a  differentia- 
tion of  the  anterior  appendages  for  a  special  function  where- 
by a  marked  dissimilarity  between  the  anterior  and  posterior 
metameres  is  produced.     Finally,  owing  to  peculiar  habits  of 
hfe,  the  metamerism  may  be  almost  or  completely  lost,  being 
indicated  only,  perhaps,  by  one  set  of  organs,  such  as  the 
nerve-ganglia,  or  else  only  evident  in  the  larval  stages.     Para- 
sitism  or  a  fixed  or  tubicolous  habit  of  life  are  among  the 
principal  causes  of  this  degeneration,  examples  of  which  will 
be  seen  later. 

In  consequence  of  this  degeneration  some  Annelids  pre- 
sent a  metamerism  of  a  lower  grade  than  that  found  in  such 
forms  as  the  Nemerteans.  Other  peculiarities  of  structure 
occur,  however,  which  serve,  together  with  the  indications  of 
metamerism,  to  mark  out  the  Annelid  type.  One  of  these 
peculiarities  is  the  occurrence  in  nearly  all  forms  of  a  series 
of  nerve-ganglia  along  the  ventral  nerve-cords  ;  this  feature 
i^-  of  course  a  part  of  the  metamerism,  but  it  is  not  usually 
marked  in  the  metamerism  of  the  nervous  system  seen  in 
lower  forms.  In  these  scattered  ganglion-cells  occur  all  along 
the  nerve-cords,  which  extend  backwards  from  the  brain, 
while  in  the  Annelids  these  scattered  cells  are  associated 
together  to  form  metameric  ganglia.  Another  peculiarity  is 
fonud  in  the  structure  of  the  nephridia.  These  are  no  longer 
m  all  cases  rows  of  perforated  cells  closed  at  the  inner  end 
by  a  flame-cell,  but  may  consist  of  more  or  less  convoluted 
tnhp.n  lined  by  ciliated  epithelium  and  open  as  a  rule  into 


i 

5 


204 


IN  \  Kli TKnitA  TK  MOUPUOLOU  Y. 


the  cMoloin  by  a  wiilt^  l'miiu>l-lik(>  dxirornify.  Provision;*! 
ki(lll(^vs  of  tlio  Tiirbollarijiu  ty[)o  oinuir  in  tlie  liirvir  of  injui\ 
Annolids,  but  tho  iio[)hri'li<i  of  tho  udnlt  ure,  as  a  riilc!,  of  tlic 
cliaractor  just  iiulicatod  and  depart  widely  from  tho  Turb«'l- 
larian  character.  In  the  tliird  phice  tiio  reproductive  organs 
a»e  devoh>pod  in  the  i)oritc>iioal  lining  of  the  Cddom  ami  are 
not  usually  (except  in  the  Hirudinoa)  provivlod  with  siiecial 
dm'ts.  When  mature  the  ova  or  Hpermatt)zoa  are  simpiy 
shed  into  the  C(elomic  cavity  and  u>ake  their  way  to  the 
ext«M'ior  through  the  ordinary  nei)hridia,  or  through  nephridi-ii 
MptH'ially  nu)ditied  for  Hie  pur})ose.  Fii.iilly  it  may  be  mem- 
tionetl  that  a  blo(«d  vascular  system  is  usually  preseut. 


I.  Class  riiii>to|MMla. 

The  Olnetopoda  are  Anuelids  in  which  the  external  t^eg- 
mentation  of  the  boily  corresponds  with  the  internal  seg- 
mentation of  the  organs,  and  which  bear  along  tho  sides  of  the 
body  two  rows  of  pouches,  the  seta-sacs,  the  cells  lining  which 
Hocrete  chitinous  spicules  or  seta'  of  various  shapes,  which 
serve  for  the  purpose  of  locomotion  or  in  some  cases  consti- 
tute a  d(>fensive  armanuMit. 

The  class  is  ctinvenientlv  divisible  into  two  aubclasaes. 


Subclass  I.  POLYCHJETA. 

The  forms  iududeil  in  this  subclass  are  exclusively  ma- 
rine, and  are  characterized  by  the  presence  ou  tho  sides  of  a 
gr»>ater  or  less  number  of  the  i;i(>tameres  of  a  })air  of  hollow 
processes  of  tlu^  body-wall  ui>on  which  the  seta-sacs  occur 
and  which  are  known  as  pto'ttpoitia.  In  a  few  forms  {iSerpiiln) 
the  i^ara podia,  and  indeed  the  seta*  as  wi>ll  [I'oIi/i/ontiNs),  may 
be  al»s(Mit,  anil  in  others,  such  as  (Ij^nH'm'lla,  they  may  be  very 
nnu'h  reduceil  in  size,  but  as  a  rule  they  possess  a  higii  ile- 
gree  of  development.  In  its  typi«^al  form  a  parapodinni 
(^Fig.  08^  consists  of  a  iU)rsal  and  a  ventral  lobe  (>ach  of  which 
bears  s»»ta-sacs  ami  setoB  {s).  Towanls  the  base  of  each  lolit> 
there  may  fretjuently  be  found  a  slender  hollow  process,  the 
dorsal  and  ventral  cii'via,  {dc  and  ve),  and  j)late-like  or  more 
or  less  dendritic  appendages,  the  hrancliia'  (ftr),  either  modili- 


TYPK  ANNELIDA. 


205 


cutions  of  tho  cirri  or  bruiiclies  uriHing  from  tlioin,  and 
respiratory  in  function,  also  occur.  Muscles  puss  from  the 
l)()(ly-vvjill  to  tin;  piirai)o(lia,  which  thus 
l)()(H)nio  important  organs  of  locomo- 
tion and  in  somo  of  the  actively  swim- 
ming species  assume  a  more  or  less 
flattened  ])late-like  form. 

Tli(!  hiiad  segment  is  generally  well 
d'fierentiatcul  from  those  which  succeed 
it,  l)(>,ing  destitute  of  parapodia  and 
setie,  and  as  a  rule  carrying  a  iiund)er 
of  appendages  sensory  in  fun(;tiou,  and 
being  likewise  usually  provided  with 
eyes.  The  cephalic  appendages  nun  ^''"-  ^«— T'AKAi'onnrM  <»p 
1  1        ,  1  ,,  L       L      f  •   "  Nereis  nrciiti. 

i)e  short    and    rather    stout,    formmi; 

what  are    termed  •/)(»/;>/    (lig.  100,  p),        ,/«  ^  ,io,sal  dmus. 
or  somewhat  longer  and  more  slender,  s  =  sciu'. 

forming  the  ('//t/  (r),  or  eveii  still  moit^         ""  =  ventral  cirrus, 
slcmler,  being  then  known  as  tentacles  {t). 

Tlui  body  is  enclosed  in  a  chitinous  covering  secreusd  by 
the  sul)jac(!nt  ectoderm,  here  known  as  the  hifpodermw  {Vifr, 
'.>;),  ////).  'V\\o.  musculature  of  the  body-wall  which  lies  bidow 
the  hypodermis  is  separated  from  this  by  a  basement-mem- 
lirane  and  consists  of  an  external  layer  of  cinndar  fibres  (rm) 
aiiil  a  subjaci^nt  layer  of  longitudinal  fibres  {hn)  which  is,  as 
.1  ruh),  interrupted  iu  the  iidd-dorsal  and  ventral  lines  and 
also  in  the  region  of  the  two  lobes  of  the  parapodia  so  as  to 
form  four  bundles.  Special  muscles  extend  from  the  bod}-- 
wall  to  the  base  of  the  seta-sacs,  and  fiirtheimorea  ]>Mir  of 
muscle-bands  cross  the  cavity  of  each  nnitamere,  in  typical 
cases  passing  from  the  lateral  regions  of  the  dorsal  surface 
downwards  and  inwards  to  be  inserted  into  the  v<mtral  bodv- 
wall  on  each  sid«>  of  the  median  line.  The  inner  surface  of 
the  longitudinal  musch^-layers  is  liniul  with  .^  layer  of  fx-ri- 
foiinil  rclls  which  ct)mpletely  enclose  the  codom  {<v)  of  eacdi 
metamcre,  being  rofliu'ted  upon  the  surfaces  of  the  dissepi- 
nients  wdiich  foruj  the  internal  partitions  between  adjacent 
metameres.  The  separation  of  the  cadomic  cavities  of  the 
metamores  is,  however,  rarely  perfect,  openings  occurring  here 


CO 


206 


INVERTEBRATE  MORPIIOLOO Y. 


we 


aud  there  in  the  dissepimeuts,  and  in  some  forms,  such  as  Capi. 
^e?/«,  anumber  of  the  dissepimeuts  may  at  the  breeding  season 
completely  degenerate  so  that  the  cavities  of  the  various 
metameres  concerned  become  perfectly  continuous.  The 
coelom  of  each  metamere  consists  in  reality  of  two  sacs  which 
are  folded  around  the  digestive  tract,  which  they  enclose, 
and  come  into  contact  with  each  other  above  and  below  the 
intestine,  forming  the  dorsal  and  ventral  irmenteries  (Fig.  <Jt), 
dm  and  um).  That  wall  ui  each  sac  which  lines  the  muscula- 
ture of  the  body-wall  is  termed  the  somatic  layer  of  the  peri- 
toneum,  while  that  surrounding  the  digestive  tract  is  the 
splanchnic  layer. 

The   blood  vascular  system    consists   of   a  dorsal  vessel 
(Fig.  99,  dh)  which  ruus  along  the  mid-dorsal  line  of  the  diges- 
tive tract  and  which  is  frequently  contractile  in  portions  of 
its  course,  serving  as  a  heart,  and  a  ventral  vessel  {uh)  lying 
below  the  digestive  tract,  and  being  connected  with  the  dor- 
sal vessel  by  lateral  trunks,  arranged  metamerically.     From 
these  vessels  branches  are  distributed  to  the  various  regions 
of  the  body.     The  blood  is  frequently  colored,  usually  red, 
and  contains  colorless  corpuscles,  the  coloring-matter  being 
dissolved  in  the  plasma  in  which  the  corpuscles  float.     The 
blood  vascular  system  is  completely  closed  throughout  its 
entire   course,  never  opening   into   sinuses  without  definite 
walls.     In  addition  to  the  blood  which  circulates  within  this 
detinite  system  of  tubes  the  ccelom  also  contains  a  coipuscu- 
lated  fluid,  frequently  colored  and  ap{)r()aching  blood   very 
closely  in  its  chaiacters.     This  ha'mohjmph  contains  corpus- 
cles, usually  anujuboid  iu  form,  antl  may  circulate  tiuough  the 
body  from  one  metamere  to  another  through  oj)enings  in  the 
dissepimeuts.     In  a  few  forms,  such  as  Copifclht,  it  may  fulfil 
the  functions  of  the  blood,  a  true  blood  vascular  system  being 
wanting,  and  in  this  case  contains,  iu  addition  to  the  colorless 
amtcboid  corpuscles,  others  which  are  disk-shaped  and  pig- 
mented.    It  seems  proba])hs  however,  that  the  absence  of  a 
true  blood  vascular  system  is  a  purely  secondary  ])henonie- 
non,  aud  accordingly  does  not  indicate  a  i)rimitive  condition. 
The  mouth  is  Bituated  oii  the  ventral  surface  of  the  body, 
at  the  junction  of  the  head  metamere  with  the  flrst  truiik 


TYPE  ANNELIDA. 


207 


metamere,  and  leads  in  many  forms  into  a  strongly  muscular, 
usually  protrusible  pharynx  provided  with  chitinous  teeth. 
Upon  the  pharynx  follows  the  usually  straight  intestine  which 
opens  to  tho  exterior  at  the  jjosterior  extremity  of  the  body. 
In  Oapitella  and  the  allied  genera,  as  well  as  in  certain  mem- 
bers of  the  family  Eunicidao,  an  accessory  intestine  lies  veu- 
trally  to  the  principal  one,  into  which  it  opens  either  both 
anteriorly  and  posteriorly  or  else  anteriorly  alone.     This  ao- 

dh 


um      uh  r 

Fia.  99.— DiAGiiAM  OF  Thansvkrhe  Section  of   Annelid  (combination  of 

tlKures  by  Lano  aiul  Khlkrs). 


br  =  bmiu'hia. 

0  =  cirrus. 
em  =  circuliir  muscles. 

CO  =  caloin. 
db  =  dorsiil  blooil-vossel. 
dm  =  dorsal  imisentery. 
hy  =  hypodcrinis 


i  =  intestine. 
Im  =  lonj^iiudinnl  niu.scles. 
ne  =  uepliridium. 
ov  =  ovary. 
p  =  parapodium. 
lib  =  vi'htrul  blood  vessel. 
m;m  =  ventral  niesentery. 


UH  =  ventral  uervo-cord. 

oessory  intestine  is  ciliated  and  seems  never  to  contain  food- 
matter ;  it  has  been  considered  to  be  respiratory  in  function 
and  seems  to  be  a  special  development  of  a  ciliated  gioove 
which  runs  along  the  ventral  surface  of  the  intestine  in  cer- 
tain  other  forms.  Pouch-like  outgrowths  of  the  intestine  are 
frecjuently  present  and  may  sometimes  become  essentially 
glanduhir  in  function.  In  Ilesione  and  in  certain  species  of 
SiiUis  pouches  communicating  with  the  anterior  part  of  tho 


208 


IN  VMHTEliliA TE  MOliimOLOa  Y. 


«     * 


digostivo  tract  occur,  which  normally  are  filled  with  air  ;iiid 
aro  richly  supplied  with  Idood-vesselM ;  they  may  bo  respira- 
tory ill  fiuictiou,  ami  liave  been  compared  to  the  swim-bladder 
of  tish(^s. 

The   nervous  system  is  well  dovoloj)ed   in   all  Pidychiet.i, 
and  consists  of  a  sKpr(ia>soph(i(jc<(l  ganglionic  mass  situated  in 
the  head  segment,  fre(|uently  presenting  a  division  into  s(n- 
oral  lobes.     From  it  various  nerves  arise  passing  to  the  an- 
terior  segment,  and  in  addition  a  strong  cord  passes  from  it 
ventridly  on   eith(>r   sid(>  of   the  (x>sophagus  to   unite  with  a 
gaiiglion  lying  below  the  (i'soi)hagus  in  the  second  metamore, 
fi)rming  the  circiiiiucsop/Kiijnd  c()mini.s.snr('.     To  the  suha-Nop/Kt. 
(ji'dl    tjaiKjIlou    of    tlu^    second    nu^tamere    there    succeeds    a 
pjiir  of   ganglia  in    each  nn^tamere,  each    pair    being  united 
with  the  prec(>iling  and  succetMling  pairs  by  two  longitudinal 
cords  of  nerve-hbres,  the  ran iicrf Ives,   the  whole  constituting 
the  ventral  m*rve-chain,  and  furthermore  the  ganglia  of  each 
pair  are   united  by  a  transverse   commissure.     The   ventral 
uorve-chain    has    therefire   a  distinctly    ladder-like    arrange- 
ment, freipiently  somewhat  obscured,  however,  by  the  api)roxi. 
mation  of  the  ganglia  of  each  pair  and  a  consecpient  shorten- 
ing of  tlu>  traiisv(>rs(>  commissures.     From  the  v.irioiis  ganglia 
nerves  arista  which  pass  to  the  musculature  of  the  metam(>res 
and  to  the  hyptxlermis  and  its  stMisi^-organs.     In  the  major- 
ity of   forms   the    nervous   system    Ii»>s  freely   in  the    co'lom 
surrouml  ■  I   bv  a  special   sheath,  but  occasionally  in   various 
forms  widely  separattMl  g(Mietically  from  one  another,  such  as 
/'olj/iftti'i/im  and  the  Opheliaceio,  it  presents  a  })rimitiv(^  char- 
acU-r    in    being    completely    imbedded     in    the    hvpod(>rmis, 
rei'.dling    the    condition    in   ciMtaiu    Nemerteans   and    in   the 
Cniilaria.     Special   nerves  arising  from  the  sui)ra(est))thageMl 
ganglion  are  supplied  to  the  walls  of  the  digestiv(>  trai't,  form- 
ing the  so-called  sfonittfoifttNtrii'  nerves. 

Sense-organs  of  various  kinds  are  of  fr(H]uent  occurrence 
at  ditVerent  ])ortions  of  the  body  of  tlu^  Polyclneta.  In  addi- 
tion to  the  cephalic  and  caudal  cirri  which  are  richly  supplied 
with  nerves  and  are  presumably  tactile  in  function,  eves  are 
of  very  general  occurrence.  Thev  are  nsiiiilly  sit!i:ited  on  the 
heatl,   sometimes    iu    connection    with    the    hypoilermis   and 


TYPE  ANNELIDA. 


2()» 


soinetiniea  imbedded  in  the  dorsal  surface  of  the  brain.  For 
tho  most  part  they  consist  of  a  cu})  of  pigment-cells,  in  which 
numerous  sensory  cells  are  ])resent — a  lens  being  in  soiimj 
instances  developed  above  each  eye.  Occasionally,  however^ 
as  in  the  pelagic  genus  Alciope,  the  eyes  reach  a  high  grade 
of  development.  In  some  forms  they  are  not  confined  to  tin* 
region  of  the  head,  as  for  instance  in  the  genus  Pohjophthdhum 
— so  named  from  the  fact  that  pairs  of  eyes  are  found  on  the 
sides  of  a  number  of  the  trunk  mctameres  ;  in  the  majority 
of  tubicoious  Annelids  eyes  are  found  in  considerable  num- 
b.;rs  upon  the  branchial  lobes  of  the  head  sej^mrnt,  <"lie  genus 
Vermilui  possessing  somewhere  in  the  neighborhood  of  11,000 
separate  ocelli  in  this  region.  These  eyes  are  simply  differ- 
entiations of  the  ectoderm,  and  in  many  cases  an;  still  situated 
in  the  hypodermis  ;  they  consist  of  a  number  of  cells  which 
ar(!  prolongtul  at  their  inner  ends  into  a  nerve  filament,  while 
})eripherally  tht^ir  ])rotoplasm  is  converted  into  a  refractive 
substance,  each  of  these  cells  being  separated  from  its  neigh- 
bors by  pigment  deposited  in  its  peripheral  layers,  as  well  as 
by  a  number  of  smaller  pigment-cells.  On  account  of  this 
])igment-sheath  it  is  presunnible  that  each  of  these  optic 
elements  or  omniatidin  functions  more  or  less  independently 
of  the  rest,  and  the  eyes  are  to  be  considered  as  compound, 
composed  of  a  number  of  iudei)eudent  parts  each  of  which  is 
]>hysiologically  an  eye. 

Auditory  organs  or  otocysts  also  occur  in  certain  forms, 
but  cannot  be  considered  as  typical  of  the  Polyclneta.  In 
Arenicohi  they  consist  of  two  sacs  lying  in  close  proximity  to 
the  circunuesophageal  comnnssures  and  connected  with  the 
i^xterior  by  a  narrow  canal,  indicative  ot  their  origin  as  invag- 
inations of  tho  hypodermis.  The  walls  of  tiie  sack  are  formed 
by  columnar  cells  terminating  below  in  a  plexus  of  n«>rve- 
tihrils  and  covered  on  the  surface  turned  towards  the  cavity 
of  the  otocyst  with  a  firm  homogeneous  cuticle,  and  not  pos- 
sessing any  terminal  hairs.  In  the  cavity  a  varying  number 
of  spherical  particles  of  carbonate  of  lime,  the  otoliths,  are 
found.  In  some  forms  a  number  of  such  otocysts  are  present, 
as  iu  Aricia,  where  four  or  five  pairs  have  been  found  in  adult 


210 


IN  I  ■KliTKIiliA  TK  MOUrilOlAHl  Y. 


I 


iii(Hvi»limlH;  Iml.  in  tlio  majority  of  wpocioH  thoy  do  not  seem 
to  l>«  dovtilopotl. 

Ciliatotl    (lopn^HHionH   wliieh    liavo   beou   Hn[)i)OH(Hl  to   ho 
olfiu'tory  '  Hvt>  h.uMi  (IohciIIumI  jih  occuniiif,'  in   tlio  untorior 
rt>j'it»n  of  tli«^  Itotly  in  vjiriouM  HpooioH,  roiiching  n  high  «|«u'ol- 
opni.'ntm  l,ho  (\ipil,olIi,h,.,  wjioro  thoy  f,)rni  cIub-.shiip.Kl  hiicIch 
^«Hplll.K^  of  luMng  oviiKinjitod.      In  .uldition  th.uo  mo   to  bo 
f»)uiul  HCHttt>ivd  on  tho  Huifiu'o of  tho  body  niinuto hnlcn'-shapcd 
doprossions,  at  th.>  b.)lioni  of  which  uio  colls  boaring  long 
hairs  and  piosuniably  sensory  in   function  ;  and  fnithonuoro 
iu  a  fow  forms,  such  as  tho  Ca|)itolIida>  and  roliiophtlndrnm,  a 
Horios  of  sensory  hillocks  occur  along  tho  sidos  of  tho  body— 
a  pair  in  oach  motanu>ro,  f»)rming  tho  sniscoiyaiiN  of  ffic  la(eral 
litiv.     In  tlu'  Capitollidio  those  organs  aro  in  the  nntorior  mot- 
anuM-os  containod   in  doprossions,  hut  uioro  posteriorly  thoy 
{>r.>joct  slightly  from  tho  surface.     Tho  central   part  oi  oacli 
projection  is  retractile  and  is  formed  of  a  number  of  hair-colls, 
oach  oi  which  is  in  coiin.>ctiou  at  its  inner  end  with  a  norvo' 
fibril.     No    little    interest    attacJies    io    those   organs,   which 
forcibly  recall,  both  in  thoir  structure  aud  distribution,  tho 
lateral  liiu>  organs  i>f  tho  lower  Vortobratos. 

The  nophridia  (Fig.  [)[),  m%  iu  typical  adult  fi)rms,  occur 
as  a  single  pair  in  each  motamoro  »»xcept  tho  two  terminal 
ouoa.  Kach  consists  of  n  usually  conti)rtetl  or  coiled  tube 
lined  with  colls  opening  by  a  funnel-shaped  mouth  int.)  the 
oa>Iom  oi  the  motamoro,  perforating  tho  dissepiment  between 
it  and  tho  next  metamero  in  which  tho  greater  portion  of  it 
lies  and  in  which  it  opens  to  tho  exterior  by  a  sniall  pore  sit- 
uatoil  on  tho  ventral  surface  oi  tho  body  at  tho  base  of  tho 
parap..dium.  It  is  rare,  however,  that  "any  such  motamerio 
regularity  of  arrangement  *)ccurs.  and  very  fretpiontlv  they 
become  retluced  to  a  small  number,  or  even  to  two  pairs  ;  in 
tho  tubicolous  forms  a  fow  pairs  are  frocpientlv  found  in  tho 
anterior  portion  of  the  body  much  larger  than  any  of  the  rest. 
In  aildition  to  their  original  excretory  function  thev  may  also 
serve  as  outlets  for  the  reproductive  elements,  and  income 
oases  become  specially  moditied  for  this  puri)ose  aud  lose 
their  original  function. 


TYPK  ANNELIDA. 


211 


Til  CapUt'Ua  only  one  pair,  thiit  of  tho  oiglith  motamorc,  bocomcs  con- 
voHdd  into  a  k<i"'<h1  (IikiI;  and  il.  i«  iiilorostiriK  to  nolo  thafc  in  this  samo 
Ht'KiiK'iit  11  (ruo  (^xcrotory  impliridinrn  jh  also  proHont.  Wliothor  this  iiidi- 
catoH  or  not.  tlio  ocournMico  oriKinaliy  of  more  than  one  pair  of  nephridia  in 
oacih  mt^taincro  roiiiaiiis  to  1)0  sciin,  but  it  is  interesting  in  connection  with 
what  occurs  in  tin;  Oli^ocliuita  (see  p.  Uail). 

Tho  io[)r()(luctivo  orf^ann  coiiHist  of  local  thickenings  of  tlio 
peritonoiil  opitlioliiun  (Fig.  5)1),  ov)  in  nioro  or  fower  of  the 
Hoginonts.  Tho  ovu  or  Hpormatozou  fall  when  ripo  into  the 
coiloniic  cavity  and  ])aHH  to  tho  exterior  hy  the  nephridia. 
With  very  few  exoeptionH  tim  rolychieta  are  bisexual. 

The  olassitication  into  smaller  groups  is  to  a  certain  ex- 
tent artificial  at  present,  and  does  not  profess  to  have  any 
phylogonetic  signiiicance.     Three  orders  may  be  recognized. 

1.  Order  Archiannelida. 

This  order  includes  a  few  forms  which  are  supposed  to 
])resent  more  primitive  structural  characteristics  than  the 
remaiiiing  Polychiets.  They  show  as  a  rule  but  indistinct 
traces  of  an  external  segmentation,  and  are  entirely  devoid  of 
either  parapodia  or  setio.  Tiuitacles  occur  at  the  anterior 
extremity  of  the  head  metamoni ;  but  no  other  appendages, 
such  as  cirri  or  branchiie,  occur.  The  norvous  systenj  is  im- 
bedded in  tho  hypodorniis,  and  tho  nephridia  an;  short  tubes, 
a  single  \v.x\v  occurring  in  nearly  (svory  segment.  To  this 
group  belong  the  genera  PohigonUns  and  FrotodriliLS. 

2.  Order  Errantia. 

In  this  order  are  placed  the  free-swimming  or  creep- 
ing Polychieta,  in  which  a  considerable  similarity  of  the 
various  trunk  motameres  occurs.  The  parajjodia  are  as  a 
rule  well  dev(doped,  and  occasionally  are  broad  and  2)late-liko 
in  adaptation  to  a  free-swimming  existence.  Brancliia;  are 
usually  found  on  the  dorsal  lobes  of  a  considerable  number 
of  parapodia;  the  head  is  distinctly  marked  off  from  tho 
trunk  and  may  bear  eyes ;  while  tlu^  anterior  portion  of 
the  digestive  tract  is  converted  into  a  protrusible  pharynx, 
UHu-ally  nrmoil  with  <.'hitiu<>.U8  teeth.  To  this  order  l)Ginng 
the  genera  Nereis  (Fig.  100),  usually  found  lurking  beneath 


GO 


212 


INVERTEBRA TE  MORPHOLOQ  T. 


•Jil 


stoues  during  the  day-time,  but  becoming,  in  some  species  at 
least,  free-swimming  at  night ;  Lepidonottts,  characterized  by 
the  possession  of  elytra  arranged  in  overlapping  series  on  the 
dorsal  surface ;  Diopatra,  which  forms  tubes  for  itself  by  glu- 
ing together  particles  of  foreign  matter;  and  Autolytus  and 
Syllis,  which  are  peculiarly  pelagic  in  habit,  as  is  also  Alciope, 
characterized  by  its  large  highly-organized  eyes. 

3.  Order  Sedentaria. 
This  ordor  includes  a  number  of  forms  which  manufacture 
for  themselves  tubes  of  various  substances— some  being 
merely  composed  of  particles  of  sand  glued  together  by  an 
adhesive  secretion,  while  others  consist  of  a  chitinous  sub- 
stance,  to  which  foreign  bodies  may  be  added,  or  even  of  car- 


FiG.   100,— Anterior 
End  op  Nereis  virena, 
c  =  cirrus. 
p  =  piirapodium. 

t  Z  tentacle  ^^^'     ^^^•~^'"P''"'<»''^    ornaia    (after 

Vehrill). 

bonate  of  lime.  Within  these  tubes  the  animals  permanently 
reside,  and  in  conformity  with  this  mode  of  life  numerous 
adaptations  of  structure  are  found.  The  head  is  usually  pro- 
vided with  a  number  of  loner  nirri  nnA  fViQ  l^voT^plj."—  „-.„  J_„  xu^ 

most  part  confined  to  the  head  region.     In  some  forms,  such 


TYPE  ANNELIDA. 


213 


as  Serpula  and  Sdbella,  plume-like  branchiae  supported  by  an 
axial  cartilage-like  skeleton  occur  upon  the  sides  of  the  head, 
and  numerous  eyes  may  be  found  in  the  hypodermis  of  these 
structures.  Parapodia  are  as  a  rule  but  slightly  developed, 
sometimes  being  entirely  wanting  though  the  setje  persist, 
those  of  the  lower  parapodial  lobe  being  usually  hook-like. 
The  protrusible  pharynx  with  chitinous  teeth  does  not  for  the 
most  part  occur.  Amphitrite  (Fig.  101)  lives  in  tubes  in  sand, 
while  Terebella  composes  tubes  by  gluing  together  particles 
of  sand.  In  Sahella  the  tubes  are  membranous  in  character, 
Avhile  Serjnda  manufactures  more  or  less  contorted  tubes  of 
carbonate  of  lime. 

Development  of  the  Poli/chceta.  —  An  important  feature  in 
the  development  of  the  Polychseta  is  the  occurrence  of  the 
Trochophore  larva.  A  typical  example  of  this  larva  is  to  be 
found  in  the  development  of  Polygordius ;  it  is  a  transparent 
organism,  haying  the  form  of  two  Ioav  cones  united  by  their 
bases  (Fig.  102).  Just  below  the  junction  of  the  two  cones  is 
the  mouth  (31),  leading  by  a  short  stomodmcm  or  oesophagus 
into  a  retort-shaped  stomach,  the  intestine  opening  at  the 
apex  of  the  lower  cone.  Above  the  mouth,  along  the  line 
where  the  two  cones  are  united,  lies  a  band  of  strong  cilia 
arranged  in  two  rows  and  forming  an  almost  complete  girdle 
for  the  body,  being  wanting,  however,  in  the  mid-dorsal  region. 
This  is  the  prototroch  (pro)  or  praeoral  band  of  cilia,  and  par- 

1  to  it  is  a  second  weaker  band  which  passes  behind  the 

.      th — the  paratroch  (po)   or   postoral   baud.      The   slight 

,    between  the  two  bands  is  lined  b}-  fine  cilia,  the  adoral 

Cilia,  and  in  some  Trochophores  a  band  of  fine  cilia  extends 

backwards  along  the  ventral  surface  of  the  body  towardo  the 

apex  of  the  lower  cone. 

At  the  apex  of  the  upper  cone  is  a  strong  thickening  of 
the  ectoderm,  the  apical  plate  {ap),  which  is  nervous  in  function 
and  bears  a  number  of  strong  cilia  and  may  also  have  imbedded 
in  it  pigment-spots  which  function  as  light-percipient  organs. 
From  the  apical  thickening  four  nerve-cords  (w)  extend  back- 
wards, one  being  dorsal,  the  other  ventral,  and  the  remaining 
two,  stronger  than  the  others,  lateral.  A  series  of  fine  nerve- 
rings  arranged  concentrically  about  the  apical  thickening  unite 


214 


INVERTEBRA TE  MORPUOLOG  Y. 


these  cords  at  regular  intervals,  the  lower  riug  being  con- 
nected with  the  cells  which  bear  the  protrochal  cilia  and 
forming  the  prototroch  nerve. 

At  the  apex  of  the  lower  cone  and  ventral  to  the  intestine 
lie  two  cells,  or  two  masses  of  small  cells,  which  constitute  the 
mesoblasts  and  give  rise  to  two  longitudinal  mesoblast  bands 
{mb).     A  few  scattered  cells  are  also  found  between  the  ecto- 


FiG.  102— Tkochophoke  of  Polygohdius  (after  Hatschek). 

■4  =  fiuus.  mb  =  inesoblast-baiid. 

ap  =  apical  plate.  ne  =  uepliridiiim. 

M  -  luouth.  pro  =  prteoral  band  of  cilia. 

m,  m',  m"  =  muscles.  po  =  postoral  band  of  cilia. 

derm  and  the  digestive  tract,  some  of  which  elongate  and  be- 
come muscle-fibres  (w),  and  which  have  been  thrown  off  from 
the  mesoblast  bands.  In  some  forms  a  band  of  muscle-fibres 
underlies  the  prototroch  cells.  In  the  neighborhood  also  of 
the  mesoblast  bauds  in  the  posterior  cone  there  occurs  on 
either  side  of  the  digestive  tract  a  small,  sometimes  branched, 
tubular  body,  the  head-kidney  (ne).  Each  kidney  consists  of 
a  row  of  perforated  cells,  terminating  in  a  funnel-shaped 
structure  closed  at  its  mouth  by  a  cell,  the  whole  structure 
thus  agreeing  closely  with  the  uephridia  of  the  Platyhelminths. 
From  such  a  larva  the  adult  condition  is  derived  bj'  the 

gradual   elongation  of   the  posterior   part   of   the  body an 

elongation  wHh  Avhich  the  mesoblast  bands  kepn  nanp    i^lie 
mesoblasts  retaining  their  position  at  the  posterior  extremity^ 


TYPE  ANNELIDA. 


215 


and  continually  adding  to  the  bands  by  the  formation  of  new 
cells.     The  bands  as  growth  proceeds  break  up  into  a  n    mber 
of  masses,  the  mesoblastic  somites,  in  the  interior  of  which 
cavities  appear,  and  adjacent  pairs  of  masses  growing  dorsally 
and  ventrally  finally  come  into  contact  above  and  below  the 
digestive  tract,   the  dorsal    and   ventral    mesenteries  of   the 
intestine  being  thus  formed,  and  later  a  metamerization  of  the 
body-wall,  corresponding  with  that  of  the  mesoderm,  also  takes 
place.      The  anterior  cone  of  the  larva,  which  at  first  sur- 
])assed  in  size  the  posterior  one,  gradually  becomes  smaller, 
aud  the  prototrochal  cilia,  and  in  some  cases  the  cells  also,  are 
thrown  ofi".     The  apical  plate  takes  i)art  in  the  formation  of 
the  supracje.sophageal  ganglion  of  the  adult,  aud  the  lateral 
nerve-cords  arising  from  it  form  the  circumoesophageal  com- 
missure, becoming  connected  with  thickenings  of  the  ventral 
hypodermis  arranged  metamerically  and  representing  the  ven- 
tral chain  of  ganglia.    The  head-kidneys  gradually  disappear, 
being  merely  provisional  larval  structures,  and  now  nei)hridia 
of  the  Annelid  type  develop  from  the  mesoderm  of  the  trunk- 
metameres. 

Altliough  the  Trocliophore  larva  occurs  in  the  hfe-history  of  many  of 
the  Annelids,  as  well  as  in  other  groups  as  will  be  seen  later,  yet  never- 
theless it  is  not  invariably  present.  In  some  forms  a  single  l)and  of  Iar<'e 
cilia  runs  around  the  middle  of  the  body,  whicli  is  elsewhere  uniformly 
ciliated,  while  in  others  the  cylindrical  larva  is  surrounded  by  several 
I'iiiids  of  cilia  succeeding  one  another  at  definite  intervals.  In  certain 
siK'cies  the  larva  is  provided  with  very  long  sette  which  are  thrown  off 
(iiiriiig  larval  life,  and  are  interesting  on  account  of  similar  setis  having 
))('en  found  in  fossil  forms,  though  absent  in  recent  adult  species. 

It  is  also  worthy  of  note  that  in  some  forms  the  Trocliophore  larva  is 
succeeded  by  a  well-marked  stage  in  which,  in  addition  to  the  head  seg- 
ment, three  trunk  segments  are  developed.  It  is  possible  that  this  may 
represent  an  ancestral  form  from  which  certain  other  groups  have  taken 
tiieir  origin. 

In  what  may  be  considered  exceptional  cases  a  non-sexual  rci)ro- 
duction  by  budding  also  occurs.  In  the  genus  Protnla  a  zone  of  growth 
occurs  in  the  sixteenth  segment,  and  at  this  point  later  separation  takes 
place,  a  new  head  developing  for  the  po.sterior  individual  from  the  ori.rjual 
seventeenth   segment.      In    one   species    of   Syllis    the    new   individuals 


arise   not   only  in   a  linear  series   but  al 
brandling  colony  is  produced  raniifviiig  tl 


IIyalos{ 


ion 


so   as   lateral   buds,   .sn   t!;at 
irough  the  canal  system  of  iIk* 


00 


ge  in  which  the  form  lives.     The   buds  eventually  separat 


e  as 


216 


INVEHTEBHATE  MOliPlIOLOG  Y. 


sexually  mature  male  and  female  individuals  wliich,  since  they  differ  fr<jni 
the  parent  form  in  possessing  more  highly  developed  eyes  as  well  as  a 
more  perfect  adaptation  of  the  parapodia  for  swimming,  probably  leave  tin; 
sponge  and  swim  about  freely  in  the  ocean  distributing  their  sexual  elements. 
If  this  be  the  ease,  this  species  presents  both  colony  formation  and  alterna- 
tion of  ^'enerations,  the  latter  phenomenon  being  also  manifested  by  other 
si)e(;ies  of  SylUs  and  by  Aiitolytus,  in  which  buds  are  produced  linearly, 
ditfering  from  the  parent  in  the  structure  of  the  parapodia  and  separating 
to  lead  a  free  existence  as  male  and  female  individuals.  A  modification  of 
this  process  is  found  in  certain  species  of  Nereis,  in  whidi  at  the  time  of 
sexual  maturity  the  posterior  segments  of  the  body  develop  seta?  more 
l)erfectly  adapted  for  active  locomotion  by  swimming  than  were  those  of 
the  immature  form  ;  these  sexually  mature  forms  were  at  one  time 
referred  to  a  separate  genus,  Heteronereis. 

The  Phylngeny  of  the  Polychaia.—The  origin  of  the  Polychwta  has  been 
within  recent  years  the  subject  of  considerable  discussion.  The  discovery 
of  the  wide  distribution  of  the  Trochophore  larva  led  to  the  supposition 
that  it  was  an  ancestral  form,  from  which  the  Polycha>ta  had  been  de- 
veloped by  a  process  of  linear  budding,  each  metamere  of  the  Polyclia-t 
body  being  equivalent  to  the  original  Trochophore  and  the  adult  organism 
being  a  co-ordinated  succession  of  Trochophore  individuals.  Other  authors, 
however,  who  do  not  see  in  metamerism  the  result  of  a  budding  of  tlie 
individual,  but  rather  the  multiplication  of  its  subordinate  parts,  are  in- 
clined to  refer  the  Annelids  to  a  Nemertean-like  ancestor  and  to  consider 
the  Trochophore  larva  a  purely  secondary  adaptation.  Between  these  two 
views  it  is  difficult  to  decide,  and  it  is  possible  that  in  their  plain  statement 
neither  is  quite  correct,  though  each  may  contain  certain  elements  of 
truth. 

It  seems  exceedingly  probable  that  a  larval  form  which  is  met  with  in 
the  life-history  of  the  Annelids  and  Mollusca,  as  well  as  in  a  modified  form 
in  other  groups,  has  some  ancestral  significance.  It  is  difficult  on  any 
other  hypothesis  to  explain  its  occurrence  in  widely  different  groups,  since 
it  seems  hardly  probable  that  it  coidd  have  arisen  independently  in  scver.il 
instances.  Convergent  evolution  could  hardly  be  carried  to  such  an  ex- 
tent as  to  produce  in  the  Mollusca,  quite  independently  of  any  genetic 
relationships,  a  larva  resembling  in  all  its  structure  that  of  an  Annelid. 
If  the  Trochophore  occurred  only  in  the  Annelids,  it  might  be  quite  po.ssible 
that  it  had  made  its  appearance  in  the  life-history  of  some  primitive 
Annelid  as  a  secondary  modi lication  of  a  more  priniitiv(>  larva,  and  had 
reappeared  subsequently  in  the  life-history  of  all  forms  descended  from  thi.s 
Annelid  ancestor,  but  this  would  not  explain  its  occurrence  also  in  the 
Mollusca,  unless  it  be  supposed  tliat  the  members  of  this  group  have  been 
derived  from  the  primitive  segmented  Annelid,  a  view  that  has  little  to 
recommend  it.  Tlie  working  of  the  biogenetic  law  (see  p.  143)  is  interfered 
with  in  innumerable  instances,  and  the  distinguishing  between  examples  of 
its  action  and  secondary  modifications  is  the  most  difficult  task  of  the 


TYPE  ANNELIDA. 


217 


cmljryologist.  The  evidence  at  present  available  seems,  liowever,  to  point, 
in  the  case  of  the  Trochophore,  to  its  being  an  example  of  the  law,  and  to 
tliis  extent  the  first  of  the  two  views  stated  above  is  probably  correct. 

But,  on  the  other  hand,  this  may  not  be  the  case  with  the  second  part 
of  the  theory.  If  the  view  as  to  tlie  origin  of  metauieri.sui  which  is  advo- 
cated in  this  work  be  correct,  then  the  Annelid  cannot  be  regarded  as 
having  '  risen  directly  by  a  prucess  of  reproduction  by  budding  of  the 
Trochophore.  It  is  not  a  colony  uf  Trochophore  individuals,  but  a  single 
elongated  Trochophore  whose  organs  have  undei'gone  repetition,  producing 
a  high  grade  of  metamerism.  To  this  extent  the  second  of  the  views  may 
bo  correct,  but  this  does  not  necessarily  imply  that  the  Annelids  are  to  be 
derived  from  a  Nemertean-like  form  in  which  the  metamerism  is  not  quite 
so  perfect.  Metamerism,  as  here  explained,  is  simply  the  following  out 
into  the  higher  individualities  of  the  phenomenon  of  discontinuous  growth 
or  reproduction  by  division  which  characterizes  the  cell,  and  it  is  quite 
])ossil)lo  that  there  may  be  no  more  genetic  connection  between  the  meta- 
merism of  the  Nemertean  and  that  of  the  Annelid  tiian  there  is  between 
tiiat  of  the  Cestode  and  that  of  the  Nemertean.  It  may  have  arisen  cpute 
independently  in  the  two  forms,  and  in  fact  when  the  details  of 
metamerism  are  examined  in  the  two  groups  considerable  differences  are 
to  be  seen. 

The  view  here  advocated  in  regard  to  the  origin  of  the  Polychaita  may 
be  briefly  expressed  as  follows  :  The  Polych«ta— and  with  them  the 
Annelida  in  general— have  had  for  their  ancestor  a  non-metamenc  form 
of  ivhieh  the  Trochophore  is  the  hirval  represe)itntim,  and  this  in  the 
course  of  its  decelopment  elongated,  the  elongation  being  accompanied  by 
tht^  repetition  by  a  budding  process  of  certain  organs,  a  high  grade  of 
iiu'tanierization  being  thus  produced. 

The  relationships  of  the  Trochophore  seem  to  be  with  the  Turbellaria. 

The  nervous  system,  consisting  of  the  apical  thickening  and  lateral  nerve- 

ords,  is  very  similar  to  that  of  Turbellaria,  and  also  it  is  interesting  to 

notice  the  similarit^y  of  structure  of  the  head-kidney  with  the  Turbellarian 

nephridium.     The  exceedingly  small  development  of  the  parenchyma  is 

(tfobably  a  secondary  condition,  and  the  presence  of  an  anus  is  an  im- 

poitant  advance  upon  the  Turbellaria.     An  undoubted  similarity  in  many 

respects  exists  between  the  Rotifera  and  the  Trochophore,  and  the  former 

have  been  regarded  as  persistent  Trochophores  or  else  as  forms  descended 

from  the  Trochophore.     This  latter  view  in  one  of  its  phases  has  already 

l-een  considered  (p.  195),  and  an  important  difference  in  the  relation  of  the 

MipracKsophageal  ganglion  to  the  prototroch  mentioned.  Reasons  have  also 

been  given  for  the  belief  that  the  Rotifera  are  descended  from  Turbellarian 

ancestors,  and  it  seems  probable  that  the  line  of  descent  of  the  Rotifers 

was  identical  for  a  time  with  that  followed  by  the  Trochophore    the 

former  group  branching  off  from  it  shortly  before  the  Trochophore  ancestor 

Biade  Its  appearance  on  tiie  scene.     In  this  respect  the  Rotifers  and  the 


")| 


218 


INVERTEBRATE  MORPIIOLOG  Y. 


gl 


Troclophore  are  related  to  each  other,  but  hardly  with  so  close  an  afflniiy 
as  would  be  implied  by  a  statement  that  they  are  persistent  Trochophoros. 

II.  Subclass  Oligoch^eta. 

The  OHgoclipeta  are  with  few  exceptious  fresh-water  or  ter- 
restrial ChtBtopods,  aud  present  a  much  simpler  body  form 

thau  do  the  Polycha^ts.  The  first 
segmeut  or  prchstomiuiu  (Fig.  10;j, 
pj')  is  devoid  of  tentacles  or  cirri, 
aud  ouly  iu  a  few  forms  are  eyes 
present  upon  it.  The  body  is  divided 
into  well-marked  segments,  but 
parapodia  are  lacking,  though  in 
the  majority  of  forms  setfe.  arranged 
iu  a  more  dorsal  (s')  and  a  more 
ventral  is)  group,  occur  on  the  sides 
of  each  metamere  ;  in  a  few  forms, 
however,  a  single  series  of  groui)s 
only  is  present,  while  iu  PerichtvUt 
the  setio  are  arranged  in  a  rim: 
around  each  metamere,  and  in  Amt- 
chvta  they  are  Avanting,  their  place 
being  indicated  only  by  the  sacks 
in  which  in  other  forms  they  are 
Fio.  103.-ANTEmonENuoF  ^evehuied  and  which  project'  into 
Liiiiibrkiis  ,,  ,  ,  ,  ,  , 

the    c(elom    as    large    hypodermal 

glands.  As  a  rule,  too,  no  branchim 
are  pr^sent,  the  blood  being  aerated 
through  the  walls  of  the  body,  mi- 
nute brancdies  of  the  blood-vt'ssels 
»  -  iaictal  MctiP.  i)enetrating  into  the  hypod<M-nns  in 

nl  =  opc'iiiiig  of  viis  deferens.    tlu>  terrestrial  forms  ;  a  few  aberriint 

forms,  however,  possess  either  dnrs;d 
or  ventral  {(]ha'tnhr<inchm)  appendages,  which  are  probably 
respiratory  in  function,  on  many  of  the  segments,  while  in 
the  genus  Dero  the  ting(U-like  })rt)ce88eH  of  the  terminal 
metamere  are  probably  brarudiia\ 

Tlu^  exterior  of  the  l»ody  is  covered  by  a  well-marked  cuti- 
cle, and  beneath  it  lies  the  ectoderm  or  hypiHlvrmin,  usually 


C  =  clitelluin. 
gl  =  glands. 

m  —  nioiill'. 

od  =  openinj:  of  oviduct 
pr  =  prosloiniuni, 

D  =  ven  trill  setOB. 


rich   iu 

cells  CO 

pass  cei 

ing  to  t 

the  ant 

thicker 

structur 

ilerinisi 

to  this,  ] 

terrui)te 

sides.    I 

nients   c 

body,  ai 

jieritone 

reflected 

ing  a  do 

<piently 

nients  ai 

various 

with  eac 

nients  ni 

one  8ej)a 

curs.     O 

towards 

the   (lor.s 

segment 

comniuni 

ii.'iry  cin 

change  1 

lymph,   t 

through 

I'ountl  SOI 

detach   tl 

ill  the  hit 

I'asionall 

furrow  w 

and    imm 

seem  to  1 

tain  extei 


TYPE  ANNELIDA. 


219 


nch   lu    glaiHl-eells   ami   also   contaiuiug  numerous*  sensory 
oells  coniiected  at  their  inner  ends  with  slender  fibrils  vvLick 
pass  centrally  und  unite  Avith  others  to  form  nerve-cords  pass- 
lUK  to  the  ventral  nerve-cord.     In  some  of  the  segments  near 
he  anterior  portion  of  the  body  the  hypodermis  is  usually 
thicker  than  elsewhere  and  richer  in  ghxnd-cell.s,  forming  a 
•structure  known  as  the  clitellum  (Fig.  103,  c).    A\'ithin  the  liypo- 
der.nis  is  a  usually  thick  layer  of  circular  uuiscles.  and,  internal 
to  this,  longitudinal  muscles  whose  continuity  as  a  layer  is  iu- 
terrupted  at  the  dorsal  and  ventral  mhl-liues  as  well  as  at  the 
sides.    Muscular  dissepiments  divide  the  ccelom  into  comi.art- 
laents   corresponding   to  the    external    segmentation    of   the 
body,  and  the  various  compartments  are  lined  by  a  layer  of 
pe.it,>neai  cells  which  along  the  dorsal  and  ventral  lines  is 
reflected  towards  the  digestive  tract,  which  it  surrounds,  form- 
ing a  dorsal  and  ventral  mesentery.     The  former  of  these  fre- 
<piently  disappears,  as  may  also  the  ventral  one.    The  dissei.i 
inents  are  rarely  perfect,  being  usually  perforated  so  that  the 
various  ccBlo   ,ic  compartments  are  placed  in  communication 
with  each  other,  and  in  rare  cases  a  number  of  the  dissepi- 
ments  may  be  wanting,  as  in  ^;o/o.s-o,,m,  where  but  a  single 
one  separating  the  head  from  the  trunk  c.elomic  spaces  oc- 
curs.    On  the  median  dorsal  line  of  more  or  fewer  metameres 
mvanls  their  posterior  edge  a  sn.all  opening  usuallv  occurs 
the   ,hrsal  pore,    and    similar    pores    are  found  in  the    head 
.segment  ot  some  forms.     They  place  the  c<.domic  cavitv  in 
coniniumeation  with  the  exterior,  but  do  not  seem  under  .'.rdi 
imry  circun.stances  to  be  the  n.e,-,„s  of  any  extensive  inter- 
change between  the  external  water  and  th'e  ccelcndc  luemo- 
v-'.pl.     though   occasionally  this   httter  fluid   may  And  exit 
l.n.ugh  then..     Annmg  the  peritoneal  cells  are  usually  to  be 
•-..H    some  which  enclose  greenish-brown  particles  and  n.av 
.!.■  uch  then.selves  fron,  th.  peritoneal   layer  and  float  about 
'"  fl'<^  liMMuolyniph,  eventually  dying  and  .lisintegratin.^     Oc- 
J-Msionaily  these  chlor,uj.,jn,-  rrlh  ure  specially  aggreg.tTd  in  a 
l-m,u  which  runs  along  the  dorsal  surface  of  the  intestine 
"'"I    1  in  mediately   sum. und    tlm   dorsal    bhiod-vesHrl 
seem  to  be  excretory  in  fund 


II 


tjii 


n  (>> 


ion,  performing  perhaps  t 


xteut  the  part  of  the  liver-cells  of  the  Vertebr 


<)  a  cer- 


ata. 


220 


IN  VEIi  1  'EBRA  TE  MOIiPlIO  L  0  G  Y. 


A  circulatory  system  is  always  preseut,  aud  consists  of  a 
dorsal  lougitudiual  vessel  lying  on  the  dorsal  surface  of  the 
digestive  tract  and  a  veutral  oue  lying  below  it,  the  two 
being  united  in  more  or  fewer  of  the  metameres  by  one  or 
two  lateral  vessels  ou  each  side.  The  dorsal  vessel  is  con- 
tractile, the  blood  in  it  flowing  towards  the  anterior  extremity, 
and  the  lateral  vessels  are  also  usually  contractile.  Branches 
are  giveu  off  to  the  muscles  and  to  the  various  organs  in  reg- 
ular metameric  succession,  and  additional  longitudinal  vessels 
are  also  found  accompanying  the  ventral  nerve-cord,  two 
lateral  and  one  ventral.  In  the  terrestrial  forms  tine  branches 
l)enetrate  into  the  hypodermis,  the  aeration  of  the  blood  being 
thus  effected  in  the  absence  of  special  branchire.  'ilia  blood 
in  the  majority  of  forms  is  red  from  the  })resence  of  hjenio- 
globiu  dissolved  in  the  plasma  and  contains  colorless  cor- 
puscles. As  in  the  P(^lychieta  the  c(elom  contains  a  hfcnio- 
lymph  in  which  corpuscles  tloat. 

The  digestive  tract  forms  a  straight  tube,  extending  from 
the  mouth,  situated  on  the  ventral  surface  at  the  junction  of 
the  prostomium  and  tirst  trunk  metamere,  to  the  terminnl 
anus.  The  mouth  opens  into  a  short  mouth-cavity,  and  this 
into  a  more  or  less  muscular  pharynx,  which  in  most  cases 
can  be  protruded  from  the  mouth  and  is  slung  to  the  body- 
wall  by  numerous  radiating  muscular  bands.  To  it  succeeds 
a  smaller  (esoi)hagus,  which  communicates  posteriorly  in  ter- 
restrial forms,  after  in  some  cases  dilating  to  form  a  sack-like 
thin-walled  crop,  with  a  muscular  ijizzord.  The  intestine 
which  succeeds  this  is  usually  somewhat  pouched,  being  con- 
stricted in  the  regiou  of  the  dissepiments  and  bulging  out 
into  the  intervening  cadomic  cavities.  In  the  terrestrial  Oli- 
gt)cluets  its  absorptive  surface  is  increased  by  the  projection 
into  it  along  tlu^  dorsal  surface  of  a  longitudinal  fold,  ilie 
tiiphlosnU;  the  chloragogue  cells  lying  in  th(*  furrow  |)roducTd 
by  the  fold.  Various  glands  open  into  the  digestive  tract  iit 
dill'ereut  regions,  as,  for  instance,  salivary  glands  which  optn 
into  the  anterior  part  of  the  (I'sophagus  in  some  forms,  and 
calciferouH  glands  (Morren's  glands)  which  contain  jjartich  s 
of  cinbouate  of  lime  and  arc  found  opening  into  the  (Ksoplia- 
gu8  in  terrestrial  forms. 


TYPE  ANNELIDA. 


221 


The  nervous  system  consists  of  a  supi-aoesoplia«,'e!il  ^^an- 
gliou  (Fig.  lO-A,  ce)  of  a  somewhat  complicated  structure  lying 
in  the  anterior  portion  of  the  body.  In  ^^o/osow(t  it  is  "con. 
nected  with  the  hypodermis  (i.e.,  the  ectoderm),  but  in  most 
forms  it  lies  upon  the  anterior  part  of  the  digestive  tract,  quite 
separate  from  the  hypodermis.  It  differs  in  position  from 
the  corresponding  ganglion  of  the  Polyclupta  in  that  it  is  not 
usually  situated  iu  the  anterior  metamere  or  prostomium,  but 
has  passed  farther  back  and  may  lie  in  the  second,  third  or 
fourth  metamere  or  even  more  posteriorly.  It  sends  off  nerves 
to  the  sensitive  i)rostomium  and  gives  rise  to  two  connnis- 
sures  which  pass  backwards  and  downwards  on  either  side  of 
the  pharynx  to  unite  with  the  suboesoi)hageal  ganglion  (.so), 
which,  like  the  brain,  is  formed  of  two  more  or  less  fused  lat- 
eral masses,  each  of  which  in  many  forms  shows  indications  of 
being  compound  and  formed  by  the  fusion  of  two  or  more 
ganglia  {Lumbricns).  To  this  there  succeeds  in  each  meta- 
mere a  pair  of  ganglia  each  of  which  is  united  to  its  i)rede- 
cessor  and  successor  by  a  pnir  of  connecting  cords,  the  whole 
ventral  cord  (??)  so  produced  having  a  characteiistic  ladder- 
like  arrangement.  Usually  the  connecting  cords  are  closely 
ujiproximated,  and  the  same  may  be  the  case  with  the  gan- 
glion pairs,  the  whole  being  ensheathed  iu  connective  tissue 
so  that  the  cord  seems  to  be  single.  From  each  pair  of  gan- 
glia  in  LuinhrirxH  three  nerves  pass  out  on  aach  side,  the  two 
posterior  ones  being  closely  related  so  as  to  ajjpear  to  be  one. 
Nerves  especially  connected  with  the  digestive  ti-act,  the 
sloiiiafo(/n.sfrw  nerves,  seem  to  be  present,  but  their  distribu- 
tion and  connections  have  not  yet  been  thoroughly  studiiMl. 
in  some  aquatic  forms  a  hferal  nerve  imbedded  in  the  hvpo- 
dermis  and  united  anteriorly  with  the  supradisophageal 
ganglion  runs  along  the  lateral  line  between  the  two  rows  of 
setie,  recalling  the  lateral-line  nerve  of  the  Capifeflhhv  anion"'- 
the  l*olychu'ta. 

Sejise-organs  of  various  kinds  are  present.  T(  ntucles  are 
absent  throuj^^hout  the  group,  and  in  only  a  few  fc.rins  {Nais) 
<1()  eyes,  consisting  of  pigment-spots  imbedded  in  the  hypo- 
tlermis,  occur.  Ciliated  dp]tiT5Ssi«»iis  at  the  side  of  tini  pro- 
Ktomial  segment  occur  in  J'Jithmvna  and  a  few  other  genera, 


00 

5 


222 


ly  VERTEBIiA TE  MORPIIOLOG  Y. 


while  tactile  set*  or  impilht-  are  scattered  over  the  body.  lu 
those  forms  which  possess  a  lateral  nerve  seuso-orgaus  re- 
sembliug  those  of  CapiteUa  occur  metamerically  along  it,  and 
iu  the  geuus  Slavina  are  increased  in  number  so  as  to  form  a 
circle  of  from  fifteen  to  twenty  papilla  surrounding  each 
metamere  and  innervated  by  a  branch  from  the  k.eral  nerve. 
Cup-shaped  organs,  supposed  to  be  gustatory,  occur  especially 
abundantly  on  the  prostomial  metamere. 

The  excretory  system  has  usually  a  typically  metameric 
arrangement— a  single  pair  of  coiled  tubules  lying  in  each 
metamere.  Each  tube  opens  by  a  ciliated  funnel  into  one 
cuilomic  compartment  and  then  passes  backwards,  perforatiug 
the  dissepiment,  into  the  next  succeeding  compartment  in 
which  the  coiled  portion  lies,  aud  opens  to  the  exterior  in 
this  metamere  between  the  dorsal  and  veutral  rows  of  seta'. 
The  lumen  of  the  coiled  portion  of  the  tubule  is  intracellular, 
the  tubule  cousisting  in  this  region  of  a  series  of  perforated 
cells  recalling  the  condition  found  in  the  Platyhelminths.  In 
a  certain  number  of  anterior  metameres  the  nephridia  may 
be  wanting  in  the  adult  condition,  though  in  younger  stages 
provisional  nephridia  are  to  be  found  in  these  metameres 
later  disappearing. 

Considorublo  variation  is  to  bo  found  in  tlio  noplwidial  systi-ni  of  (Ik; 
Oiigocliu'ta,  sonic  of  Uio  variations  siiKj^'cstin,-?  important  tlicon'tical  fon- 
sidcrations.  A  /aw/-/.vV///r// similar  to  that  dcscnhed  as  occnrrint,'  in  tliu 
Troehoplioro  larva  persists  in  ilin  adult  staj,'(>  in  somo  Olijroclia-tarand  in 
Ctenodtilas  appears  to  bo  tho  only  nophridiuni  which  oxists.  In  othoi' 
fonns,  suoh  as  C/i(rfoi/<i.sfer,  the  ontiro  nephridia!  system  is  coin|)osod  of 
tubules  having  a  deeided  similarity  to  the  head-kidney  in  the  intracellular 
character  of  the  luii.«en,  and  in  the  al)sence  of  any  ciliated  funnel,  the 
iinier  end  of  tii<f  lubido  bciuK  closed.  Furthermore  the  ceils  enelosinK  Hio 
canal  are  in  addition  perforated  by  numerous  minuter  braneliinj,'  canals 
which  open  into  tiio  central  linnen.  This  fact  siiirKcsts  the  ("mipicto 
homology  of  the  nephridial  sysleni  throughout  the  entire  body  notwith- 
standing the  usual  marked  histological  distinction  between  "the  head- 
kidneys  aud  the  nephridia  of  the  trinik  metameres.  There  seems  little 
reason  to  doubt  that  the  Oligochu'ta  have  been  derived  from  the  Poly- 
chu'td,  and  the  nephridial  system  in  the  two  forms  is,  therefore,  homol- 
ogous.    It  must,  therefore,  be  possible  for  a  nephridiinn  with  an   intra- 

nnllilliii'  i>iiiiiil   lit  till  <  i-.i  n.!!',  .Kill. 1.1  i>>l,.  ,,!>..  it,  ...I.:..!,  4i._  _„,-     i    •      •     .  .,     , 

- ' '"''  '!!!<•  Oil*,  iii  iVimii  liii; canal  is  nitorceiiiiiai'. 

The  nephridia  of  ('hatnijuder  are  uiupiestionably  homologous  with  tlioso 


TYPE  ANNELIDA. 


223 


of  Lumbrieus,  for  instance,  whicli  possess  a  terminal  funnel,  and  are  like- 
wise similar  in  structure  to  and  may  be  regarded  as  repetitions  of  the 
head-kidney,  thus  establishing  the  homology  between  the  two  forms  of 
nephridium. 

In  carrying  the  homology  of  the  Annelid  nephridium  back  to  that  of 
the  Platyhclminth  the  question  arises  whether  it  is  equivalent  to  the  whole 
branching  system  of  the  Turbellarian  or  only  to  a  part  of  it.     Whichever 
view  of  metamerism  be  taken  the  various  nei)hridia  of  tlie  Annelids  arc  to 
be  regarded  as  bud-products,  and  each,  therefore,  equivalent  to  a  branching 
Turbellarian  nephridium.    It  has  been  suggested  that  the  Annelid  nejjhrid''- 
ial  system  has  been  produced  bj  the  fragmentation  of  an  originally  con- 
linuous  system,  but  for  this  there  is  no  ombryological  evidence.      Each 
nephridium  being  a  bud  from  an  undifferentiated  nephridial  blastema  is 
just  as  much  an  organ-individual  as  is  the  branched  nephridium  of  a  Tur- 
bcllarian -^ust  as  much  an  individual,  though  of  a  lower  grade,  as  is  the 
bud  of  a   Polyzoon   developed  from  an   undifferentiated   blastema.      It 
might   be  supposed,  then,  that   the  Annelid  nephridium   migiit  show   a 
branched  structure  in   certain  primitive  forms,  and  indeed  a  branched 
liead-kidney  occurs  in  Polychaet  Trochophores.     A  branched  condition  is 
however,  rare  in  the  trunk  nephridia,  though  it  does  occur  in  ccrt-.in  ter- 
restrial Ohgochajta  in  which,  however,  it  must  be  regarded  as  a  purely 
.secomlary  phenomenon  without  any  phylog,>netic  signiticance,  since  in  the 
development  of  such  nephridia  a  single  tube  's  first  formed  which  'ater  on 
bec.mes  solid  and  then  gives  off  the   branches,  the  various  nephridial 
branches   of  successive    segments    becoming   sometimes    united       This 
branched  condit.      passes  into  one  in  which  the  various  branches  separate 
aiHl  acquire  independent  openings  ;  several  pairs  of  nephridia,  four  in  the 
anterior  segments  of  a  .spedes  of  Perfc/uHa  and  a  greater  number  in  other 
lorms.  occurring  in  a  single  segment.     This  branching  ami  multiplication 
<>t  nephridia  is  confined  to  terrestrial  forms  which  in  their  conditions  of 
existence  are  farthest  removed  from  the  primitive  state,  and   it   is   not 
improbable  that  the  multiplication  bears  .some  relation  to  the  assumption 
01   a  terrestrial  m.uJe   of  life.     In   the  genus  Lnmhrica.s,  in  which  the 
nophridia  are  simple  coiled  tubes,  a  duplication  of  the  nephridia  in  some 
seoments  is  to  be  found.     The  reproduc.ive  ducts  are  probably  modified 
n.'plindia,  and  ...  all  aquatic  fo.-ms  other  nephridia  are  ab.sent   .n   the 
nu-ta,ne,.es  in  which  t hey  occu.-.     I„  /.o>,Ma,,^  however,  in.  for  ins.ance, 
..■  metamere  which  contains  the  oviducts,  two  pairs  are  p.-esent.  one  o} 
^^1";  '   nianis  its  original  excretory  function,  while  the  other  has  been 
"I'Mlilied  ...  t„nn  m  duct  for  the  reproductive  elements. 

The  leproclnctive  orKmii.s  Imve  a  very  .lifferent  arrui.oeineut 
iiom  what  iH  fouii.l  i„  the  Polydi.otn,  boiuj.  li...it.,l  to  a 
<'n...p,ir,itiv«ly  feu-  .u...t..i,npro« ;  aiKl  fnrthorinoiv  ii,,.  ()]i. 
K..ehM>ta  are  thr(,„^.h<,„t  horn.aphroditio,  tho  n.ah-  a.ul  fe.nale 


GO 

2 


224 


INVERTEBRATE  MORPHOLOGY. 


i 


organs  both  Ijiug  in  the  auterior  portion  of  the  body,  usually 
between  the  ninth  and  fourteenth  metameres,  or  sometimes 

even  farther  forward.  There  are 
either  one  or  two  pairs  of  testes 
(Fig.  104,  t),  which  arise  like  the 
ovaries  from  the  peritoneal  epithe- 
lium and  early  break  down  to  m 
grf-rt:»''  ..■/  !o«^'  extent,  their  cells 
p?  •— ,  'uto  seminal  vesicles  (t'.sj, 
whb  they  undergo  further  de- 
velopment into  spermatozoa.  The 
vasii  de/erentia  {vd)  are  moditied 
nepliridia,  and  are  either  two  oi' 
four  in  number  according  as  there 
are  one  or  two  pairs  of  testt?s. 
"When  four  are  present  they  nmy 
open  separately,  or  may  unite  in 
pairs  on  either  side  in  a  common 
atrium,  through  which  the}-  open 
to  the  exterior,  or  finally  those  of 


Fig.    104  —Nervous   Systkm    .,  .,  .,  ,      , 

AND  liKPRouucTivE  Okoanb  ^^]^  ^''^J^©  Side  may  unite   a  short 

distance  below  the  funnels,  f()rmiii<^' 


OF  IjUiubricus. 


n  —  ventnil  iiervecord. 
od  —  oviduct. 
ov  =  ovary. 

rs  =  leceptaciiliim  soiiiiuis. 
«o  =  suboesopliageul  ganglion. 

t  =  testis. 
vd  =  vas  deferens. 
vs  =  vesieula  .seniinalis. 


ee  -  siipracBsophageal  ganglion,    for  the  greater  part  f)f  their  course 

a  single  tube.  Tliere  is  only  a 
single  pair  of  ovaries  (ov),  to  which 
in  some  forms  ovarian  receptacles 
similar  to  the  seminal  vesicles  are 
addfHJ ;  and  in  all  but  some  of  the 
lower  forms  oviducts  {od),  which 
are  modified  nephridia,  are  ])res- 
ent.  In  front  of  the  metameres  which  bear  the  testes  one, 
two,  or  occasionally  three  pairs  of  invaginations  of  tlie  body- 
wall  occur,  producing  pouches  projecting  into  the  body-cavity 
—the  seminal  receptacles  (rs) — which  receive  the  seminal 
fluid  during  the  mutual  interchange  of  it  which  takes  place  on 
copulation. 

A  satisfactory  subdivision  of  tlio  Oligochajta  into  orders  has  :iot  yet 
bct'ti  possible  ;  indeed  the  various  fiuniiics  are  ao  rclutcu  to  one  .•uiotiiet' 
that  such  a  subdivision  .seems  unnecessary.     Formerly  it  was  tlu'  custom 


TYPE  ANNELIDA. 


225 


to  recogniie  two  orders,  Limicokv  and  Tenicolce,  aquatic  forms  being 
referred  to  t!ie  former,  and  terrestrial  ones  to  tiie  latter— a  division,  how- 
ever, which  is  decidedly  artificial.  Less  so,  but  still  unsatisfactory,  is  a 
division  into  Naidotnurplia,  reproducing  non-sexually,  and  Lumbrico- 
muipha,  reproducing  by  tlie  sexual  method  only.  It  seems  on  the  whole 
better  to  omit  a  subdivision  into  larger  groups,  and  recoguize  one  into 
families  only. 

Development  of  the  Oligochceta. —lu  the  development  of  the 
Oligochaita  there  is  practically  no  larval  stage,  but  a  sufficient 
amouut  of  uutiition  is  supplied  to  the  enibvjo,  either  in  the 
form  of  yolk  in  the  egj^-  itself  or  as  an  albuminous  substance 
stored  up  in  the  interior  of  a  cocoon  in  which  the  ova  are 
contained,  to  enable  it  to  pass  through  all  its  early  stages 
while  still  within  the  egg-shell  or  cocoon,  and  to  assume  a 
free  life  only  when  it  has  reached  the  form  of  the  adult.  The 
Trf)chophore  larva  under  such  conditions  is  useless,  and  is 
suppressed  in  the  ontogeny,  the  development  becoming  thus 
direct  or  of  the  foetal  type.  This  mode  of  development  has 
been  acquired  as  an  adaptation  to  the  aquatic  or  terrestrial 
life,  in  which,  for  obvious  reasons,  the  occurrence  of  a  free- 
swimming  larva  would  be  an  iucouvenieiice  rather  than  an 
advantage. 

In  the  Polychrpta  it  was  stated  that  usually  at  a  very  early 
stage  of  development  one  cell,  Liter  dividing  into  two,  differ- 
entiates from  the  rest  as  the  primary  mesoblast,  and  gives 
rise  to  all  the  mesodermal  tissues  of  the  adult"-  rm.  This  is 
an  example  of  a  precocious  segrcfjation  of  the  nn^sodtMinal 
material  into  a  single  cell.  It  is  to  be  presumed  that  in  more 
l)rimitive  forms  the  mesoderm  separated  off  from  the  eudo- 
derni  only  at  a  relatively  late  period  of  development;  the 
tender.cy,  however,  for  the  a))pearance  of  an  im;,ortaut  struc- 
ture to  be  thrown  farther  and  farther  back  in  the  individual 
development,  to  api)ear  at  successively  earlier  stages  in  the 
developmi  "f,  has  asserted  itself  to  such  au  extent  that  the 
mesoderm  in  the  Polychu'ta  makes  its  appearance  while  the 
embryo  is  still  composed  of  but  a  few  ceils,  becoming  there- 
fore segregated  in  a  single  cell.  Such  a  process  has  further- 
more the  ndvuntage  of  permitting  a  rapid  growth,  the  original 
embryonic  mesoblasts  retaining  their  position  at  the  posterior 


00 

2 


226 


INVERTEBRATE  MOItPHOLOOY. 


t 


I    : 


xe 


X  - 


eud  of  the  body  aud  giving  rise  by  division  in  a  transverse 
plane  to  rows  of  cells,  the  mesoblast  bands.  Such  a  pre- 
cocious segregation  of  the  mesoderm  also  occurs  in  the  Oli- 
gochaeta.  In  a  Lumhricus  embryo  there  may  be  seen  near 
the  posterior  extremity  of  the  body  the  two  mesoblasts  (Fig. 

105,  m),  lying  one  on  each  side 
of  the  middle  line,  with  the  meso- 
blast-bauds  {nib)  extending  for- 
wards from  them.  A  little  in 
front  of  them  and  on  either  side 
ma}'  be  seen  another  cell  {nh), 
giving  rise  to  a  band  extending 
anteriorly,  which  later  on  will 
become  differentiated  into  the 
ventral  nerve-cord,  the  cells  Avhich 
give  rise  to  it  being  neuroblasts ; 

Tr,«  Ac\K     «...  ^      \'?  r.      w^^^^®  ^  ^i^*^6  behind  and   exter- 

liQ.  105.— hunFACE  View  OF  Pos-       n      ,      ,, 

TEHioK  ExiKEMiry  OF  Embkyo  "''^^'>'  *°  th&iiQ,  on  either  side,  two 
OP  Ltimbriciis  (after  E.  B.  Wilson),  other  cells  (?ieaud  x)  occur,  giving 

rise  likewise  to  germ-bands,  whose 
further  fate  is  undecided,  though 
it  seems  probable  that  the  inner  of 
the  two  bauds  gives  rise   to   the 
nephridia,  the  cells  being  nephro- 
bJasts.    Thus  from  a  small  number 
of  cells  the  entire  nervous  system,  with  the  exception  of  the 
supraoesophageal  ganglion  (which  arises  as  a  local  thickening 
of  the  ectoderm,  comparable  to  the  apical  thickeniiigof  theTro- 
chophore),  the  nephridia  and  all  the  other  mesodermal  tissues 
arise,  the  precocious  segregation  of  these  organs  being  carried 
to  an  extent  only  equalled  in  the  Hirudiiiea.     Indications  of 
it,  however,  are  found  in  the  Polycha^ta,  not  only  in  the  meso- 
blasts but  also  in   a   layer   of   cells    occupying   the   ventral 
surface  of  the  embryo,  and  forming  the  so-called  ventral  plate, 
from  which  the  ventral  nerve-cord,  the  nephridia,  and  some  of 
the  musculature  seem  to  arise.     A  reduction  of  the  number 
of  cells  constituting  this  ventral  plate  to  the  smallest  number 
consistent  with  a  bilateral  symmetrv.  that  is   in  two.  for  each 


ec  —  ectoderm. 
m  =  inesobliist. 
mb  =  inesoblast-baud. 
nb  =  ueuiobliist. 
7ie  =  iiephrohlast. 
X  =  lateral  teloblast. 


TYPE  ANNELIDA. 


227 


ig- 


sei  o   structures  formed  from  it,  would  give  rise  to  a  condition 
sucli  as  is  found  in  the  Oligochseta. 

A  number  of  the  simpler  Oligochaets,  in  addition  to  repro- 
ducing in  a  sexual  manner,  also  reproduce  by  division,  and  in 
some  forms  it  plays  a  much  more  important  part  than  the 
sexual  method,  which  in  jEolosoma  is  not  yet  known  to  occur. 
In  the  simplest  form  of  this  method  of  reproduction  the 
animal  simply  divides  at  the  middle,  each  portion  after  sepa- 
rating regenerating  the  parts  which  are  wanting.  In  one  spe- 
cies of  Cfenodrilus  each  metamere  except  the  anterior  one 
may  separate  and  become  a  new  individual ;  a  phenomenon 
which  might  be  regarded  as  illustrating  the  bud  theory  of 
metamerism,  but  which  seems  more  properly  to  be  a  case  in 
which  the  gradual  integration  of  the  multiplied  organs  has 
reached  its  highest  development— the  case  standing  as  the 
culmination  of  the  process  of  metamerization  rather  than  as 
au  example  of  its  mode  of  origin.  In  Nais  a  division  of  the 
new  individuals  may  begin  before  they  have  separated,  and 
chains  may  thus  be  produced  composed  of  individuals  vary- 
ing in  the  stage  of  regeneration  which  they  have  reached, 
but  which  eventually  separate  and  may  later  become  sexually 
mature. 

As  might  be  expected  from  the  occurrence  of  this  mode  of 
reproduction,  the  power  of  regeneration  of  lost  parts  is  pos- 
sessed in  a  high  degree  by  the  Oligoch^ta ;  and  not  only  in 
those  forms  which  habitually  reproduce  by  division,  but  also 
iu  forms  like  Lumhricus,  in  which  under  normal  conditions 
this  method  of  reproduction  is  unknown. 

Affinities  of  the  OUf/ochata.—Tlniva  is  Utile  reason  to  doubt  that  the 
OlitrochaQtii  liave  ))eon  derived  from  the  Polychieta,  and  represent  members 
of  that  subclass  wliich  have  become  specially  adapted  to  aquatic  or  terrestrial 
modes  of  life.  A  few  OligocluTts.  such  as  Ifulix/nlns,  are  marine,  livinj? 
below  stones  between  tides;  but  tiiey  are  undoubtedly  derived  from  aquatic 
forms,  and  cannot  be  regarded  as  having  any  ancestral  significance.  As  re- 
gards the  more  definite  aflinities  of  the  group  little  can  at  present  be  stated 
with  certainty.  They  have  been  referred  to  forms  like  thv.  Capitellidse, 
in  some  of  which  the  parapodia  are  very  much  reduced,  as  is  likewise 
the  distinctness  of  the  head,  while,  as  in  the  Naids.  lateral-line  sense-organs 
are  present.  A  more  remote  relationship  through  the  Archiannelida  has 
also  been  suggested,  but  at  present  no  detiuite  evidence  is  forthcoming  as 
to  which  view  is  to  be  preferred. 


59 


"228 


INVERTEBRATE  MORPHOLOOT. 


It 


■ 


IP 


i^^ 

V 


II.  Class  Uirndinea. 

The  Hirudiuea  differ  from  the  CluDtopotla  iu  their  external 
form,  beiug  destitute  either  of  parapodia  or  seta?,  aud  possess- 
lug  at  the  anterior  end  of  the  body  a  muscuhir  sucker  at  the 
bottom  of  which  the  mouth  is  situated,  while  a  second  larger 
sucker  used  for  attachment  occurs  at  the  posterior  extremity 
of  the  body.  The  outer  surface  of  the  body  is  distinctly 
ringed,  but  a  comparison  of  the  rings  with  the  internal  organs 
shows  that  they  have  not  a  raetameric  value,  but  that  a  num- 
ber of  them,  varying  in  different  forms,  are  included  in  each 
true  segment  of  the  body.  In  Branchellion  and  Clepsine  three 
such  rings  correspond  to  a  metamere,  iu  Ichthyohdella  and 
Pontobdella  six,  in  Piscicola  twelve,  aud  in  all  the  group  of 
the  GnathobdellidfB  five.  Towards  the  anterior  and  posterior 
ends  of  the  b(.dy  a  reduction  of  the  uum  jer  of  rings  corre- 
sponding to  a  metamere  is  found,  as  for  instance  in  the  genus 
Macrohdella  (Fig.  106),  which  has  in  the  middle  region  five  rings 
to  a  segment.  The  first  two  metameres  consist  of  but  one  ring 
each,  the  third  of  two  rings,  the  fourth,  fifth,  aud  sixth  each 
of  three  rings.  At  the  posterior  end  of  the  body  the  twenty- 
third  metamere  consists  of  four  rings,  the  twenty-fourth, 
twenty-fifth,  and  twenty  sixth  of  two  rings  each  ;  while  prob- 
ably no  less  than  seven  metameres  whose  rings  are  not 
reailily  distinguishable  are  represented  in  the  posterior  sucker. 
The  entire  animal  consists,  therefore,  of  tliirty -three  metameres, 
■and  this  number  is  characteristic  for  all  the  Hirudin ea — a 
definiteuess  of  number  which  contrasts  strongly  with  the  wile 
variations  found  in  the  Chictopoda.  This  number  does  not 
include  a  sm.,'1  lobe  in  front  of  tlie  mf)st  anterior  metamere, 
which  may  be  equivalent  to  the  prostomial  lobe  of  the  Oligo- 
chfeta,  and  may  represent  another  metamere. 

As  iu  the  Oligochrota  the  gland-cells  of  the  hypoderrais  at 
about  the  time  of  reproduction  become  enlarged  and  more 
abundant  iu  a  definite  region  of  the  body,  forming  a  clitellum 
which  is  usually  in  the  neighborhood  of  the  tenth,  eleventh, 
aud  twelfth  metameres.  As  a  rule  no  brancliitc  occur,  though 
an  exception  is  found  iu  the    marine  genus  Branchellion,  iu 


TYPE  ANNELIDA, 


229 


which  each  ring  of  the  middle  region  of  the  body  bears  an 
appendage  which  functions  as  a  gill.  In  another  marine  form, 
PontobdeUa,  large  warts  occur  on  certain  rings,  which  prob- 


Fig.   106.  — Antkkiok  and  Pos- 
terior EXTHKMITIES   OP    Ma- 
crobdellu  senteriia  (afiei-  Whitman). 
an  —  alius. 

fo  =  opeuiug  of  oviduct. 
gc  ~  copulutory  glands. 
mo  =  opeuiug  of  vasii  deferentia 
oc  -  eyes. 

p  -  uepUiidial  pores. 
sp  =  seuse- papilla. 

1   100  =  anutili. 

i-xxv  =  meluiueres. 


ov-.n  vB        ^ 
Fig.    107.  —  Diagrams   to    show    Ar- 

KANGy.MENT  OF  Bl.OOU-SXNU.SKS  OF  (^4) 

Hirado,  (B)  Clepsine,  and  (C)  Nephelis 
(after  Bolhne). 

al  =  digestive  tract. 
c  =  ccelom. 
ds  -  dorsal  sinus. 
Is  and  Iv  =  lateral  sinus  or  vessel. 
n  and  mc  =  veuiral  neive-cord. 
7ie  =  nopliridiuui. 
ov  =  ovaiy. 
te  =  testis. 
m  =  veutral  sinus. 


ably  are  mainly  respiratory  in  function,  being  richly  supplied 
with  blood-vessels. 

^  The  exterior  of  the  body  is  covered  by  a  cuticle,  beneath 
which  lies  the  hypodermis.  The  muscular  tissue  which  nn- 
derlies  the  hypodermis  consists,  as  in  other  Annelida,  of  laj-ers 


CO 


230 


IJSf  VERTEBRA TE  MORPIIOLOG  Y. 


of  longitudinal  and  circnlar  fibres ;  and  in  addition,  between 
these,  a  layer  composed  of  fibres  which  cross  one  another 
obliquely  is  usually  present.  A  marked  distinction  from  what 
occurs  in  the  Cluetopoda  is  found  in  the  coelom,  which  in  the 
Hirudinea  is  traversed  by  a  parenchyma,  recalling  that  of  the 
Platyhelminths,  so  that  the  actual  cavity  is  to  a  great  extent 
obliterate!  and  the  dissepiments  only  to  be  distinguished  with 
difliciilty.  Those  portions  of  the  coelom  which  persist  (Fig. 
107,  Cc)  are  occupied  by  a  red  or  colorless  fluid  containing 
corpuscles  and  identical  and  continuous  with  that  found  in  the 
blood-vessels.  The  coelom  is  in  fact  represented  by  a  number 
of  blood-sinuses,  which  in  some  forms  are  lined  by  an  epithe- 
lium, while  in  others  such  a  lining  is  wanting.  On  account  of 
the  manner  in  which  the  blood-vessels  anastomose  with  the 
sinuses  it  is  exceedingly  difficult  to  distinguish  Avhich  spaces 
should  be  considered  as  belonging  to  the  circulatory  system 
proper  and  which  to  the  coelom — if,  indeed,  the  two  are  to  be 
considered  fundamentally  distinct.  As  a  rule  four  main  lon- 
gitudinal vessels  or  sinuses  are  to  be  found — viz.,  one  dorsal 
(Fig.  107,  (Is),  which  may  be  wanting  {Nephelis,  Fig.  107,  C)  and 
which  probably  corresponds  to  the  dorsal  vessel  of  the  Chiic- 
topoda ;  one  ventral  (vs),  sinus-like  in  character  and  frequent- 
ly destitute  of  an  epithelial  lining,  which  surrounds  the  ventral 
nerve-cord  ;  and  two  lateral  vessels  (Iv  and  Is)  unrepresented 
in  the  Chfetopods,  and  perhaps  also  to  be  regarded  as  rem- 
nants of  the  coelomic  cavity.  Communications  between  these 
longitudinal  vessels  occur  through  the  medium  of  smaller 
vessels ;  and  in  some  forms,  such  as  Nephelis,  the  connection 
between  the  lateral  and  ventral  vessels  takes  place  through 
ampullse,  globular  vesicles  arranged  in  two  pairs  on  each 
side  of  a  number  of  metameres  and  receiving  blood-vessels 
from  the  ventral  sinus,  while  other  vessels  passing  to  the 
main  lateral  vessels  arise  from  them.  In  many  forms,  espe- 
cially among  the  Gnathobdellidae,  a  rich  plexus  of  capillary 
vessels  penetrates  the  hypodermis. 

The  union  of  the  blood  vascular  system  with  sinuses  which  most  prob- 
ably represent  portions  of  the  ccelomic  cavity  suggests  an  intimate  relation, 
so  far  as  its  origin  is  concerned,  of  the  vascular  system  with  tlie  odRloni : 
and  this  view  is  borne  out  by  what  has  already  been  seen  to  occur  in  the 


TYPE  ANNELIDA. 


231 


^'^■ 


Nomerteans  p.  165),  the  lowest  forms  that  possess  a  distinct  blood  vascular 
system    In  th>s  group  the  co^lom,  so  far  as  it  exists,  consists  of  «„.all  space 
withou    any  definite  walls  scattered  through  the  parencliyma.     In  some 

Is      :  n        ""?'"■  ''''''"  —- -ates  with  these  spaces  thr  ugh 
«hich  the  blood  circulates,  it  being  only  in  the  most  highly  differentiated 

th  1.  that  the  blood-vessels  were  simply  coelomic  spaces  which  had  acquired 
dehn.te  walls;  and  it  seems  probable  that  such  has  been  their  on^-n  Jn  the 
Annelida  a  somewhat  different  state  of  affairs  occurs.  Here,  as  a  rule  there 
IS  a  definite  coelom  lined  with  peritoneum  and  completely  separated  from  the 
cavity  of  the  blood-vessels,  which  seem  to  represent  rather  the  rema  is 
of  an  original  cavity,  the  so-called  blastocoil  (see  p.  52)  which  Ins  be.,', 
almost  obliterated  by  the  growth  of  the  mesodermal  Lgment!^  the  holbw- 
mg  out  of  which  the  coelomic  cavities  have  been  formed  (see  p  56)  It 
seems  certain  that  the  ccelomic  spaces  of  the  Nemerteans  are  likewise  the 
remains  of  a  primitive  blastoecBl,  so  that  to  this  extent  the  homology  of  the 
blood-vessels  holds  in  the  two  groups. 

In  the  llirudinea,  however,  the  blood-sinuses,  if  they  are  coelomic  cor- 
respond wiHi  the  ecelom  of  the  Polych.ta  ;  and  furthennore,  in  '"01  ^o- 
luvts  and  Polych^ts,  as  well  as  in  the  Gephyrea,  as  will  be  seen  later,  the 
iuemolymph  contained  in  the  ea^lom  is  very  nearly  if  not  quite  identic.;!  in 
composition  w,th  the  blood  contained   in  the  blood-vessels.     These  facts 
would  .seem  to  indicate  a  close  relationship  between  the  Annelid  coelom  and 
.)e  more  primitive  blastoccBl;  or,  in  other  words,  would  lead  us  to  suppose 
at  theco^Iom  of  the  Annelids  lined  with  peritoneum  is  not  some  ling 
apai    and  distinct  from  the  blastocoel  cavity,  as  has  usually  been  supposed 
The  Mew  which  maintains  the  distinctness  of  the  two  forms  of  coelom  has 
Its  origin  in  the  fact  that  in  some  forms,  such  as  Sagitta,  a  ca^lom  lined  with 
pentoneum  is  formed  as  an  outgrowth  from  the  primitive  digestive  tract- 
and  It  ^^•i^s  supposed  that  all  coelomic  cavities  with  definite  walls  were  nri- 
marily  of  a  similar  origin,  and  hence  were  termed  enteroccels  in  contradis- 
tinction to  the  scMzocceh  or  simple  spaces  in  the  mesoderm  without  defl- 
»ite  walls,  which  are  in  reality  remnants  of  the  blastocoel.    The  significance 
of  true  enteroccels  will  be  discussed  later.    In  the  mean  time  1^  maybe 
pointed  out  that  there  is  no  embryological  evidence  in  favor  of  the  Annelid 

t,w     7'"!  '?''?'  '"  ''''''  '^  pouch-like  outgrowths  from  the  primi-  ' 

ne  chges tive  tract.     It  is  rather  to  be  regarded  as  a  schizoco^l  whose  char- 

.   ter  has  been  a  tered  by  metamerization,  and  by  the  manner  of  its  forma- 

lon  from  mesoblasts.     On  this  view  the  union  of  the  cavity  of  the  blood- 

essels  with  .he  c(^lom  in  the  leeches,  and  the  similarity  of  the  h^molymph 

to  the  blood  in  other  forms,  cease  to  be  morphological  puzzles. 

The  mouth  lies  at  the  bottom  of  the  anterior  sucker  pnd 
opens  mto  a  muscular  pharynx,  which  in  some  forms  (e  a  Clen 
sine)  IS  folded  similarly  to  that  of  some  Turbeilaria  (see  p  lU) 
so  as  to  form  a  protrusible  tube,  while  in  others  (e.g.  Hirndo 


S3 

s 


232 


INVERTEBRATE  MORPHOLOGY, 


i 


Fig.    108.— Diaqkam   of 

THK  EXCKKTOUY  Uk- 
I'HOUIICTIVK  AND  NeU- 
VtJUS  iSVHTKMS  OK  Iliiudo 
(iftcr    UoUHNK). 

■ce  =  ctMeldiil  giiiijfliou. 

ep  =  ('|)i(ii(lyiuu9. 

f/l  =  oviiluciil  gliiud. 

Ic  =  liiteral  blood-vessel. 

n  =  iK'pliridiii. 

i)V  =  oviiry. 

pe  =  i)euis. 

te  =  testis. 


Macrobdella)  it  is  thrown  iuto  three 
longitudinal  muscular  ridges  whose 
edges  may  become  converted  iuto 
chitin,  thus  forming  teeth.  Salivary 
glands  open  into  the  pharynx  in  some 
forms.  The  large  stomach  into  wliicii 
the  pharynx  opens  behind  gives  off  a 
number  of  lateral  pouches  (eleven 
pairs  in  Uirudo,  seven  in  Clepsine), 
sometimes  branched  and  increasing  in 
size  from  before  backwards,  the  most 
posterior  pair  being  usually  quite  long 
and  directed  backwards  parallel  to  the 
straight  narrow  intestine  which  opens 
to  the  exterior  on  the  dorsal  surface  of 
the  body,  just  anterior  to  the  posterior 
sucker.  Occasionally  onl}'  the  poste- 
rior pair  of  pouches  is  present,  and  in 
a  few  forms  they  are  entirely  wanting. 
The  nervous  system  (Fig.  108)  is 
constructed  on  the  ty])ical  Annelid 
plan.  It  consists  of  a  circunupsopha- 
geal  ring  and  a  ventral  nerve-cord 
composed  of  fibres  which  have  their 
origin  in  ganglion-cells  grouped  to- 
gether  at  definite  intervals  into  gan- 
glionic masses.  Several  of  these  gan- 
glionic masses  correspond  to  siuglo 
.segments,  but  at  the  anterior  and 
posterior  extremities  a  cousiderabh^ 
amount  of  fusion  of  the  metameiic 
groups  of  ganglia  has  occurred.  Tn 
Clepsine  phina  the  jiortiou  of  the  ner- 
vous system  which  lies  above  the 
ce80})hagus  consists  of  a  transverse 
band  of  fibres  passing  hiterally  into 
the     (iicunursophageal     commissures 


aiit 


1 


<ti 


a 


9 


lurnuer     oi     gaiigiioniir 
masses.     Six  of  these  latter  lie  in  front  of  the  band  of  tibros 


TYPE  AmfELIDA. 


233 


uud  correspond  to  the  metamere  formed  by  the  prostomial 
lobe.     Behind  the  transverse  band  are  four  additional  gangli- 
onic  masses,  apparently  forming  with  the  other  six  the  supra- 
iBSophageal  ganglion,  but  in  reality  forming  together  with  two 
additional  masses  on  the  ventral  side  of  the  nerve-cord  below 
the  cesophagus  the  ganglion  of  the  second  somite.     Immedi- 
ately posterior  to  the  two  ventral  masses  is  a  chain  of  eight 
ganglia  lying  one  behind  the  other  on  the  mid-ventral  line  of 
the  cord,  and  corresponding  to  these  there  occur  on  each  side 
along  the   dors*.l   surface   of   the  cord  other   eight  masses 
between  each  successive  pair  of  which  a  nerve  passes  out' 
There  are  therefore  four  metameric  ganglia  represented  in 
this   complex    structure,    each   cousisting   of    six   ganglionic 
masses  and  each  giving  rise  to  a  pair  of  nerves.     The  sub- 
a'sophageal  ganglion  accordingly  consists  of  the  ganglia  of 
four  metameres,  to  which   must  be  added  the   two  ventral 
masses  of  a  fifth  metamere,  the  supra-  and  subcesophageal 
ganglia  representing  together  six  metameric  ganglia.     Behind 
the  subcesophageal  ganglionic  aggregate  there  lie  twenty-one 
ganglia  separated  at  some  distance  from  each  other,  especially 
anteriorly,  each  one  representing  a  metamere  ;  and  finally  at 
the  posterior  end  of  the  body  is  anotlier  ganglionic  aggregate 
representing,  to  judge  from  the  number  of  nerves  arising  from' 
It,  seven  metameric  ganglia.     Thus  there  are  in  all  thirty, 
tliree,  or,  counting  the  ganglion  which  innervates  the  prosto- 
mium,  thirty-four,  metameric  ganglia— numbers  exactly  corre- 
spondiug  with  those  obtained  by  counting  the  rings. 

Tlie  sense-organs  of  the  hirudinea  have  especial  interest 
us  showing  an  atlaptation  of  what  may  be  considered  tactile 
sense-organs  to  a  different  purpose.     On  each  metamere  of 
the  body  in  all  Hirudinea,  with  a  few  possible  exceptions 
suiall  sensory  papilhe  (Fig.  lOG,  sp)  are  to  be  seen,  arran-o.l 
lu  cletinite  lines.     Tliey  occur  in  the  majority  of  forms  on  Uie 
Hrst  ring  of  each  segment,  though  in  some  species  of  N^pMis 
they  occur  on  all  the  rings.     On  th.^  dorsal  surface  of  each 
sensory  ring  there   are  three  papilhu  on   each  side  of   the 
iniddlo  lino,  and  the  same  arrnniroment  opf  iir^  on  the  v-nt  -  ! 
surface,  and  iu  addition  a  single  i)apiila   is   found""  a't   tL 
margin  of  the  ring  on  each  side.     There  are  thus  fourteen 


234 


INVERTEBRATE  MORPHOLOGY. 


longitudiual  rows  of  ijapilije,  six  on  the  dorsal  surface,  six  on 
the  veutral  surf>'ce,  and  two  marginal.  In  the  anterior  and 
posterior  segments  whose  width  is  reduced  the  marginal  pa- 
pillsB  may  be  wanting,  but  throughout  the  rest  of  the  body 
the  number  of  rows  is  constant.  In  structure  these  papilla? 
are  somewhat  complicated,  consisting  of  an  axial  bunch  of 
elongated  sensory  cells  bearing  fine  cilia  at  their  outer  ends, 
and  lying  in  the  connective  tissue  in  their  immediate  vicinity 
is  a  varying  number  of  large  cells,  each  containing  a  large 
watery  vacuole  in  the  interior,  the  nucleus,  in  consequence, 
being  pushed  to  one  side.  A  strong  nerve  runs  to  each  pa- 
pilla and  is  supplied  to  the  large  vacuolated  cells  as  well  as 
to  the  axial  sensory  cells. 

Slight  differences  are  to  be  found  in  various  forms  in  the  structure  of 
these  organs.  In  Clepsine  there  is  an  axial  bunch  of  hair-bearing  cells  to 
which  the  terminal  fibres  of  the  nerve  run,  and  posteriorly  and  Vjelow  the 
nerve  are  found  the  largo  vacuolated  cells.  In  Hirudo  and  NephtUs  no 
hair-bearing  cells  occur,  the  nerve  occupying  the  axis  of  the  organ  and  the 
vacuolated  cells  being  arranged  symmetrically  around  it^ 

It  is  probable,  in  view  of  the  two  kinds  of  constituent  elements  in  Clep- 
sine, that  in  this  and  similar  genera  a  double  function  is  possessed  by  the 
sensory  papillao,  the  hair-bearing  cells  having  perhaps  a  tactile  function, 
while  the  vacuolated  cells  are  visual.  It  seems  probable  also  that  primarily 
the  papilliB  were  similar  in  structure  and  function  to  the  orgaii.s  of  tln;^ 
lateral  line  of  certain  Polychif  ta,  such  as  the  (!apitellida%  or  perhaps  it  would 
be  better  to  compare  tiicMu  with  the  tactile  pai)illa3  of  certain  aquatic 
Oligocha^ta,  which  in  the  genus  8lavina  have  uti  arrangtmient  on  each  meta- 
mere  recalling  that  found  in  the  llirudinea. 

Towards  the  anterior  extremity  of  most  of  the  Hirudiuea 
a  varying  number  of  eyes  are  found.  In  some  s])ecies  of 
Clepsine  but  t\vo  such  organs  occur,  while  in  others  there  are 
six,  aud  iu  llirmlo,  MacrohleHa  (Fig.  10(5,  oc),  and  allied  foiius 
tlicre  are  always  ten.  In  the  latter  forms  the  eyt^s  are  always 
arranged  in  a  definite  manner:  one  pair  is  situated  on  the 
anterior  ring  (when  more  than  one  ring  occurs)  of  each  of  the 
five  metameres  immediately  following  the  prostomial  lobe, 
aud  if  their  position  be  determined  it  will  be  found  that  they 
occup3'  the  place  of  one  of  the  dorsal  sense-pupilhe,  tlie  eyes 
boing  serially  homologous  with  the  Hense-papillir  of  one  of 
the  dorsal  rows.     This  conclusion  is  verified  bv  their  struc- 


TYPE  ANNELIDA. 


235 


aH 


ture,  since  they  differ  from  the  sensory  papillae  only  in  the 
^'reater  number  of  the  large  vacuolated  cells  and  in  the  pres- 
ence of  a  quantity  of  black  pigment  in  the  surrounding  tissues. 
Other  sense-organs  somewhat  beaker-shaped  in  character 
411  e  found  upon  the  prostomium  and  have  been  regarded  as 
gustatory  in  function. 

JSephridia  occur  in  a  number  of  the  metameres  of  the 
middle  portion  of  the  body,  there  being  in  Hirvdo  (Fig.  108,  n) 
and  its  allies  seventeen  pairs.     Each  nephridium  has  a  ter- 
minal  funnel,  which  in   Glepsine  has  the   typical  Annelidan 
structure,  but  in  Hirudo  has  been  modified  so  that  the  inner 
extremity  of  each  nephridium  is  constituted  by  a  lobed  spongy 
ciliated  mass  without  any  definite  central  lumen.     The  funnel 
lies  in  a  blood-sinus,  either  the  ventral  one  as  in  Glepsine 
(Fig.  107,  B)  or  the  dorsal  as  in  Pontohddla,  or  in  a  sinus 
which  surrounds  the  testes  as  in  Hirudo  (Fig.  107,  A),  or  in 
a  special  sinus  which  is  to  be  regarded  as  a  coelomic  space  as 
in  Nephelis  (Fig.  107,  G).      The  canal  which  traverses  each 
nephridium  is  intracellular  as  in  the  Oligochseta,  and  in  some 
forms  minute  canals  traverse  the  substance  of  each  coll,  open- 
mg  into  the  central  lumen.     As  a  rule  the  various  nephridia 
are  quite  separate  and  distinct  from  each  otlier,  but  in  Pontob. 
deUa  and  one  or  two  other  genera  they  unite  to  form  a  net- 
work of  intracellular  canals   traversing  several   metameres. 
Immediately   before   their  exit  to   the    exterior  the   canals 
enlarge  in  some  forms  to  bladder-like  vesicles,  from  which 
a  short  tube  leads  to  the  exterior,  the  opening  being  situated 
either  upon  the  anterior  {Glepsine)  or  the  posterior  {Hirudo} 
ring  of  the  metamere  to  which  the  nephridia  belong. 

The  rei)roductive  organs  differ  from  those  of  the  Chieto- 
poda  in  possessing  ducts  which  do  not  seem  to  be  modified 
nephridia  and  which  are  continuous  with  the  walls  of  the 
ovaries  or  testes.  All  the  Hirudinea  are  hermaphroditic. 
The  ovaries  constitute  in  Glepsine  two  elongated  organs  which 
lie  in  the  middle  region  of  the  body,  expending  through  several 
metameres,  but  in  Hirudo  (Fig.  108,  or)  they  are  small  oval 
or  spherical  bodies ;  th«ir  ducts  dilate  to  form  a  uterus  auu 
finally  unite  to  open  on  the  mid-ventral  line  usually  in  the 
eleventh  metamere  (Fig.  lOG,  /o).     The  testes  (Fig.  108,  tt) 


236 


INVERTEBHA  TE  MORPHOLOO  T. 


consist  of  a  number  of  pairs,  varying  from  twelve  or  more  to 
six  {Clepsine),  of  spherical  bodies  lying  in  the  same  region  of 
the  body  as  the  ovaries.  Each  testis  has  its  own  duct,  which 
opens  into  a  longitudinal  vas  deferens  common  to  all  the 
testes  of  the  same  side  of  the  body.  Anteriorly  the  two  vasa 
deferentia  unite  to  open  in  the  mid-ventral  line  of  usually  the 
tenth  metamere  (Fig.  106,  mo),  frequently  through  a  strong 
muscular  penis  (Fig.  108,  pe).  In  many  forms  special  glan- 
dular thickenings,  supposed  to  be  useful  in  copulation,  occur 
on  the  ventral  surface  of  one  of  the  metameres  behind  that 
bearing  the  opening  of  the  oviduct  (Fig.  106,  gc). 

The  Hirudinea  are  at  present  usually  divided  into  two 
orders,  though  it  seems  probable  that  further  division  of  one 
of  them  will  be  necessary  later. 

1.  Order  GnathobdellidsB. 

In  this  order  are  included  the  leeches  which  are  provided 
with  chitiuous  jaws  in  the  walls  of  the  muscular  pharynx. 
In  addition  to  this  all  the  members  of  the  order  are  charac- 
terized by  possessing  five  rings  to  each  fully  developed  meta- 
mere. To  this  order  belong  the  Hirudinidee,  characterized  by 
possessing  ten  eyes  arranged  in  pairs  on  the  five  anterior 
metameres  behind  the  prostomium,  and  including  Hirido,  the 
medicinal  leech,  a  native  of  Europe,  instead  of  which  Macro, 
bdella  is  sometimes  used  in  America.  The  Nephelidifi,  with 
the  genus  Nephelis,  differ  in  possessing  fewer  eyes  (four  pairs), 
and  in  having  distinct  segmental  sense-organs  either  wanting 
or  occurring  on  all  the  rings  of  each  segment. 

3.  Order  Rhynchobdellidse. 

The  Rhynchobdellidro  are  characterized  by  possessing  a 
protrusible  pharynx,  as  well  as  by  possessing  three,  six,  or 
twelve  rings  to  a  metamere.  In  the  Ichtliyobdellidjo,  or  fish- 
leeches,  the  larger  numbers  are  found,  the  number  six  being 
characteristic  of  Pontoklella,  while  twelve  occurs  in  Piscicola. 
In  the  ClepsiuidjG  but  three  rings  are  found  to  each  meta- 
mere, and  the  eyes  are  either  two  or  six  in  number.  To  this 
family  belongs  the  genus  Clepsine,  a  conimuu  fresh-water 
form,  as  well  as  the  tropical  land-leech,  Hmnvnterin. 


TYPE  ANNELIDA. 


237 


Development  of  the  Himdinea.—The  Gnatliobdellid*  deposit  their  eggs 
in  chitinous  cocoous,  tm  do  tlje  Oligocliaeta,  and  the  development  is  of  the 
foetal  type,  in  coutradistiiictiou  to  the  larval,  the  ova  containing  as  a  rule  a 
considerable  amouui  of  yolk.  Ttie  mode  of  oviposition  of  the  majority  of 
the  Rhynchobdellid*  is  unknown  ;  but  in  the  genus  Clepsine  the  eggs  are 
fastened  to  the  veutral  surface  of  the  body  of  the  parent,  where  they  un- 
dergo development.  This  resembles  closely  the  development  of  Lumbricns, 
allowing  for  the  greater  amount  of  yolk  which  is  usually  present.  The 
same  precocious  segregation  uf  mesoderm,  nervous  system,  and  nephridia 
in  special  budding  cells,  the  mesoblasts,  neuroblasts,  and  nephroblasts,  i.s 
likewise  found,  and  lu  later  siages  the  mesoblast  is  distinctly  segmented 
and  coelomic  cavities  are  present,  which  later  become  to  a  great  extent 
obliterated. 

The  Affinities  of  the  Hirudinea.—lX  is  exceedingly  probable  that  the 
ancestors  of  the  Hirudinea  were  to  be  found  in  tha  Oligochffita,  the  two 
groups  having  not  a  few  structural  features  in  common.  The  embryologi- 
cal  peculiarities  found  in  the  two  groups  are  strikingly  similar ;  and  fur- 
thermore the  aquatic  or  terrestrial  habits  are  not  a  little  suggestive,  for 
although  some  leeches  are  marine,  nevertheless  the  majority  are  aquatic 
and  a  few  terrestrial.  The  complete  disappearance  of  parapodia  may  be 
considered  a  further  development  of  the  tendency  towards  their  oblitera- 
tion in  the  Oligoclueta,  where  only  the  setae  are  present,  these  even  having 
disappeared  in  the  Hirudinea  in  consequence  of  the  development  of  the 
suckers  and  a  new  mode  of  locomotion.  The  suggestive  arrangement  of 
tlie  sense-papilljB  of  the  Oligochaete  Slavina  has  already  been  mentioned. 

It  must  not  be  forgotten,  however,  that  the  differences  between  the  two 
groups  are  many  and  important.  Such  are,  for  instance,  the  disappearance 
of  the  original  coelomic  spaces,  the  communication  of  the  blood  vascular 
system  with  sinuses,  and  the  occurrence  of  special  ducts  for  the  reproduc- 
tive organs.  These  differences  have,  however,  equal  or  even  greater  im- 
portance when  (he  attempt  is  made  to  trace  the  Hirudinea  directly  to  the 
Polycha'ta,  and  it  seems  more  satisfactory  at  present  to  refer  them  back  to 
the  Oligoclueta. 


III.  Class  (jephyrea. 

The  Gepbyreans  coustitute  a  ji^roup  of  mariue  worms  wliii'li 
differ  from  the  CLujtopoda  principally  in  the  more  or  less 
coin])lete  absence  of  metamerizatiou.  All  trace  of  it  is  ab- 
sent upon  the  outside  of  the  body;  for  although  ^he  thick 
cuticle  may  be  marked  by  distinct  riugs,  these  bear  no  relation 
to  the  internal  parts  and  are,  as  in  the  Nematoda,  due  simply 
to  the  thickness  of  the  cuticle.  Ail  traces  of  parapodia  are 
lacking  in  many  forms,  while  in  others  they  are  representinl 


238 


INVERTEBRATE  MORPHOLOGT. 


0 


only  by  a  pair  of  setae  situated  on  the  ventral  surface  of  the 
body,  nearer  the  anterior  than  the  posterior  end.  The  body- 
wall  presents  a  close  similarity  in  its  structure  to  that  of  the 
Chsetopods — differing,  however,  in  the  occurrence  of  a  more  or 
less  pronounced  layer  of  fibres  having  an  oblique  direction. 
The  coelom  is  lined  by  a  layer  of  fiat  peritoneal  cells,  but 
shows  no  division  into  more  or  less  distinct  compartments,  no 
trace  of  metamerism,  but,  as  in  the  Chaetopods,  the  peritoneal 
lining  is  refiected  upon  the  walls  of  the  digestive  tract,  form- 
ing mesenteries  suspending  the  intestine.  As  a  rule  the  dor- 
sal mesentery  disappears,  and  in  some  cases  the  ventral  one 
is  almost  wanting,  the  intestine  being  slung  only  by  a 
number  of  irregular  strands  of  connective  tissue  extending 
from  it  to  the  body-wall.  In  some  forms  {Sipunculm)  the  sur- 
face of  the  peritoneum,  especially  that  covering  the  intestine, 
is  dotted  with  numerous  irregularly  scattered  minute  depres- 
sions, whose  openings  are  guarded  each  by  a  peculiar  ciliated 
cell,  and  which  contain  cells  comparable  in  function  to  the 
chloragogue  cells  of  the  ChaBtopoda.  The  coelomic  cavity  is 
occupied  by  a  haemolymph,  which  in  some  cases  is  colored, 
and  contains  numerous  cell-elements,  some  of  which  may  be 
circular  in  outline  and  colored  by  haemoglobin,  while  others 
are  amoeboid  and  colorless. 

A  blood  vascular  system,  principally  developed  in  the  an- 
terior portion  of  the  body,  is  present  and  appears  to  be  com- 
pletely closed,  though  connections  with  the  coelom  are  said  to 
exist  in  some  forms.  In  iSipuncithis,  for  instance,  the  system 
consists  of  a  collar  surrounding  the  a3sophagus,  sendiug 
braucLes  into  the  tentacles  which  surround  the  mouth,  aud 
tlorsally  dilating  into  a  wide  sinus  lying  just  below  the  brain  ; 
and  from  this  sinus  a  dorsal  vessel  (Fig.  109,  Bs)  passes 
backwards  along  the  digestive  tract  for  a  short  distance,  end- 
ing blindly  where  the  oesophagus  joins  the  stomach.  In  Echiu- 
rns  a  ventral  vessel  runs  the  entire  length  of  the  body  just 
above  the  nerve-cord,  and  it  is  united  with  the  dorsal  vessel 
by  lateral  vessels  at  its  anterior  and  posterior  extremities. 

The  digestive  tract  may  be  either  straight  {Priapulus)  or 
considerably  convoluted  {Echiurm  and  Siptinculus,  Tig.  109, 
Jilt),  and  the  anus  is  in  some  forms  terminal  {Echiuriui),  while 


TYPE  ANNELIDA. 


239 


in  others  the  intestine  bends  upon  itself  and  passes  forward  to 
open  on  the  dorsal  surface  near  the  anterior  end  of  the  body 
(Fig.  109,  A).  Throughout  the  greater  extent  of  the  intestine 
there  runs  along  its  ventral  surface 
a  ciliated  groove  which  is  no  doubt 
homologous  with  the  accessory  in- 
testine of  certain  Polychseta  (see 
p.  207). 

The  nervous  system  partakes  of 
the  absence  of  distinct  metamerism 
which  characterizes  the  other  parts. 
It  consists  of  a  brain  lying  in  the 
anterior  portion  of  the  body  above 
the  oesophagus  and  sending  a  com- 
missure downwards  and  backwards 
on  each  side  to  form  the  circum- 
cesophageal  collar.  These  two  com- 
missures unite  to  form  a  single 
nerve-cord  (Fig,  109,  n)  extending 
the  entire  length  of  the  body  in  the 
ventral  median  line,  differing  from 
the  ventral  cord  of  the  Chaetopoda 
in  the  absence  of  ganglia.  Nerve- 
cells  are  scattered  along  the  entire 
length  of  the  cord  and  are  not 
aggregated  into  special  ganglia, 
though  slight  indications  of  such 
an  aggregation  are  found  in  Priapu- 
lus.  Nerves  are  given  off  at  more 
or  less  regular  intervals  on  either 
.side,  a  somewhat  metameric  ap- 
pearance being  thus  produced,  but  ne  =  nepliridinm. 
the    corresponding    nerves  of    op-    ^*  =  a'soplmgus. 

posite  sides  do  not  invariably  arise   *^,!  "  '^'"^7\     . 

f ..^ ,     ,  1  -i  . ,  ,     -^  ,  vli  =  ventml  retractor  muscle. 

Horn  the  cord  opposite  each  other. 

One,  two  or  three  pairs  of  nephridia  (Fig.  109,  ne)  are  as 
a  rule  present  and  form  conspicuous  brown  tubes,  which  com- 
municate by  a  funnel  with  the  body-cavity  at  one  extremity 
and  with  the  exterior  of  the  body  at  the  other.    They  are 


Fig.  109.— SxnucTunE  op  8i- 
punculus  Qouldii  (after  An- 
drews). 

A  =  anus. 

Bs  =  blood  vessel. 

dR  =  dorsiil  retractormusclo. 

Lit  =  iiitcstiiie. 

N  =  nerve-coid. 


too 

s 


240 


INVERTEBRATE  MORPHOLOG  T. 


undoubtedly  homologous  with  the  nephridia  of  the  Chffitop. 
oda,  possessing  the  same  relations.  In  a  few  forms  {BonelUa, 
Phascolion)  a  single  nephridium  only  is  present.  In  addition 
to  these  in  Echiurus,  Thalassema,  and  allied  genera  there  is  a 
usually  much-branched  organ  on  either  side  lying  in  the  body- 
cavity  and  opening  into  the  terminal  portion  of  the  intestine. 
Numerous  ciliated  funnels  occur  upon  the  branches  placing 
the  organ  in  communication  with  the  body-cavity.  This  so- 
called  "  respiratory  tree  "  (so  named  from  a  supposed  homol- 
ogy with  the  similarly  named  organs  of  the  Holothuria  (q.  v.) 
are  probably  nephridia,  though  whether  or  not  they  per- 
form excretory  functions  is  not  quite  clear.  In  Priapulus 
these  organs  are  represented  by  branched  tubes,  the  branches 
of  which  terminate  blindly  in  flame-cells,  resembling  thus  the 
excretory  organs  of  the  Platyhelminths,  and  in  Sipunculus 
rudiments  of  these  organs  have  been  described  as  short  tubes. 

The  Gephyrea  are  bisexual,  the  reproductive  organs  {oc) 
forming  small  digitate,  elongate,  or  ovoid  processes  arising 
from  the  peritoneal  lining  of  the  body-cavity;  but  in  some 
forms  {Sipunculus)  their  products  early  escape  into  the  ca> 
lomic  cavity,  in  which  they  float.  The  exact  manner  in  which 
the  ova  and  spermatozoa  escape  to  the  exterior  has  not  been 
definitely  ascertained  for  the  majority  of  forms,  but  it  seems 
probable  that  the  nephridia  serve  as  the  generative  ducts. 
In  Priapulus  the  "  respiratory  trees  "  are  said  to  give  rise  to 
the  reproductive  organs,  and  also  to  serve  as  the  reproductive 
ducts — a  behavior  which  would  render  exceedingly  probable 
the  supposition  that  they  are  modified  uepliridia. 

Two  orders  are  recognizable  in  the  Gephyrea. 


1.  Order  EchiuresB. 
The  Echiureae,  sometimes  known  as  the  Gephyrea  armatu, 
are  characterized  by  the  presence  on  the  ventral  surface  ui 
the  body,  in  front  of  the  openings  of  the  nephridia,  of  a  pair 
of  setffi— the  genus  Echiurm  possessing,  in  addition  to  these, 
two  circles  of  setse  at  the  posterior  extremity  of  the  body. 
The  anus  is  terminal  in  all  the  known  species,  and  the  ter- 

branched  respiratory  trees.     The  anterior  end  of  the  body  is 


TYPE  ANNELIDA. 


241 


prolonged  into  a  prostomium  of  considerable  size  overlying 
the  mouth ;  it  may  be  short  and  broad  as  in  ^chiunts,  more 
elongated  and  slender  as  in  Thalassema,  or  deeply  bifurcated 
at  the  extremity  as  in  JBorteUia. 

A 


Fig.  IIQ.—Bonellia  viridis  A,  Adult  Female  opened  so  as  to  show  thb 
PRINCIPAL  OuGANa ;  B,  male  much  enlarged  in  proportion  to  the  female 
(trom  Hebtwiq). 

c  =  cloaca  m  =  muscles. 

d  -  rudimentary  intestine.  s  =  proboscis. 

g  =  lespiiatory  trees.  a  (in  Fig.  B)  =  spermatozoa. 

i  =  iutesliue.  vd  =  vas  deferens. 

u  =  single  uephridium  which  serves  also  us  the  oviduct. 

The  last-named  genus  is  interesting  as  affording  an  exam- 
ple of  sexual  dimorphism,  the  males  being  small  Turbellarian- 
like  organisms  which  live  parasitically  in  tlie  anterior  portion 
of  the  digestive  tract  of  the  female,  only  coming  to  the  exterior 
lor  the  purpose  of  copulation. 

2.  Order  Sipunculacea. 

The  Sipunculacea,  to  which  the  term  Gephyrea  inermes  is 
also  applied,  is  an  order  including  forms  which  lack  all  traces 


342 


mVERI'EBRATE  MOBPHOLOGT. 


Mi 


r 


of  setae.  In  Priapidus  the  iutestiue  is  almost  straight  and  the 
iinus  terminal ;  but  in  Sipunculus  and  the  allied  genera,  such  as 
FJiascolosoma  and  PhascoUon,  the  digestive  tract  is  convoluted 
and  bent  back  upon  itself,  so  that  the  anus  lies  on  the  dorsal 
surface  near  the  anterior  extremity  of  the  body.  A  "  respira- 
tory tree  "  is  absent  or  rudimentary  as  a  rule  except  in  Pria- 
pulus  and  allied  genera,  and  the  large  prostomial  lobe  char- 
acteristic of  the  EchiureoB  is  lacking.  The  anterior  por- 
tion of  the  body,  however,  is  capable  of  being  invaginated  by 
means  of  strong  retractor  muscles  (Fig.  109,  dR  and  vR)  into 
the  fore  part  of  the  digestive  tract,  forming  the  so-called  in- 
trovert. The  extremity  of  this  is  provided  with  a  circle  of 
finger-like  or  branched  tentacles  in  the  centre  of  which  lies 
the  mouth,  and  which  are  supposed  to  have  a  respiratory 
function,  being  riohly  supplied  with  blood.  In  Priapulus 
these  are  absent,  but  at  the  posterior  end  of  the  body  there 
is  a  prolongation  which  bears  papilla-like  processes  which 
probably  fur.ction  as  respiratory  organs. 

Development  and  Affinities  of  the  Gephyrea.~T]:e  early  development 
•of  the  Gephyrea  resembles  closely  that  of  the  Polyeh-jeta,  more  especially  in 
the  Echiureae.  In  this  ordera  Troehophore  larva  is  formed  resembling  very 
closely  the  typical  Polygordius  troehophore,  the  similarity  extending  even 
to  a  segmentation  of  the  primitis^e  mesoderm  bands.  In  later  stages  this 
metamerism  of  the  mesoderm  disappears,  no  trace -uf  it  being  found  in  the 
adult  forms.  In  the  Sipunmlacea  the  larva  differs  from  tiio  Troehophore 
in  lacking  the  typical  praeoral  band  of  cilia,  thougli  this  may  t  ^  weakly 
■developed  in  some  forms,  such  as  Phaseolosoma.  The  postoral  cilia  are,  on 
the  other  hand,  strong.  A  further  dilTerence  is  found  in  the  absence  of 
metamerization  of  the  mesoderm,  which  at  a  very  early  st.ige  of  develop- 
ment forms  a  layer  lining  the  interior  surface  of  the  body- wall,  and  also 
covering  the  digestive  tract  and  enclosing  a  cojlomic  cavity  continuous 
through  the  entire  body. 

Notwithstanding  these  important  differences  thore  seems  little  room  for 
•doubt  but  that  the  Sipimculus  larva  has  arisen  as  an  aciptation  of  the 
typical  Annelidan  Troehophore  still  represented  in  the  development  of  the 
Echiurese.  By  these  forms  a  clone  relationship  is  shown  to  the  Polychrota  ; 
and  the  Gephyrea  are  to  be  regarded  as  Polychaeta  which  have  secondarily 
lost  a  metamerization  originally  present  in  the  adult  ancestors  and  still 
represented  in  the  Echiurus  larva,  but  lost  even  in  the  larval  stages  (»f  the 
Sipunculacea. 

Since  the  discovery  of  the  larval  forms  of  certain  Echiurid  and  Sipuu- 
<5Ulid  forms  there  has  been  a  tendency  to  regard  these  two  orders  as  being 


TYPE  ANNELIDA. 


24^S 


laucb  less  closely  related  than  thoy  are  here  supposed  to  be.  The  Echiure® 
are  stiU  held  to  have  Anuolidan  affinities,  while  the  Sipunculacea  are  as- 
signed to  the  next  type  to  be  described.  This  tendency  has  its  origin  in 
the  attachment  of  too  great  importance  to  the  metamerism  which  i&  indi- 
cated in  the  Echiurid  trochophore  but  lacking  m  the  Sipunculid  larva 
Ihere  seems  no  good  ground  for  suppohxng  that;  its  absence  in  the  latter 
group  may  not  be  sufficiently  explained  by  the  assumption  that  it  repre- 
sents the  final  stage  of  the  reduction  of  metamerism  ,f  which  the  transient 
segmentation  of  the  Echiurid  is  a  stage.  In  their  anatomical  character- 
istics the  adult  forms  of  the  two  groups  are  tea  much  alike  to  be  assigned 
to  different  types  and  the  similarities  of  deiail  too  numerous  to  warrant  the 
belief  that  they  have  been  independently  acquired.  It  seems  much  more 
probable  that  both  orders  liave  descendod  from  segmented  aucestors—the 
degeneration,  if  degeneration  it  can  be  called,  having  been  carried  to  a 
greater  extent  in  the  Sipunculacea  than  in  the  Echiureee,  and  having  in 
consequence  been  thrown  back  upon  the  laival  stages  and  so  obscuring  the 
developmental  evidences  of  the  phylogeny. 

A  connecting  link  between  the  Echiureqe  and  the  Polychseta  has  been 
traced  by  some  authors  in  the  genus  Sternaspis,  atone  time  associated  with 
the  Gephyrea  but  now  universally  assigned  to  the  Polychsta.  In  this 
genus  the  metamerization,  though  to  a  certain  extent  reduced,  is  still  pro- 
nounced, S.  arcuata  consisting  of  from  twenty  to  twenty-two  metameres. 
of  which  the  anterior  seven,  together  with  the  head-lobes,  may  be  invagi'- 
nated— the  introvert  of  the  Sipunculacea  being  thus  recalled.  On  the  ven- 
tral surface  near  the  posterior  extremity  of  the  body  are  two  shield -like 
plates  armed  with  setae,  and  at  the  posterior  exlremity,  as  in  PnapiiUts, 
are  a  number  of  filamentous  appendages  which  are  regarded  as  brancliite. 
Setae  are  present  on  all  the  metameres  except  the  fifth,  sixth,  and  seventh  • 
those  of  the  eighth  to  the  sixteenth  metameres  being,  however,  concealed 
beneath  tne  hypodermis.  The  digestive  tract  is  somewhat  convoluted,  but 
opens  terminally  ;  the  ventral  nerve-cord  shows  traces  of  ganglionic  swell- 
ings, and  at  the  posterior  end  of  the  body  possesses  a  marked  enlargement ; 
and  only  two  nephridia  are  present.  The  musculature  and  the  vascular 
system  resemble  those  of  the  Polychaeta  rather  than  those  of  the  Gephyrea, 
while  the  reproductive  organs  are  peculiar  in  possessing  special  ducts, 
which,  it  has  been  held,  show  no  indications  of  being  modified  nephridia. 

In  many  respects,  accordingly,  Sternaspis  does  hold  a  position  interme- 
diate between  the  Echiure*  and  the  PolychaBta,  and  it  seems  not  improb- 
able that  it  may  represent  an  offshoot  from  near  the  base  of  the  line  along 
which  the  Gephyrea  have  been  differentiated.  Whether  this  be  the  case  or 
not,  it  is  exceedingly  probable  that  the  Gephyrea  have  been  derived  from 
tiie  Polychaeta,  the  Echiurea*  preserving  more  numerous  traces  of  their  an- 
cestry than  do  the  Sipunculacoae. 


244 


INVERTEBRATE  MORPHOLOGY. 


IV.  Class  Myzostomeae. 

The  MyzostomesB  constitute  a  group  of  Annelids  which  pre- 
sent but  few  traces  of  a  typical  metameric  form,  being  much 
modified  by  their  parasitic  habit.     All  the  known  forms  are 
parasitic  upon  Crinoids,  some  producing  malformations  of  the 
pinnules  of  their  host  in  the  form  of  cysts  in  the  interior  of 
which   they  live.      The   body   of   Myzostomum  (Fig.  Ill)   is 
flattened  and  oval,  a  number  of  finger-like  processes  or  cirri 
(c)  projecting  around  the  margin.    There  is  no  trace  of  external 
segmentation,  although  five  pairs  of  parapodia  ( /)),  each  with 
an  axial  supporting  chitinous  rod  and  a  single  hooked  seta, 
occur  on  the  ventral  surface.      On  the  same  surface  too,  near 
the  margin,  are  to  be  found  in  most  species  three  or  four 
sucker-like  depressions  {su)  on  each  side,  which  have  been 
supposed  to  represent  highly-modified  nephridia. 

The  body  is  covered  by  a  thick  cuticle  beneath  which  lie 
the  hypodermis  and  the  musculature  of  the  body-wall,  which 
has  the  characteristic  Auuelidan  arrangement.  A  body-cavity 
can  hardly  be  said  to  exist  (unless  it  be  indicated  by  the  space 
occupied  by  the  ova),  the  interior  of  the  body  being  completely 
filled  up  by  the  internal  organs  and  by  numerous  muscle- 
bands  passing  both  dorso-ventrally  and  from  side  to  side, 
these  latter  in  some  forms  being  arranged  in  such  a  way  as 
to  represent  incomplete  dissepiments.  There  is  no  blood 
vascular  system. 

The  mouth  is  situated  near  the  anterior  end  of  the  body  on 
the  ventral  surface  and  opens  into  the  proboscis-sheath, 
within  which  lies  the  proboscis  {ph),  constructed  upon  the 
same  plan  as  that  of  the  llhynchobdellid  Hirudinea.  Around 
the  extremity  of  the  proboscis  are  arranged  a  number  of 
short  tentacles,  and  its  walls  are  very  muscular;  behind  it 
opens  through  a  short  oesophagus  into  the  wide  intestine  (s) 
from  which  three  (or  two)  branched  pouches  project  on  either 
side  towards  the  margin  of  the  body.  The  short  and  relatively 
narrow  rectum  (r)  opens  near  the  posterior  end  of  the  body, 
uniting  shortly  before  its  termination  with  the  oviduct. 

The  nervous  system  consists  of  a  circumoesophageal  com- 
missural ring  upon  which  lie  numerous  scattered  ganglion-cells 


TYPE  ANNELIDA. 


246 


likewise  surrounding  the  oesophagus  and  apparently  represent- 
ing the  supraoesophageal  ganglion.  Numerous  longitudinal 
nerves  pass  forward  from  the  ring  to  unite  with  another  ring 
around  the  base  of  the  proboscis  from  which  nerves  pass  to 
the  tentacles.  Below  the  intestine  lies  a  large  ganglionic  mass 
with  which  the  circumoesophageal  commissures  unite  and 
which  gives  off  a  number  of  peripheral  nerves.     This  mass  is 


mo 


Fig.  111. — Myzostomum  (after  von  Graff) 
c  =  cirrus. 
do  =  cloacal  opening. 
fo  =  opening  of  uterus  into  cloaca. 
0  =  opening  of  male  reproductive  organs 
p  =  parapodium. 

ph  =  proboscis. 


r  =  rectum. 

s  =  stomach. 
8U  =  sucker. 

t  =  testes. 
u  =  uterus. 


composed  of  several  (probably  6)  united  ganglia  and  represents 
the  ventral  nerve-cord  of  other  Annelids.  Nerves  pass  pre- 
sumably from  the  supracesophageal  ganglion-cells  along  the 
dorsal  wall  of  the  intestine  and  seem  to  constitute  a  sympa- 
thetic system.  The  only  structures  which  can  be  considered 
sense-organs  are  the  marginal  cirri  and  the  tentacles  of  the 
proboscis,  which  probably  have  a  tactile  function.  No  traces 
of  eyes  have  yet  been  observed. 

Nephridia,  unless  they  be  represented  by  the  snclcer  Hire 
depressions  and  the  oviducts,  are  wanting.    The  Myzostomese 


1 


24« 


INVERTEBRATE  MORPIIOLOOY. 


are  as  a  rule  lierraaphrodite.  It  seems  doubtful  if  the  ovaries 
have  actually  been  made  out,  the  large  masses  of  ova  {ov) 
lyiug  between  the  branches  of  the  intestinal  pouches,  which 
have  been  considered  ovaries,  being  more  probably  original 
ccelomic  spaces  which  have  become  filled  with  ova  set  free 
from^  the  ovaries;  while  the  so-called  uterus  (?<),  lying  im- 
mediately above  the  intestine,  and  which  in  mature  animals 
is  closely  packed  with  ova,  is  probably  of  the  same  nature. 
Three  oviducts,  one  dorsal  and  two  lateral,  pass  from  the  uterus 
to  open  ifo)  into  the  rectum  near  its  termination,  though  the 
dorsal  one  in  some  forms  may  open  directly  to  the  exterior 
near  the  anus. 


If  the  uterus  is  correctly  ident'fied  as  a  ccelomic  space,  then  it  seems 
not  improbable  that  the  oviducts  may  represent  modified  nephridia. 
Their  opening  into  the  rectum  is  a  secondary  condition  and  does  not 
necessarily  stand  in  opposition  to  their  nephridial  character,  since  practi- 
cally the  same  conditions  obtain  in  some  Rotifera. 

The  testes  {t)  are  branched  organs  lying  for  the  most  part 
between  the  intestine  and  the  nervous  system,  though  isolated 
masses  occur  in  some  forms  near  the  margin  of  the  body.  On 
each  side  two  vasa  deferentia,  one  anterior  and  one  posterior, 
convey  the  spermatozoa  to  a  muscular  sperm-vesicle  opening 
to  the  exterior  at  the  margin  nearly  opposite  the  centre  of 
the  body  (mo). 

In  some  species,  notwithstanding  their  hermaphroditism,  "  comple- 
montal  males,"  small  individuals  which  possess  ripe  spermato/oa  while 
lacking  ova,  have  been  described  as  occurring.  Fiiithcr  observations  have 
not,  however,  tended  to  conlirni  tliis  idea  in  its  original  sense,  since  these 
small  individuals  have  been  found  to  be,  like  tiie  larger  ones,  hermai)hr()- 
dites,  being  secondary  adaptations  from  the  prevailing  hermaphroditic 
condition,  and  not  Iniviug,  therefore,  the  same  significance  as  the  "com- 
plcnienlal  males"  of  the  Cirrhipedia  U{.  v). 

There  can  be  little  room  for  doubt  but  that  the  MyzostoraoiB  are  Ainielida 
degenerated  by  parasitism,  and  that  they  are  most  closely  related  to  the 
Polycl.inta.  It  is  interesting  to  note  in  this  connection  the  effect  their 
parasitic  and  sessile  mode  of  life  under  eijuable  oxteruul  conditions  has  had 
in  producing  indications  of  u  radial  symmetry. 


TYPE  ANNELIDA. 


247 


APPENDIX  TO  THE  TYPE  ANNELIDA. 
Class  PHOEONiDa;. 

The  class  PlioronidaB  iuchules  a  siugle  genus,  Phoronis,  of 
wliich  but  a  few  species  are  kuoAvu.  Tliey  are  all  marine 
forms  of  comparatively  small  size,  reaching  in  some  cases  a. 
length  of  50  mm.  Each  iudivitlual  is  contained  within  a. 
chitinous  tube  to  which  particles  of  sand  are  in  some  cases 
agglutinated,  and  is  worm-like  and  cylindrical  in  form,  the 
anterior  extremity  of  the  body  being  provided  with  a  horse- 
shoe-shaped fold,  termed  the  lophophore  (Fig.  112,  a),  bearing 
a  number  of  tentacles  arranged  around  its  margins.  Between 
the  two  circles  of  tentacles  is  sitiu.ted  the  mouth  (/>),  over 
which  hangs  a  fold  known  as  the  epistome,  representing  the 
prostomium  or  pnt'oral  lobe  of  the  larva.  Outside  the  area 
enclosed  by  the  tentacles  is  the  anus,  on  either  side  of  which 
a  i)ore,  the  opening  of  a  nephridium,  is  found. 

The  ectoderm  of  the  body-wall  is  separated  by  a  distinct 
basement-membrane  from  a  layer  of  circular  muscles,  within 
which  is  a  second  layer  of  longitudinal  muscles  (?)— an  arrauge- 
mcut  resembling  that  found  in  the  body-wall  of  the  Annelids, 
internally  the  longitudinal  muscle-layer  is  lined  by  a  layer 
of  peritoneal  cells  enclosing  a  spacious  ccelom.  Near  the- 
anterior  end  of  the  body  there  is  a  transverse  septum  sepa- 
rating off,  more  or  less  perfectly,  an  anterior  chamber,  with 
which  the  cavity  of  the  epistome  and  of  the  lophophore  com- 
nninicates,  from  a  larger  posterior  chamber  in  which  lie  the 
intestine  and  reproductive  organs,  and  which  is  divided  lon- 
gitudinally by  three  mesenteries  extending  from  the  intestine 
to  the  body-wall.  One  of  these  mesenteries  accompanies  the. 
intestine  throughout  its  entire  extent,  while  the  other  two. 
lateral  mesenteries  are  in  connection  only  with  the  sides  of 
the  descending  limb  of  the  intestine. 

The  tentacles  are  processes  of  the  body-wall,  with  a 
ciliatotl  ectoderm,  and  contain  a  chitinous  axial  supporting 
tissue, 

A  completely  closed  blood  vascular  system  is  present, 
coiiHisting  below  the  transverse  septum  oif  two  longitudinal 


246 


INVERTEBRATE  MORPHOLOGY. 


vessels  {li  aud  /).  One  of  these  (/)  divides  {g)  near  the  an- 
terior extremity  of  the  body,  the  two  branches  passing  into  a 
circular  vessel  lying  at  the  bases  of  the  tentacles  and  sending 

branches  up  into  them.  The 
vessels  Avhich  return  the 
blood  from  the  tentacles  open 
into  a  second  ring  external 
to  the  first,  aud  from  it  two 
vessels  pass  ^-ick wards  and 
unite  to  form  the  second 
longitudinal  trunk  from  which 
numerous  cjccal  pouches 
arise.  All  the  vessels  have 
contractile  walls,  aud  the 
blood  which  they  contain 
possesses  nucleated  red  cor- 
puscles. 

The  digestive  tract  is  bent 
Fig.    113.— Lateral   view   of    An-   upon    itself    (t^    and    e),   tli.' 
TEHiou   Keoion  of  r/iorouis  (after  mouth  and  anus,  as  already 

described,  lying  in  close  prox- 


imity at  the  anterior  extrem- 
ity of  the  bod}'.  Several 
regions,  such  as  a;80])hagus, 
first  stomach,  second  stoni- 
acli,  aud  intestine,  are  to  Ik; 
distinguished,  aud  along  one 


Bol'RNK). 

a  =  lophophore. 

b  —  inoiitli,  surrounded  by  epistome 

e  =  lophophoral  disk. 

d  =  OBHOpluigUS. 

f  =  intestine. 

/  =  ventral  bloodvessel. 

g  =  brimcb  of/. 

h  =  dorsiil  blood-vessel. 

i  =  Ioiif?itu(iiniil  inuscli!  of  body-wnll.    surface  of  the  oesophagus  and 

k  =  interlentiicular  membrane.  fl^.^^      stomach     ruus      in      I\ 

architecfa  a  ridge,  becoming  a  groove  in  the  stomach  region, 
of  ciliated  gland-cells,  which  recalls  the  accessory  iutestiue 
of  the  Gephyrea.     There  are  no  special  digestive  glands. 

The  nervous  system  is  com])letely  imbedded  in  the  ecto- 
derm. It  consists  of  a  nerve-ring,  following  the  outline  of 
the  lophophore  at  the  bases  of  the  tentacles  and  surround- 
iug,  therefore,  the  mouth  but  not  the  anus.  From  it  a  nor\t' 
ruus  backward  asymmetiicidly  upon  one  side  of  the  body 
to  near  the  posterior  extremity.  It  contains  a  largo  clear 
rod-like  structure  which  seems  to  be  a  colossal  nerve  fibif. 


TYPE  ANNELIDA. 


249 


The  only  sense-orgaus  which  have  beeu  described  are  a  pair 
of  ciliated  depressious  lyiug  one  on  each  side  in  the  concavity 
of  the  lophophore  ;  no  definite  statement  can  be  made  as  to 
their  function. 

A  single  pair  of  nephridia  is  present,  opening  into  the 
posterior  chamber  of  the  coelom  by  fuuuel-like  mouths,  and  to 
the  exterior  on  each  side  of  the  anus.  They  serve  not  only 
for  excretion,  but  also  as  ducts  for  the  reproductive  elements. 
The  various  species  of  Phoronis,  \yith  the  possible  exception 
of  P.  arcMteda,  are  hermaphrodite,  the  ova  and  spermatozoa 
developing  from  cells  of  the  peritoneum  lyiug  in  the  vicinity 
of  the  pouched  longitudinal  blood-vessel.  They  are  shed 
from  their  place  of  formation  into  the  coelomic  cavity  and 
thence  pass  to  the  exterior  through  the  nephridia. 


Frd.  118.— Metamoki'Iiosih  of  Actinotrochn  (after  MitTsrHNiKOFF  from  BALrot'R). 

in  =  invMiiiiiMfion. 

Development  of  the  Phownida-.—Iu  their  deve'opmeut  the 
various  species  of  Phoronis  ho  far  as  kuowu  undergo  a  very 
r.'inarlaible  metamorphosis.  Tlie  larva  which  develops  from 
the  ovum  is  knowji  as  Actinotrochn  (Fig.  113,  ^)aud  is  a  some, 
what  eloijgated  Htructure  possessiug  at  the  anterior  end  a 
large   hood  which  overhangs   the  mouth,   its  edge   bearing 


250 


IN  VERTEBRA  TE  MOEPHOLOG  T. 


strong   cilia.     Beliiud  the  mouth   are  a  number  of  ciliated 
tentacle-like    processes    arranged    in    a    horseshoe-shaped 
curve,  their  cilia,  together  with   those   of  the   edge  of  the 
prostomial  hood,  f(5rmiug  a  baud  encircling  the  mouth.     The 
digestive  tract  opens   to   the   exterior  at  the   posterior  ex- 
tremity of  the  body,  and  the  axis  of  the  body  is  the  axi» 
passing  through  the  anus   and  the  centre  of  the  prostomial 
lobe.     A  little  later  {Ji)  an  invagination  (in)  of  the  body-wall 
into  the  coelora  of  the  larva  develops  on  the  ventral  surface 
behind  the  band  of  ciliated  processes  and  becomes  of  a  con- 
siderable size.     At  the  time  of  the  metamorphosis  this  in- 
vagination is  suddenly  everted  (Fig.  113,  C  and  D),  the  intes- 
tine being  carried  with  it  as  a  loop,  and  entirely  new  axial 
relations  are  thus  brought  about.     The  long  axis  of  the  body 
is  now  (D)  almost  at  right  angles  to   what  it   was  in   the 
Acthiotrocha,  and  since    the   invagination   originally  formed 
on  the  ventral  surface  of  the  larva,  the  body  of  the  adult 
l-horonis  must  be  regarded   as  formed   by  an  excessive  de- 
velopment of  the  veutral  surface,  the  dorsal   surface  beiug 
represented  only  by  the  short  interval  between  the  mouth,  or 
ratlier  the  epistome,  and  the  anus.     The  epistome  rei)resents 
the  prostomial  lobe  of  the  larva,  and  the  ciliated  processes 
represent  the  lophophoric  region,  though  they  themselves  are 
afterwards  replaced  by  the  permanent  tentacles. 

There  can  of  course  be  no  question  but  tliat  this  remarkable  metamor- 
phosis is  a  .secondary  plienomonon,  and  it  .seems  probable  that  its  acquisi- 
tion stands  in  relation  to  the  tubicolous  habits  of  the  adult  which  nocos- 
.sitato  the  change  of  the  principal  axis  of  the  body.  The  metamorphosis  is 
the  means  of  avoiding  a  slow  and  tedious  change  necessitated  by  tlie  'lifler- 
ent  habits  of  the  larva  and  the  aduU,  just  as  the  occurrence  of  the  ehry- 
snlis  stage  in  the  development  of  the  butterfly  is  required  on  account  of 
the  great  differences  between  the  mouth-parts  of  the  larval  caterpillar  and 
the  aduli  biittcrliy. 

The  affinities  of  Phoronis  cannot  bo  considered  to  be  finally  settled  as 
yet,  though  there  has  been  a  tendency  of  late  years  to  associate  them  with 
the  Polyzoa.  They  also  seem  to  show  affinities  to  the  Gephj-roa,  and  hy 
Korae  authors  are  considered  more  correctly  referable  to  that  group.  The 
r.ndency  to  develop  the  ventral  surface  of  the  body  at  the  expense  of  ilic 
dorsal  and  so  to  form  a  new  body-axis  is  seen  in  Sipnmmlus  and  carritd 
t;;  its  eriijri:rir;iiuii  in  Phurnnis,  and  furtiicr  ,>iinilaiilit's  iwiweeu  tiio  two 
forms  lire  t(»  he  found  in  the  character  of  the  nephridia  and  in  the  occur- 


TYPE  ANNELIDA. 


251 


rence  of  a  closed  blood  vascular  system.  The  lophopliore  of  Phoronis,  and 
tlie  epistome,  are  on  the  other  hand  characteristic  Polyzoan  features,  and  it 
seems  not  at  all  improbable  that  Phoronis  occupies  an  intermediate  posi- 
tion between  the  Gephyrea  and  the  Polyzoa.  There  is  this  at  all  events  to 
be  noted  concerning  the  Prosopygia  (see  following  chapter),  and  that  is 
that  they  are  certainly  closely  related  to  the  Annelida.  If  the  supposition 
advanced  on  p.  343  to  the  effect  that  the  Sipunculacea  are  to  be  regarded 
as  Annelida  which  have  secondarily  lost  their  metamerism  be  correct,  and 
li  Phoronis  really  indicates  a  derivation  of  the  Prosopygia  from  Gephyrean- 
liko  ancestors,  then  the  Prosopygia  too  must  be  regarded  as  Annelida  in 
which  all  traces  of  metamerism  have  been  lost.  This  view  seems  preferable 
to  that  which  would  refer  the  Polyzoa,  for  instance,  back  to  unsegmented 
ancestors— back,  that  is  to  say,  to  the  non-segmented  ancestors  of  the 
Annelida. 


SUBKINGDOM  METAZOA. 
TYPE  ANNELIDA. 

I.  Class  Ch^topoda.  —  Metamerism  usually  well  marked  ;  with  dorsal 
and  ventral  rows  of  set*  along  the  sides  of  the  Ixuly. 
I.  Subclass  PoLYCHJiTA.— Marine  forms  ;  with  the  setaj  usually  borne 
upon  lateral  lobes  of  the  body  (parapodia). 
1.  Order  ^rt'/<m«)<e/j(/a.—Witliout  parapodia.    Pohjgordhis. 
3.  Order  i'/VY//<^/«.— Elongated  swimming  or  creeping  forms; 
nietanieres   more  or    less  similar.     Nereis,  Lepichnotns, 
Diopatra,  Autuli/tus,  Hesione,  Syllis,  Alciope,  Capitella, 
P)ll/(>/)fUhalmus,  Arenicola,  Aricia. 
3.  Order  ^edentaria. —VsunWy  tubicolous  ;  anterior  metanieres 
more  or  less  different  from  the  rest.  Amphitrite,  USerptila, 
Sahel'a,  Terebella. 
II.  Subcla.ss  OLKiocH.CTA.— Aquatic  or  terrestrial  forms;  with  setas 
but  without  parapodia. 

1.  Order  Naidomorpha. —¥ov  the  most    part    aquatic;   fre- 

quently reproflucing  nousexually ;  nephridia  servo  as  re- 
productive ducts.  Nais,  Dero,  C/i(etobrunchii.s;  uEolc- 
sonia,  Ch(vt(uinster,  Cfenodrifiis,  Tubi/ex. 

2.  Order  Lnmbriiomorpha.~Y(n'  tlie  most    part   terrestrial; 

not  i'oproducing  non  sexually  ;  special  reproductive  dtiets. 
LuiiihriruSy  Perich(tta,  Aikh    'fa. 
II.  Class  IIiiiUDlNEA.— Metinnerism   \x(>]\   marked  ;    without  setip  ;    with 

anteiior  and  posterior  suckers. 
1.  Order  6' m///*(*/*f/('//«(/(r.— Mouth  with  three  more  or  less  well 
developed  teetii ;  pharyn.x  not  protrusible.    Ilirudo,  Ma- 
crobdtlla,  Nep/ieli.s. 


252 


IN  VERTEBRA  TE  MOIiPHOLOG  T. 


2.  Order  RhynelwhdeUidcB.—W ifhont  teeth  and  with  protnislble 

pharynx.     Clepsine,  Povtobdella,  Piscicola,  Branchellion. 

III.  Class  Gephyrea.— Metamerism  indistinct ;  without  parapodia. 

1.  Order  Ec1dure<je.—\N ith.  setae.     Echiurus,  Thalassema,  Bo- 
nellia. 

3.  Order  Siptinmlacece.—Vi ithowi  setae.    Sipuneiilus,  Piiapu- 

lus,  Phascolosovm,  Phascolion. 

IV.  Class  Myzostome^.— Parasitic  on  Crinoids ;  approximating  a  radial 

symmetry.    Myzostoma. 


APPENDIX. 


Class  Phoponid^.— Without  metamerism  ;   tubicolous  ;    with  lophophore. 
Phoronis. 


LITERATURE. 

Cir^TOl'ODA. 

A.   de  Qiiitrefages.     Ilistoire  naturelle  des,  Amides  marina  et  d'eau  douce. 

Paris,  18«5. 
E.  Ehlers.     Die  Borstemciirmer.     Leipzig,  1864-68. 
E.  Meyer.     Studien  iiher  den  Korperbau  der  Annelideii.    Mitth.  a.  d.  zoiAog. 

Station  zu  Neapel,  vii,  1887 ;  viir,  1888. 
H.  Eisig.     Die  Qipitellideii  des  Golfes  von  Neapel.     Fauna  und  Flora  des  Golfes 

%'on  Neapel.     Monogr.,  xvi,  1887. 
J.  Fraipont.     Le  genre  Polygordius.     Fauna  und  Flora  des  Golfes  von  Neapel. 

Monogr.,  xvi,  1887. 

E.  Claparede.     Jleehevfhes  aiudomiqnes  sur  ces  Oligochetes.     Geneve,  1862. 

F.  Vejdovsky.     Monogmphie  der  Enchytradden.     Prag,  1879. 
System  vnd  Morphologie  der  Oligocha'ten      Prag,  1884. 

0.  E.  Beddard.     A  Monogr" ph  of  the  Order  of  Oligochcela.     Oxford,  1895. 

Numerous  papers  on  Oligochieta  by  G.  E.  Beddard  and  W.  B.  Benbam  in 
Quarterly  Journ.  Microscop.  Science. 

IIIHUDINEA. 

A.  Moquin-Tandon.     Moiiographie  de  lafamille  de  Iliriidinees.     Paris,  1846. 
C   O.Whitman.    The  Leeches  of  JajMn.  Quarterly  Journ.  of  Microscop.  Science, 

.xxvr,  1886, 

Tite  Metdmenam  of  Clepsine.     Festschr.  zuna  siebenzigsten  Geburtstntre 

Hiidolf  litMickarts.     lieipzig.  1893. 
A.  0.  Bourne.     Contrihufions  to  th(    Aiuitniny  of  the  Hirudinea.     Quarterly 

Jouru.  of  Microscop.  Science,  xxiv,  1881. 

OKIMIYHEA. 

R.  Oreef.     Die  Echiitreu  (Gephyrxi  itrvmia).    Nova  Acta  Leopol.  Carol.  Akail., 

xi.i,  1879. 
E.  Selenka.     J)ie  Slpinieuftden.     Wicsbaii*  n,  1883. 
E.A.Andrews.     Xntis  mi    the    .\ii(ili>>iiy  cf    -'iiinculiis   Gotildii,   Pourtolts. 

Studies  from  the  Hiolog.  l-iilior.  Johns  Hopkins  Univ.,  IV,  1890. 


TYPE  ANNELIDA. 


^m 


MVZOSTOMIDA. 

L.  von  Graff.     Das  Genus  Myzostoma.     Leipzig,  1877. 

Report  on  tlie  Myzostomidm.     Scient.  Results  of  the  Voyage  of  H.M.S. 

Challenger.     Zool,  x,  1884. 
J.  Beard.     On  the  'Life-history  and  Development  of  the  Genus  Myzostoma. 

Mittb.  a.  d.  zool.  Station  Neapel,  v,  1884. 
W.  M.  Wheeler.     Tlie  Sexual  Phases  of  Myzostoma,     Mittb.  aus  der  zoolog. 

Station  zu  Neapel,  xii.  1896. 

PHORONIDA. 

E.  B.  ■Wilson.    The  Origin  and  Significance  of  the  Metamorphosis  of  Actinotroeha. 

Quarterly  Journ.  Microscop.  Science,  XXi,  1881. 
C.  J.  Cori.     Untersuchungen   iiber  die  Anatomic  und  Histologie  der  Oattung 

Phorohis.    Zeitscbr.  fUr  wissenscb.  Zoologie,  Li,  1891. 


s 


254 


INVEliTEBEATE  MOliPHOLOO  Y. 


s/ 


CHAPTER  XI. 


TYPE  PROSOPYGIA. 


The  members  of  the  type  Prosopygia  are  compact,  soli- 
tary,  or  coloiiial  orj^auisms  destitute  of  a  true  metamerism 
iiud  liaviug  the  digestive  tract  usually  bent  upon  itself,  so 
that  the  auus  lies  iu  more  or  less  close  proximity  to  the 
mouth  and  therefore  uear  the  anterior  end  of  the  body.  A 
<3hitinous  or  more  or  less  calcareous  investment  is  formed 
•about  the  exterior  of  the  body,  and  in  some  cases  assumes 
the  form  of  a  calcareous  bivalve  shell,  similar  to  that  of  the 
Pelecypoda  in  its  general  appearance,  although  in  the  rela- 
tions of  the  valves  to  the  body-surfaces  and  in  other  particu- 
lars (see  p.  327)  there  are  very  decided  differences,  the  simi- 
larity being  simply  an  analogy. 

A  more  characteristic  feature,  however,  is  the  presence  at 
•the  anterior  end  of  the  body  of  a  circular  or  horseshoe-shaped 
fold,  or  else  of  two  armlike  lateral  processes,  forming  what 
is  termed  the  lophophore,  upon  which  are  borne  a  number  of 
tentacles  which  play  important  roles  not  only  iu  obtaining 
food,  but  also  iu  the  process  of  resj^iration,  no  branchial  or 
other  special  respiratory  organs  being  present. 

A  more  or  less  spacious  coelom  is  usually  present,  trav- 
ersed by  muscle-fibres  and  some  specially  developed  muscle- 
bands,  though  the  must  lar  system  is  on  the  Avliole  poorly 
developed.  The  coelom  contains  a  Incmolymph,  but  a  sepa- 
rate blood  vascular  system  and  heart  is  entirely  wanting. 
The  nervous  system,  in  accordance  witli  the  absence  of  met- 
amerism, is  exceedingly  simple,  consisting  either  of  a  single 
ganglion,  lying  between  the  mouth  and  anus  and  sending  off 
nerves  to  the  various  regions  of  the  body,  or  else  of  a  nerve- 
ring  surrounding  the  oesophagus,  with  more  or  less  distinct 
supra- and  sub-cjesophageal  ganglionic  enlargements.  Special 
sense-organs  are  wanting. 


TYPE  PliOSOPTGJA. 


255 


A  pair  of  simply-constructed  nephridia  are  present  in 
some  forms,  but  in  many  a  special  excretory  organ  seems  to 
be  entirely  wanting.  Bisexuality  is  the  usual  arrangement, 
although  in  the  Polyzoa  hermaphroditism  is  of  not  unfre- 
quent  occurrence. 

The  great  majority  of  the  Prosopygia  are  marine  in  habi- 
tat, though  a  number  of  Polyzoa  are  inhabitants  of  fresh 
water.  The  type  may  be  divided  into  two  well-marked 
classes,  the  Polyzoa  and  the  Brachiopoda. 


cinl 


I.  Class  Polyzoa. 

The  Polyzoa,  a  group  usually  spoken  of  by  German  zool- 
ogists as  the  Bryozoa,  are  almost  without  exception  colonial 
organisms,  forming  encrusting,  massive,  or  more  or  less  den- 
dritic masses  composed  of  a  large  number  of  small  individuals 
or  polypides,  each  of  which  is  enclosed  within  a  chitinous  or 
in  some  cases  partially  calcified  investment,  the  zooecium,  from 
the  mouth  of  which  the  anterior  portion  of  the  body  bearing 
the  lophophore  may  be  protruded.  This  outer  investment  or 
edoci/st  (Figs.  115  and  116,  ec)  is  lined  upon  its  interior  sur- 
face by  a  layer  of  ectoderm-cells,  within  which  is  a  delicate 
peritoneal  lining,  these  two  layers  together  constituting  the 
true  body-wall  or  endocyst  (Fig.  115,  en)  practically  destitute 
of  muscle-tissue,  though  a  sphincter  is  usually  present  at 
the  mouth  of  the  cup,  which  may  thus  be  closed  over  the  re- 
tracted polypide. 

A  more  or  less  spacious  coelom  (Fig.  115,  co)  is  present  in 
the  majority  of  forms,  containing  a  lucmolymph  and  tra- 
versed  by  a  number  of  muscle-strauds  (m)  which  may  be 
aggregated  into  special  retractor  bands ;  but  in  one  order,  the 
Eiidoprocta  (Fig.  114),  these  are  wanting  and  indeed  the 
ccelom  is  reduced  to  a  very  small  space  between  the  body, 
wall  and  the  digestive  tract.  This  latter  structure  has  tlie 
characteristic  U-  or  Y-shaped  form  and  presents  but  little 
difterentiation  into  special  parts,  though  an  oesophagus, 
stomach,  lined  with  glandular  so-called  liver-cells,  and  rectum 
may  be  distingni.slied.  An  anus  (Fit^s.  115  and  116  a)  is 
iilways  present  and  may  be  situated  either  within  or  without 


256 


IN  VERTEBRA  TE  MORPIIOLOG  T. 


:f 


the  area  enclosed  by  the  lophophore.  The  nervous  system 
is  exceedingly  simple,  cousistiug  of  a  siugle  gangliouii  mass 
(Figs.  lU  and  115,  ce)  lying  between  the  mouth  and  auus» 
nerves  lamit'ying  from  it  to  the  various  parts  of  the  body. 
The  only  sen.se-organs  that  have  been  detected  are  situated 
upon  the  free  portions  of  the  bod;  more  especially  on  the 
lophophoral  tentacles  {t),  and  are  represented  by  scattered 
ectodermal  cells  each  of  which  bears  a  strong  cilium  and  is 
in  connection  with  a  nerve-fibre  ;  the}'  have  been  assigned  a 
tactile  function,  thoi  gh  ic  seems  probable  that  they  react  to 
stimuli  of  various  kinds  and  have  a  much  more  generalized 
function. 

The  arrangement  of  the  excretory  and  reproductive  organs 
varies  considerably  in  different  forms  and  may  be  more  con- 
veniently described  in  connection  with  the  various  orders. 

1.  Order  Endoprocta. 

This  order  contains  but  a  small  number  of  forms,  which, 
with  one  exception,  Urnatella,  are  marine  in  habitat.     They 

all  possess  the  power  of  reproducing 
by  budding,  colonies  being  thus  formed, 
as  in  PediceUina,  Ascopodaria,  and  other 
genera  with  the  exception  of  LoxosomUy 
in  which  the  buds  separate  completely 
from  the  parent  at  a  relatively  early 
stage  of  their  development.  Each  in- 
dividual (Fig.  114)  is  a  cup-shajjed 
structure,  prolonged  posteriorly  into 
a  stalk  (6'^)  and  upon  the  rim  of  tlie 
cup,  which  represents  the  lophophoral 
fold,  or  slightly  below  it  on  the  inner 
Fig.  114.— Single  Indi-  *^"ii'ace,  the  tentacles  (t)  are  arranged 
viDUAL    OF   PediceUina    in  a  circle  surrounding  a  depression, 

the  vestibule,  into  which  open  both 
the  mouth  and  the  anus,  the  situation 
of  tha  latter  opening  within  the  circle 
of  tentacles  having  suggested  the  name 
given  to  the  order.  The  tentacles  can 
be   coiled   in   a  circinate    manner,   so  as   to   lie   completely 


t  .- 


(after  Nitsche). 
ce  =  ganglion. 

I  =  so-c'iiUed  liver. 

s  =  stomach. 
St  =  stalk. 

t  =  tentacles. 


r^ 


TYPE  PEOSOPYGIA. 


26T 


within  the  vestibule,  and  the  rim  of  the  cup  can  be  closed 
over  them,  owinj^  to  the  presence  in  it  of  a  circular  band  of 
muscle-fibres. 

The  entire  body  is  covered  by  a  delicate  cuticular  ectocyst 
similar  to  the  cuticle  of  the  Annelids,  below  which  is  the 
ectoiierm  containinj^  numerous  gland-cells,  as  well  as  scat- 
tered sensory  hair-bearing  cells  which,  however,  have  not  been 
found  to  exist  in  some  genera  {Ascopodaria).  Scattered  mus- 
cular fibres  occur  in  the  body-wall,  but  they  do  not  as  a  rule 
reach  an  extensive  development. 

The  coelom  is  of  very  slight  extent  and  in  Lo.rosoma  is  re- 
placed by  a  gelatinous  matrix  enclosing  branching  cells  and 
muscle-fibres  and  recalling  the  parenchyma  of  the  Turbel- 
laria.  Imbedded  in  this  parenchyma  is  the  U-shaped  diges- 
tive tract,  beginning  with  the  mouth  situated  in  the  vestibule 
and  overhung  by  a  well-marked  epistome.  The  mouth  leads 
into  a  narrow  oesophagus  lined  by  ciliated  columnar  cells, 
and  opening  below  into  a  saclike  stomach  (Fig.  114,  s) 
which  forms  the  lower  transverse  portion  of  the  U.  The 
cells  of  its  anterior  (vestibular)  wall  (?)  are  large  and  destitute 
of  cilia,  and  contain  numerous  granules,  on  which  account 
they  have  been  termed  "  liver-cells."  The  intestine  forms 
the  ascending  limb  of  the  U,  and  like  the  oesophagus  is  cili- 
ated, opening  into  the  vestibule  at  the  siimmit  of  a  well- 
marked  papilla. 

The  nerve-ganglion  lies  below  the  floor  of  the  vestibule 
between  the  epistome  and  the  anal  papilla  and  is  a  single 
tluuib-bell-shaped  structure  from  which  from  one  to  three 
nerves  arise  on  each  side,  branching  to  be  distributed  to  the 
tentacles  and  muscles  of  the  body. 

A  single  pair  of  nephridia  occurs,  opening  into  the  vesti- 
bule, and  each  is  composed  of  a  number  of  perforated  cells, 
the  lumen  being  ciliated.  It  is  doubtful  whether  a  flame-cell 
occurs  at  the  inner  extremity  as  in  the  Annelid  head-kidneys, 
Avhich  otherwise  they  resemble.  Most  of  the  Endoprocta  seem 
to  be  bisexual,  though  Pedicelliva  is  perhaps  hermaphrodite. 
The  reproductive  organs  arise  from  the  mesoderm  of  the  body- 
wall,  forming  masses  projecting  into  the  parenchym.a,  ,i.nd  are 
provided  with  special  ducts  which  either  remain  independent 


3 


S 
^ 


258 


INVERTEBRATE  MORPHOLOGY. 


of  each  other  (Pedicellina),  or  unite  together  to  form  a  single 
tube  and  open  into  the  vestibule,  between  the  epistome  and 
the  ganglion. 


2.  Order  Ectoprocta. 

The  order  Ectoprocta  includes  the  great  majority  of  forms 
Avhich  are  referable  to  the  class  Polyzoa.  They  are  without 
exception  colonial  forms  of  small  size  in  which  the  tentacles 
are  arranged  either  in  a  circle  or  in  the  form  of  a  horseshoe 
surrounding  the  mouth,  the  anus  being  invariably  situated, 
contrary  to  the  arrangement  in  the  Endoprocta,  outside  the 
limits  of  the  lophophore.  The  tentacles,  too,  when  retracted 
are  not  flexed  or  coiled  as  in  the  Emloprocta,  but  are  simply 
approximated  to  form  a  bunch,  each  tentacle  being  straight 
And  parallel  to  its  fellows. 

The    most   characteristic   peculiarity  of   the   EctojDrocta, 
hoAvever,  is  the  power  which  they  possess  of  withdrawing  or 
retracting  the  anterior  portion  of  the  body  with  its  crown  of 
tentacles  within  the  posterior  part  (Fig.  115).     This  latter 
portion  is  enclosed  in  the  ectocyst  {ec)  to  which  the  body- wall 
is  closely  adherent  and  which  forms  a  chitinous  or,  in  some 
<;ases,  more  or  less  calcareous  cell,  termed  a  zoaecium.     At  the 
mouth  of  the  cell  the  cuticle  becomes  suddenly  exceedingly 
thin,  so  that  the  anterior  portion  of  the  body  is  quite  mobile, 
and  by  means  of  special  retractor  muscles  (w)  may  be  with- 
drawn within  the  zooecium.     The  retraction  is  a  process  of  in- 
vagination,  similar  to  what  occurs  in  the  withdrawal  of  the 
pharynx  of  the  Annelida,  the  most  anterior  lophophoric  part 
of  the  retracted  portion  not,  however,  sharing  in  the  invagina- 
tion :   the  whole  process  indeed  is  similar  to  what  may  be 
obtained  when  one  finger  of  a  glove  is  caught  from  within 
somewhat  less  than  half  way  from  the  tip  and  drawn  down 
towards  the  palm  ;  half  of  the  lower  portion  will  thus  be  in- 
vaginated  within   the  other  half,  while  the  tip  of  the  finger 
remains  uninvaginated. 

The  portion  of  the  body-wall  enclosed  by  the  ectocyst  is 
thin,  its  longitudinal  muscles  being  for  the  most  part  sepa- 
rated in  the  form  of  bands  traversing  the  coelom  and  funetiou- 


FlG, 


TYPE  PROSOPYOIA. 


25£> 


iug  as  retractors,  while  the  circuhir  muscles  are  specially  de- 
veloped as  a  rule  ouly  arouud  the  mouth  of  the  cup,  which 
may  by  their  action  be  closed  over  the  retracted  tentacles. 
A  relatively  spacious  ccelom,  contaiuiug  a  colorless  corpuscu- 
lated  ha3molyraph  is  preseut,  aud  is  liued  by  flatteued  perito- 


ov 


Fig.    115.— Diagkam   op  the   Stkuctuke   of  Alcyoridium  alMdum  (after 

PH(<rHO). 

a  —  anus.  io  —  iutertciitaciil.ir  organ. 

ce  -  ganglion.  m  =  retractor  muscle. 

CO  =  (.'celoin.  ov  —  ovary 

ec  =  ectocyst.  t  =  tentacles. 

671  =  eudocyst.  (e  ■=  testis. 

neal  cells,  some  of  which  bear  tufts  of  cilia.  The  iutestiue 
has  a  characteristic  Y-shape  (Fig.  IIG),  its  posterior  portiou 
being  prolonged  backwards  to  form  a  ca^cal  pouch,  from  the 
extremity  of  which  a  band  or  plate,  the  funicvhis  (Fig.  IIG,  /'), 
containing  in  some  cases  muscular  fibre  ;^,  and  lined  by  perito- 
neal cells,  arises,  and  passes  backwards  to  be  inserted  into 
the  ectocyst  posteriorly.  The  anus  (a),  as  already  stated, 
opens  on  the  anterior  surface  of  the  body,  outside  the  limits 
of  the  lopliophore,  and  between  it  and  the  mouth  lies  the 
nerve-ganglion,  which  is  frequently  hollow  aud  sends  off 
nerves  to  the  various  portions  of  the  body 


31 


260 


IN  VERTEBRA  TE  MORPHOLOG  Y. 


U 


As  ill  the  Eiidoprocta,  a  heart  aiid  a  blood  vascular  system 
is  entirely  wautiii<^-.  S[)ecial  excretory  organs  seem  to  be 
wanting  in  the  marine  Ectoprocta,  excretion  being  performed 
apparently  by  the  ha^^molymph-corpuscles  and  <.ther  meso- 
derm-cells,  especially  those  of  the  funiculus,  as  well  as  by 
the  granular  cells  of  the  stomach  and  ca-cal  jjoucli.  In  Cris- 
tdtella,  a  fresh-water  form,  however,  a  })air  of  ciliated  canals 
opening  into  the  coolom  by  ciliated  funnels  have  been  de- 
scribeil,  and  presumably  are  excretory  in  function,  the  two 
canals  uniting  together  to  open  to  the  exterior  by  a  single 
l)ore  situated  between  the  iiiouth  and  anus.  Up  to  the  pres- 
ent, however,  these  structures  have  not  been  observed  in 
other  forms  and  api)arently  they  do  not  exist  in  the  marine 
forms. 

In  some  of  these  latter  {Alcijonvlium,  etc.),  however,  a  cili- 
ated tubular  structure,  which  communicates  at  one  end  with 
the  ccelom  and  ojjens  to  tiie  exterior  between  the  tentacles 
at  the  other,  occurs  and  has  been  termed  the  intetientucuhn' 
organ  (Fig.  115,  io).  It  suggests  a  nephridium  in  its  relations, 
but  apparently  does  not  possess  an  excretory  function,  but 
serves  as  an  exit  for  tlie  reproductive  elements  to  the  exterior. 
In  other  marine  forms  and  in  all  the  fresh-wabn-  genera  such 
special  reproductive  ducts  have  not  l)een  observed,  and  tlie 
mode  of  escape  of  the  sexual  i)roducts  in  these  forms  is  still 
unknown.  Many  of  the  Ectoprocta  are  hermaphrodite,  tlie 
ova  and  spermatozoa  (Fig.  115,  ov,  te)  arising  from  the  peri- 
toneal mesoderm,  frequently  from  that  surrounding  the 
funiculus.  Whether,  however,  liermapliroditism  is  a  charac- 
teristic of  the  order  or  not  is  a  point  as  yet  undecided. 


1.  Siil)(>r(]('r  Phiilactiihvmata. 

The  members  of  this  suborder  are  exclusively  inhabitants 
of  fresh  water  and  are  characterized  by  the  tentacles  being 
arranged  in  a  horseshoe-shaped  manner  (excejit  in  the  genus 
Fmlvn'rella,  wliere  they  form  a  circle),  and  by  the  occurrence 
of  a  well-develoi)ed  h)be  or  cplstomc  overlapping  the  mouth. 

The  colonies  assume  various  shai)es  in  difl'ennit  genera, 
being  sometimes  dendritic  and  incrusting   stones  or    other 


TYPE  PliOSOPYGIA. 


261 


bodies,  as  iu  Fredericello,  or  fonniug  compact  masses,  as  in 
Ahyonella  and  Lophopus,  or  even  being  ca])able  of  motion,  as 
in  (Jnstatella.  In  some  forms,  e.g.  Lophoptis,  the  ectocjst  pos- 
sesses a  gel-itinous  consistency,  tliough  usually  it  is  cliitinous, 
and  the  various  zooecia  are  in  free  communication  with  one 
another,  nt)t  being  separated  by  transverse  partitions. 

In  addition  to  multiplying  by  the  usual  processes  of  bud- 
ding and  by  ova,  the  Phylactohcmata  develop  upon  the 
funiculus  special  internal  buds,  termed  stafohla.sts,  which  are 
(mclosed  Avithin  dense  chitinous  capsules.  These  are  set  free 
by  the  dying  and  disintegration  of  the  parent  and,  being  pro- 
tected by  the  i-esisti'nt  capsule,  retain  their  vitality  under 
conditions,  such  as  cold  and  dryness,  that  destroy  the  adult 
individual.  They  are  evidently  a  special  provision  for  tJie 
l)erpetuation  of  the  species  developed  in  accordance  with  the 
fresh-water  liabitat,  iu  v.hich  the  organisms  are  exposed  to 
various  conditions  not  apt  to  be  met  witii  in  the  ocean  ;  it  is 
interesting  to  note  in  this  connection  the  occnrrence  of  gem- 
mules  in  the  fresh-water  sponges  which  are  stri^itly  compara- 
ble to  the  statoblasts  and  have  a  similar  siguiiicauce. 

2.   Suhordor  fii/mnolmnafn. 

The  Gymnolivnuita  are  distinguished  from  the  PliylactolK'- 
mata  by  being,  with  the  single  e.vce))tiou  of  the  genus  Pah(di- 
cclhi,  marine  in  habitat,  by  the  tentacles  being  arranged  in 
th(;  form  of  a  circle,  and  by  the  invariable  absence  of  an  epi- 
stome. 

As  in  the  Phyhictoln'mata,  the  colonies  vary  greatly  in 
form,  being  in  some  cases  encrusting,  Menthmnipora,  Llns- 
h-(i,  in  others  branching,  Scrnpocellaritf,  or  in  others  again 
massive,  Alci/oiiuiium  ;  and  furthermore  the  ectocyst  ])re- 
sents  varying  d(«grees  of  consistency,  being  frequently  chitin- 
ous, but  occasionally  somewhat  g«datinous  or  calcified  to  a 
greater  or  less  extent.  The  zod-cia  are  not  in  free  communi- 
cation with  each  other,  but  each  is  closed  below  or  posteri- 
orly by  a  transverse  cliitinous  ])late  in  which  })erforations  are 
said  to  be  present,  though  doubt  has  recently  been  thrown 
upcm  tlieir  existence  as  perforations.  In  shape,  too,  the 
2<}u?ei;i  like  the  colouies  vary  greatly,  especiuliy  so  fur  as  their 


to 


262 


IN  VERTEBRA  TE  MORPHOLOO  Y. 


av 


mouths  are  concerned,  and  it  is  possible  to  divide  the  Gymno- 
Isemata  into  three  groups  or  tribes,  based  upon  these  differ- 
ences.  In  the  tribe  Oydostomata  the  zooeeia  are  usually 
cylindrical,  and  the  mouth  is  circular  and  destitute  of  any 
appendages  ;  in  the  Ctenodomata  the  mouth  is  closed  during 
retraction  by  a  series  of  bristles  which  surround  it  {Alcyonid- 
ium);  Avhile  in  the  ChUostomata,  in  which  the  ectocyst  is. 
usually  lirm  and  frequently  calcified,  the  mouth  is  closed  by  a 

lid,  the  ojoc/'cm/mw,  furnished  with  spe- 
cial muscles  {Hugula,  J/emhranipora). 
In  this  last-named  tribe  a  poly- 
morphism of  the  individuals  conipos- 
..  avi^n  ^  colony  is  frequently  found. 
Scattered  among  the  ordinarj'  indi- 
rm  viduals  others,  the  Avicularia  (Fig. 
116,  av),  may  be  found  having  fhe 
appearance  of  a  bird's  head,  the 
lower  beak  being  fastened  to  the  head 
by  a  hinge  and  having  inserted  into 
it  strong  muscles  ;  bunches  of  sensory 
hairs  are  also  ])resent,  and  when  these 
are  stimulated  the  lower  beak  is 
ra})idly  snapped  against  the  upper 
and  the  stimulating  organism  thus 
caught.  There  can  be  little  doubt 
but  that  these  Avicularia  are  specially 
modified  individuals  whose  head  and 
ujjper  beak  represent  tiie  ordinary 
iiidividnai,  while  the  lower  beak  may 
])i>ssibly  be  the  equivalent  of  the 
operculum  ;  physiologically  they  liavc 
beeu  usually  regarded  as  specializ;<>d 
for  the  purj)()He  of  catching  food  for 
the  ordinary  individuals,  but  it  is  not 
improbable  that  their  services  may 
rather  be  of  a  cleansing  nature,  re- 
moving from  the  colony  particles  of 
dirt  Hiid  the  extirota,  which  l)v  accumulating  might  interferr' 
with  the  proper  function  of  the  tentacles.     Another  polymor. 


00 


_bb 


Fin.    118.  — PouTioN    OF 
Colony  of  Hugula. 

a  =  uinis. 
av  =  ftviculiida. 
bb  =  brown  body. 
ee  =  ectofysl. 

/  --  funiculus. 
oe  =  ovici'll. 
rf»  =  reUa(!lor  muscle. 

t  =  tentacles. 


TYPE  PROSOPYQIA. 


263 


phic  form  is  known  as  the  Vihracula,  and  consists  of  a  slender 
filament  movably  articulated  to  a  rounded  structure  corre- 
spondiug  to  the  head  of  the  Avicularia  ;  the  filameutr  wave 
continually  to  and  fro  and  are  probably  tactile  in  fuiiction. 
In  many  forms,  too,  in  the  neighborhood  of  the  mouths  of  the 
ordinary  individuals  sac-like  pouches  occur,  in  which  the 
ova  undergo  their  development.  These  structures,  known  as 
ovicelh  (Eig.  116,  oc),  or  ooecia,  have  also  been  considered  modi- 
lied  individuals,  but  seem  rather  to  be  organs  of  the  ordinary 
individuals,  arising  as  a  pouching  of  their  walls.  Finally,  not 
iufrequently    certain    individuals    relinquish    their   nutritive 


Fio.  117.—^,  Lauva  op  PedkelUna  fafter  Hatschek)  ;  B,   CyphonauUs  (after 

Pkouho). 
ad  =  adhesive  orgau.  «  =  stomiicli. 

cal  =  calotte.  sh  =  sliell. 

cor  =  coroMu.  pyr  =  pyrifonn  organ.' 

function  and  serve  as  root-like  anchors  or  stem-like  supports 
for  the  entire  colony. 

As  regards  the  internal  structure  of  the  Gymnolwmata  it 
IS  unnecessary  to  add  anything  to  what  has  already  been 
stated  in  describing  the  general  characteristics  of  the  order 
Ectoprocta. 

Development  of  the  PoJyzoa.—The  larva  of  PcdkrUimt  (Fig. 
117,  A  ),  which  may  be  taken  as  a  type  of  the  Endoprncta,  is  a 
somewhat  donie-shapiul  organism,  the  summit  of  the  dome 
IxMug  occupied  by  an  apical  thickening  {cat)  bearing  a  tuft  of 
ciliji,  while  at  the  marmn  tlif»ro  iu  n  uf,.i 


•iliary  band,  ti 


iO 


I 


264 


INVERTEBRATE  MORPHOLOGY. 


corona  {cor).  The  cavity  of  the  dome  is  occupied  by  the  U- 
shaped  digestive  tract  (s),  the  mouth  aud  anus  both  opening 
Avithin  the  circle  formed  by  the  corona,  a  deep  depression, 
the  vestibule,  lying  between  the  two.  In  the  coelom  above 
the  floor  of  the  vestibular  depression  are  a  number  oi  meso- 
derm-cells,  and  also  a  cili.^ted  canal  composed  of  a  single  row 
of  perforated  cells  and  probably  excretory  in  function.  Upon 
one  surface  of  the  larva  between  the  marginal  ciliated  band 
and  the  apical  thickening  is  a  peculiar  glandular  organ  termed 
the  cement-gland  (pyr),  around  the  mouth  of  which  are  situ- 
ated a  number  of  strong  cilia. 

The  development  of  thir  larva  into  the  adult  form  is  accompanied  by  a 
number  of  remarkable  changes,  which  in  their  details  and  significance  are 
not  yet  tlioroughly  understood.  Tlie  larva  settles  upon  the  ventral  or  oral 
face  and  shortly  thereafter  one  wall  of  the  vestibule  becomes  pushed  over 
towards  the  other  and  eventually  unites  with  it,  the  original  vestibular 
cavity  becoming  divided  into  two  portions,  one  of  which  remains  in  con- 
nection with  the  surface  of  fixation  and  later  degenerates,  wliile  the  other 
has  opening  into  it  the  mouth  and  anus,  tliough  tlie  former  ()i)ening  at 
about  this  period  becomes  closed.  Later  a  remarkable  rotation  througli 
180°  of  the  digestive  tract,  together  with  tlie  portion  of  the  vestibule  in 
coniu'otion  with  it,  occurs,  the  portion  of  the  body  immediately  above  the 
point  of  fixation  elongating  to  form  the  stalk  of  tiie  adult,  becoming  at  the 
sami  time  filled  with  mesodermal  tissue.  The  mouth  opens  again  into  the 
vestibular  cavity,  the  tentacles  arise  from  the  wall  of  the  cavity  which 
later  opens  to  the  exterior,  tlie  adult  form  being  thus  assumed.  The  fate 
of  the  apical  tiiickening  and  of  the  cement-gland  is  uncertain  ;  they  have 
been  described  as  degenerating  without  taking  any  part  in  the  formaticm  of 
the  adult  organs,  tliough  it  has  been  suggested  tiiat  the  apical  thickening 
may  give  rise  to  the  nervous  system  of  the  adult. 

The  form  of  the  larvie  in  the  Eeto[)r()cta  is  subject  to  con- 
siderable moditication.  In  A/einhnaiiporii  and  some  other 
genera  the  larvti  is  known  as  the  ('i/pli())H(>tf<',s  (Vi^.  117,  /I), 
having  been  so  designated  before  its  life-history  was  eluci- 
dated. It  has  a  somewha*  triangular  outline  and  is  character- 
ized by  being  enclosed  in  a  bivalved  chitinous  shell  (fih).  At 
the  apex  of  the  triangle  is  the  apical  thickening  {col),  with  its 
elongated  cilia,  while  around  tl.<e  base  there  is  to  Vje  found  tlic 
corona  (cor).  A  W(>ll-develope(!  digestive  tract  is  ])re8ent.  both 
the  mouth  and  anus  upcning  upon  the  basid  surface  of  the  tri 
auLde.  aud  therefore  within  the  area  enclosed  bv  the  con)nn. 


TYPE  PROSOPTGIA.  265 

This  vestibule  is  a  deep  depression  of  the  oral  surface  of  the 
larva,  diflfenng  from  that  of  the  Fedicellina  larva  ouly  in  hav- 
ing an  arch-like  thickening  of  its  walls  (only  one  side  of  the 
arch  IS  represented  in  the  figure)  which  imperfectly  separates 
an   oral  portion  of  the  vestibule  from   a  posterior   or  anal 
portion,  a  glandular  depression  situated  in  the  roof  of  this 
latter  portion  constituting  the  adhesive  organ  (ad).     In  front 
ot  the  oral  vestibule  is  situated  a  ciliated  depression  from 
which   projects  a  tuft  of  long  cilia  and  which  appears  to 
correspond  to  the  cement-gland  of  the  Pedicellina  larva  and 
()  a  glandular  structure  in  the  moru  modified  Ectoprocta 
larvae  known  as  the  piriform  organ  {pyr),  by  which  name  it 
may  be  known  here.      The  similarity  of  this  larva  to  that  of 
Pedicelhna  is  clear,  the  details  of  organization  ox  the  two  forma 
ugreeing  part  for   part ;  in  other  Ectoprocta,  however,  great 
aifte.-ences  are  to  1  .  found.     In  the  genus  IJugnla,  for  exam- 
ple,the   arva  (Iig.  .18)  is  a  barrel-shaped  organism  at  the  one 
extremity  of  which  is  a  thickening, 
the  calotte  (cal),   which  appears    to 
correspond,  in  part  at  any  rate,  to 
the  apical  thickening  or  dorsal  organ, 
as  it  is  sometimes  termed,  of  Pedicel- 
linn  and  Cyphonantes.     The  sides  of 
the  barrel  are    formed    by   a  circle 
of  elongated  cells  forming  the  corona 
and    equivalent    to     the     marginal 
corona  of  the  other  larva? ;  it  does 
not,  however,  form  a  simple  band  in 
Bugnia,    but    its    cells     are    much 
sliorter  on  one  of  the  faces  of  the 
eiubryo    than  elsewhere,   producing 

a  Avell-marked  groove  at  the  apex  o^f  which  lies  the  pyriform 
organ  (pyr^  whose  homologies  in  Cyphonaute,  have  already 
l)eeu  pr.nt,;,|  out.  A  peculiarity  of  this  larva  is  the  entire 
al)sence  of  -i  uigestive  tract,  the  lower  end  of  the  barrel  being 
o<!cupied  by  a  depression,  the  adhesive  organ  (ad). 

Between  such  a  larva  as  that  just  described,  entirely  des- 
titute of  a  digestive  tract,  and  that  of  ( 'yphonaute,  intermediate 
"      -*-—-. '  xLbtdnou  in  tiiu  iarvff  oi  the  iJyciostomata, 


Km.  118.— Lauva  of  ntignla 
flabelldtit  (afiei-  luitiiom). 

Leltci'sasin  Fig.  117. 


I 


266 


INVERTEBRA  TE  MORPHOL  06  Y. 


in  which  the  digestive  tract  is  represented  by  a  yolk-laden 
mass  of  tissue,  having  little  resemblance,  however,  to  the 
differentiated  endodermal  tube  of  Pedicellitia.  The  occur- 
rence of  such  forms,  however,  shows  that  the  absence  of  the 
tract  in  Bugula,  etc.,  is  the  result  of  progressive  degeneration, 
such  larvjB  as  tliose  of  Pedicellina  and  Cyphonautes  represent- 
ing the  primitive  condition  more  nearly  than  the  remarkable 
larva  of  Bugula. 

The  traiisforniatioii  of  the  Ectoproctous  larvae  into  the  adult  is  even 
more  remarkable  than  that  of  Pedicellina.  Fixation  takes  place  by  the 
oral  surface,  the  i^dliesive  organ  being  evaginated  for  the  purpose,  and  is^ 
succeeded  by  a  degeneration  of  the  corona  and  pyriform  body.  In  Cypho- 
nautes the  digestive  system  completely  degenerates  likewise,  a  new  one 
being  formed  later,  the  tissue  in  the  neighborhood  of  the  apical  thickening 
taking  a  prominent  part  in  its  formation.  In  those  larvae  which  are  desti- 
tu(e  of  a  digestive  tract  one,  corresponding  to  the  second  one  of  Ci/p/io- 
nanien,  -'ovelops  after  fixation,  likewise  from  the  tissue  of  the  apical  thick- 
ening. I'i.v  exact  method  of  this  regeneration,  for  so  it  may  be  con- 
sidered, can  hardly  be  described  here  without  leading  to  a  recapitulation 
of  details  too  minute  for  the  scope  of  this  work.  It  may  be  remarked, 
however,  that  the  pi  lomena  do  not  seem  to  merit  the  designation  of  an 
alternation  of  generations,  as  might  at  first  sight  be  supposed,  but  are 
ratlier  simply  a  metamorphosis  the  significance  of  which  is  at  present 
decidedly  obscure. 

Baddinu  of  the  Polyzoa. — Ac  already  stated,  colony  formation  by  bud- 
ding is  a  characteristic  feature  of  the  Polyzoa,  Loxosoma  alone  not  pre- 
senting this  method  of  growth,  though  like  other  forms  it  reproduces  by 
budding,  the  buds,  however,  separating  at  an  early  stage  from  tlie  parent. 
In  the  Endoprocta  a  stolon  arises  from  near  the  point  of  fixaticm  of  the 
primary  individual  wliich  develops  from  the  ovum,  mesoderm  tissue  from 
tlie  stalk  of  tiiis  individual  migrating  into  the  stolon,  but  tiiere  is  no  pro- 
longation into  it  of  the  parental  endoderm.  At  a  more  or  less  definite  part 
of  the  stolon  tlie  ectodermal  cells  tiiicken  and  later  on  invaginate  towards 
the  centre  of  the  stolon.  This  invagination  becomes  surrounded  liy  meso- 
derm already  present  in  the  stolon,  and  later  differentiates  into  two  cavi- 
ties, one  of  which  retains  connection  with  the  exterior  fiii!l  mrms  tiic 
vestibular  chamber,  from  the  walls  of  which  tiie  tentacles  develop,  wiiiii 
the  other  becomes  the  digestive  tract,  its  original  connection  witli  tiie  ves- 
tibular cavity  becoming  the  anus,  the  mouth  developing  later  as  a  depres 
sion  of  the  floor  of  the  vestibular  cavity  wliieh  joins  the  stomach.  It 
is  interesting  to  note  that  from  the  ectodermal  invagination  the  nervous 
system  as  well  as  the  digestive  iraci  develops. 

In  tiie  Ectoproeta  practically  tht?  same  method  obtains  in  the  budding, 
thfiutrh  the  stolon  is  represented  by  tlie  tip  of  a  branoh  or  even  by  (lie 


TYPE  PROSOPTGIA. 


267 


tissue  in  the  neighborhood  of  the  mouth  of  the  zocBcium.  The  colony 
resulting  from  continued  budding  becomes  accordingly  as  a  rule  much  more 
oonipact  than  m  the  Endoprocta,  each  polypide  being  more  or  less  approxi- 
mated to  Its  predecessor. 

Closely  related  to  the  process  of  budding  is  that  of  regeneration,  also 
of  frequent  occurrence  among  the  Polyzoa.  Among  the  Endoprocta  Pedi- 
cellma  shows  the  process  in  a  periodical  though  not  simultaneous  moult- 
ing  ot  the  polypides,  new  ones  developing  from  the  tip  of  tiie  stalk  wiiich 
bore  the  amputated  polypide.  Here,  as  in  ordinary  budding,  the  tissues 
concerned  appear  to  be  ectoderm  and  mesoderm,  the  stalk  containing  no 
prolongation  of  the  original  endoderm. 

In  the  Ectoprocta,  however,  regeneration  is  carried  to  a  greater  extent 
In  examining  any  colony  of  Buyula,  for  example,  in  some  of  the  zoa'cia  in 
addition  to  the  polypide  a  brown  mass  may  be  seen,  the  so-called  "  brown 
body"  (Fig.  116,  66)  ;  in  others  the  brown  body  may  be  seen  without 
any  distinct  polypide.  This  body  is  the  result  of  the  degeneration  of  the 
digestive  tract  and  other  organs  of  the  original  polypide,  only  its  body- 
wall  or  endocyst  persisting,  from  which  new  organs  are  developed  and  the 
polypide  regenerated.  The  significance  of  this  process  is  not  clear,  but  it 
has  been  suggested  that  it  stands  in  relation  to  the  process  of  excretion 
the  formation  of  the  brown  body  occurring  in  forms  which  do  not  possess 
any  special  excretory  organs.  It  is  now  known  that  in  the  marine  Ecto- 
procta the  excretory  products  are  taken  up  in  part  by  the  cells  of  the 
stomach  and  c*cal  pouch,  a  fact  which  seems  to  harmonize  with  the  sue- 
gested  significance  of  the  brown  body. 

The  formation  of  a  new  polypide  from  ectoderm  and  mesoderm  appar- 
ently is  a  difficult  fact  to  explain  on  the  theory  of  the  g(>rm-layers  It  is 
possible,  however,  to  reganl  the  tissue  from  which  buds  arise  as  undiffer- 
entiated embryonic  tissue  passed  on  from  polypide  to  polvpide  and  trace- 
able back  to  the  embryonic  ti,s8  le  of  the  ovum.  In  the  foVmation  of  each 
polypide  a  certain  amount  of  the  t;  ,.ae  becomes  differHntiated  but  some 
still  retains  its  embryonic  character,  .i  continuation  of  the  buddin-  process 
bfiiiig  thus  possible. 

Affinities  of  the  Ihlysoa. -There  seems  to  be  little  room  for  doubt  but 
that  the  Endoprocta  represent  more  nearly  the  original  Polyzoa  than  do 
t he  Ectoprocta.  Their  colony  formation  is  of  a  more  simple  form  than 
mat  of  the  other  group,  they  possess  nephridia  which  are  wanting  in  the 
"lajority  of  the  Ectoprocta,  and  their  development  is  much  simpler  the 
i;;lily  modified  larva  of  the  marine  EctojH-octa  having  undoubtedly  been 
.lorived  from  one  approximating  in  structure  that  of  Pedicelliua,  Cmho- 
nantes  representing  a  stage  in  the  evolution. 

Similarities  have  been  traced  between  the  Pedirdlina  larva  and  the 
Anne  Hi  Irochophore,  and  it  is  not  improbable  that  this  may  have  been  the 
tme  derivation  of  the  group,  m  which  case  the  Polyzoa  are' to  be  re-ard^d 
as  forms  which  have  never  possessed  any  traces  of  metamerism.  but"8tan.i 
m  al.ni.t.  the  snme  relationship  to  the  Annelida  us  do  the  Kotifera 


268 


INVERTEBRATE  MORPHOLOGY. 


Another  view,  however,  Avhich  has  had  ardent  supporters  is  that 
which  recognizes  a  relationship  between  the  Polyzoa  and  Phoronis.  There 
is  a  lophophore  in  both,  likewise  a  U-like  bending  of  the  digestive 
tract,  and  the  nephridia  of  Phoronis  may  be  considered  comparable  to 
those  of  the  Endoprocta.  But  here  the  similarity  ceases.  The  anus  in 
Phoronis  is  outside  the  limits  of  the  lophophore  and  is  comparable  in 
position  with  that  of  the  Ectoprocta,  a  point  which  tells  against  tlii,, 
phylogeny  since  these  forms  have  been  shown  to  be  less  primitive  thiin  tl . 
Endoprocta.  If,  however,  this  phylogeny  should  prove  to  be  correct,  ii 
will  show  a  descent  for  the  Polyzoa  from  metameric  Annelids,  through  tlic 
Gephyrea,  since  it  is  to  this  group  that  Phoronis  seeras  to  be  most  nearly 
related. 


II.  Class  Brachiopoda. 

The  Brachiopoda  constitute  a  very  well-defined  group 
whose  present  poverty  in  species  is  in  striking  contrast  to  itn 
great  development  during  Palaeozoic  times.  Like  the  Poly- 
zoa they  possess  a  tentaculute  lophophore  (Fig.  120,  Ip)  Avhich 
usually  takes  the  form  of  two  exceedingly  elongated,  some- 
times spirally-coiled,  arm-like  processes  projecting,  one  on 
either  side,  from  the  anterior  portion  of  the  body,  and  fur- 
nished upon  their  outer  or  posterior  border  with  tentacles. 
The  body  is  usually  somewhat  short  and  stout,  and  prolonged 
posteriorly  into  a  peduncle  (pe)  or  stalk  Avhich  is  in  some 
cases  at  least  provided  with  adhesive  papilla)  and  serves  us 
an  anchor. 

The  most  characteristic  feature  of  the  Brachiopoda  is, 
however,  the  presence  of  a  bivalved  shell  (Fig.  119)  similar 
to  that  of  a  bivalve  Mollusk,  with  which  forms  the  Brachio- 
pods  were  until  comparatively  recently  associated.  From 
near  the  base  of  the  peduncle,  upon  the  dorsal  and  ventrul 
surfaces  of  the  body,  a  fold  of  the  body-wall  is  found,  Avhieli 
contains  a  cavity  in  communication  with  and  indeed  in  rriulits 
a  portion  of  the  euilojnic  cavity.  These  two  folds  are  of  sulii 
cieut  size  to  enwrap  or  enclose  the  body  and  the  lophoph(  re 
and  are  termed  the  mantle-lobes  (Fig.  120,  m),  the  space  between 
them  and  the  body  being  known  as  the  mantle-cavity.  Thev 
subserve  largely  if  not  entirely  the  function  of  respiration, 
the  portion  of  the  ccelom  which  they  contain  being  more  or 
less  divided  up  into  a  system  of  latMintp  through  which  tlm 


TYPE  PR080PYQIA. 


269 


hyemolymph  circulates.  Upon  the  outer  surface  of  each 
mantle-lobe,  and  formed  by  it,  is  a  valve  of  the  shell,  composed 
of  a  certain  amount  of  organic  matter,  but  largely  of  carbonate 
of  lime,  yiuce  the  mantle-lobes  are  dorsal  and  ventral  in 
position,  so  too  are  the  valves  of  the  shell,  and  consequently 
their  hinge-line  is  posterior  and  their  mouth  anterior.  In 
a  number  of  forms,  which  may  be  grouped  together  as  the 
suborder  Testicardines,  the  shells  along  the  hinge-line  are 
provided  with  interlocking  teeth,  a  true  hinge  being  present, 
the  peduncle  in  these  cases  perforating  a  backward  prolonga- 
tion or  beak  of  the  lower  valve.  In  a  few  genera,  however, 
forming  the    suborder  Acardines,  no  such  hinge  is  present, 


Fig.  119.— Dorsal  Valve  op  »'?;«n/e;',  showing  Arm  Skeleton  (after  Leunjs). 


the  peduncle  passing  out  between  the  two  valves  of  the  shell. 
Special  muscles  are  present  extending  from  one  valve  of  the 
shell  to  the  other  and  are  necessary  both  for  the  opening  and 
tlie  closing  of  the  shell,  and  furthermore  it  should  be  noted 
that  except  for  a  slight  difference  in  concavity  both  valves  of 
the  shell  are  similar  and  symmetrical. 

It  will  be  seen  by  comparing  the  various  facts  mentioned 
liere  witii  what  is  said  on  p.  827  regarding  the  shell  of  the 
bivalve  Mollusks  that  the  structures  in  the  two  groui)s  are 
very  different.  Tiiis  difference  is  emphasized  by  the  presence, 
ill  the  majority  of  the  Testicardines,  of  a  calcareous  support 
for  the  coiled  lophophore  attached  to  the  inner  surface  of  the 
dorsal  valve  (Fig.  119).  It  consists  of  a  pair  of  calcareous 
rods  which  project  downwards  and  forwards,  uniting  to  form 
a  transverse  arch,  and  may  give  rise  on  each  side  to  a  spirally- 
wound  ])r()cess  upon  which  the  coils  of  the  lophophore  rest. 

The  body-wall  is  ( omposed  of  an  outer  laver  of  ectoderm 


2 
^ 


270 


JN VEIiTEBHA TE  MOBPIIOLOO  F. 


from  which  numerous  papilho  or  in  some  cases  branching 
processes  arise,  projecting  into  corresponding  cavities  or 
tubes  in  the  substance  of  the  sholl-valves.  Bek)w  tlie  ecto- 
derm is  a  more  or  less  homogeneous  connective  tissue  con- 
taining cells  and  recalling  the  mesogkua  tissue  of  the  Coelen- 
terates.  Scattered  mascle-libres,  arranged  transversely  and 
longitudinally,  occur  in  the  mantle-lobes  and  in  the  body-wall, 
but  there  are  no  definite  muscular  layers  such  as  are  foui)d  in 
the  Annelida,  though  the  longitudinal  muscles  of  the  peduncle 
are  well  developed.  Special  muscles,  which  cannot  be  con- 
sidered differentiations  of  the  musculature  of  the  body-wall, 
traverse  the  ctelom  from  one  valve  of  the  shell  to  the  other, 
one  pair,  the  divaricators,  being  inserted  in  such  a  way  as  to 
cause  by  their  contraction  a  separation  of  tiie  two  valves, 
while  another  pair,  the  adductors  (Fig  120,  ant),  approximate 
them.  Other  muscles  also  occur,  si:  'h  as  the  adjustores, 
which  produce  lateral  ements  of  the  shell-valves,  and  pro- 

tractors and  retractors        ^.  120,  rm)  of  the  peduncle. 

The  coelom  is  lined  cy  a  peritoneal  epithelium  and  con- 
tains a  corpusculated  hsemolymph  which  is  driven  about 
through  the  coelomic  spaces,  and  the  lacuna)  in  the  mantle- 
folds  and  the  lophophore  which  communicate  with  them,  by 
the  contractions  of  the  body-wall  and  the  musculature,  there 
being  no  distinct  heart  or  blood-vessels.  A  dorso-ventral 
mesentery  which  slings  the  intestine  is  present  and  divides 
the  body-ccfilom  more  or  less  completely  into  two  lateral 
chambers,  and  furthermore  two  transverse  partitions  or  dis- 
ssepiments  occur  in  several  forms  and  divide  the  coelom  into 
iintevior,  middle,  and  posterior  compartments,  an  arrangement 
recalling  the  metamerism  of  such  a  form  as  Sagitla  (p.  1  37). 

The  mouth  opens  at  the  anterior  end  of  the  body  between 
the  two  lophophoric  arms  and  leads  into  a  short,  somewhat 
muscular  oesophagus,  which  posteriorly  communicates  with  a 
stomach-like  dilatation  (Fig.  120,  i)  into  which  open  the 
•ducts  of  one  or  more  pairs  of  branching  tubular  glands — the 
so-called  liver  or  digestive  glands  {J).  Behind  the  stomach  lies 
the  intestine,  which,  in  most  of  the  Ecardines,  such  ;is  Lingula, 
bends  upon  itself  and  opens  into  the  mantle-cavity  in  the 
mid  dorsal  line  near  the  anterior  end  of  the  body.     In  Crania, 


TYPE  PROSOPYGIA. 


271 


however,  it  opens  posteriorly,  while  iu  TerehratuUm,  Argiope, 
ami  WaUheimia,  iu  fact  iu  all  the  Testicardines,  it  euds 
bliuclly,  the  auus  boiug  wautiufj. 

The  nervous  system  consists  of  au  cjBso[)hageal  riuf,'  lying 
iu  the  connective  tissue  substance,  the  lower  portion  being  in 
connection  with  the  ectoderm  and  slightly  swollen,  represent- 
ing  probably  the  subcesophageal  ganglion  of  the  Annelida ; 


<) 


Fig.  120.— Stuucture  op  TerebratuUna  septentrionalis. 
am  =  adductor  muscle.  ne  =  ncphridium. 

i  =  intestine.  ov  —  ovary. 

I  =  liver-lobes.  pe  =  peduncle. 

Ip  =  lophophore.  rm  =  retractor  muscle. 

m  =  mantle.  g  =  shell. 

a  similar  swelling  in  the  dorsal  portiou  of  the  ring  reju-esents 
the  supraoesophageal  ganglion,  and  iu  addition  there  are  usu- 
ally two  further  lateral  ganglion-like  swellings.  Nerves  pass 
off  from  the  upper  ganglion  to  the  lophophore  and  other 
regions,  and  from  the  lower  one  to  the  mantle,  muscles,  etc., 
l)oth  sets  terminating  in  the  superficial  layers  of  the  lopho! 
l)hore-tentacles  or  of  the  mantle  in  a  network  of  ganglion 
cells  and  fibres.  No  trace  of  a  ventral  nerve-cord  in  addition 
to  the  subcesophageal  ganglion  is  present. 

Sense-organs  are  but  poorly  developed,  neither  eyes  nor 
auditory  organs  occurring.  The  tentacles  on  the  lophophoric 
arms  are  in  all  probability  sensory,  as  indicated  by  their  rich 
nerve-supply,  and  the  papillae  of  th«  mantle-ectoderm  whioli 


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272 


INVERTEBRA TE  MQRPHOLOG  Y. 


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project  into  the  canals  of  the  shell  have  been  stated  to  be 
sensory,  containing  an  axial  nerve-fibre  terminating  in  a  sen- 
sory cell. 

The  nephridia  (Fig.  120,  we)  are  represented  by  two  or 
four  {Bhyrwhonella)  funnel-shaped  short  tubes  which  open  by 
a  fimbriated  mouth  at  one  extremity  into  the  coeloraic  cavity 
and,  rapidly  narrowing  towards  the  outer  end,  open  by  a  small 
pore  into  the  mantle-oavity.  In  addition  to  their  probable 
excretory  function,  th'^se  structures,  as  in  some  of  the  Anne- 
lida, serve  also  as  ducts  for  the  passage  to  the  exterior  of  the 
reproductive  elements.  These  are  derived  from  the  coelomic 
peritoneum  and  form  branching  masses  (Fig.  120,  ov)  lying  in 
some  cases  in  the  coelomic  spaces  of  the  mantle,  or  in  addition 
extending  into  the  body,  as  in  most  Ecardiues,  or,  as  in  Tere- 
braMina,  confined  to  this  region.  Most  of  the  Brachiopods 
are  bisexual  apparently,  though  it  is  possible  thai  Lingida 
and  perhaps  some  other  forms  may  be  hermaphroditic,  the 
male  and  female  elements  maturing  at  different  times. 

Development  and  Affinities  of  the  Brachiopods. — The  Testi- 
cardines  are  characterized  by  the  occurrence  of  a  free  larval 
stage  destitute  of  a  shell.  In  Argiope  (Fig.  121)  it  is  appar- 
ently divided  into  four  segments,  the  most 
anterior  of  which  bears  two  eye-spots  and 
assumes  an  umbrella-like  form,  long  cilia 
projecting  from  the  margin.  The  third 
segment  develops  two  folds  which  enclose 
the  posterior  segment  and  bear  on  their 
margin  bunches  of  setjc  inserted  in  seta- 
sacs  and  recalling  the  sette  of  certain  Annelid 
larvae.  After  swimming  about  for  a  time 
the  larva  settles  down  and  fastens  itself  by 
the  posterior  segment  and  the  mantle-lobes 
turn  forward  to  enclose  the  anterior  seg- 
ments. The  posterior  segment  becomes  the 
peduncle  of  the  adult,  and  the  shell  de- 
velops on  the  surface  of  the  mantle-lobes,  whose  bunches  of 
setio  are  thrown  oflf.  The  mouth  makes  its  appearance  only 
after  fixation  just  ventral  to  the  eye-spota,  and  around  it  there 
develojm  a  ring  of  tentacles  jdaced  somewhat  obliquely,  and 


Fio.   131.— LxnvA 
OK   Argiope   (after 

KoWALBWMKI). 


TYPE  PBOSOFTOIA. 


373 


later  elongating  laterally  to  form  the  coiled  lophophore  with 
its  numerous  tentacles. 

The  early  stages  of  the  development  of  the  Ecardines  is 
not  known,  but  in  Lingula  the  larva  is  free-swimming  long 
after  the  shell  has  formed,  the  peduncle  being  late  in  develop- 
ing. In  this  form  also  the  lophophore  arises  as  a  circle  of 
tentacles  surrounding  the  mouth  and  subsequently  elongates 
laterally. 

The  affinities  of  the  BracLiopods  have  long  been  an  open  question- 
They  were  by  early  writers  regarded  as  Mollusca,  later  as  Annelida  or 
closely  related  to  thai  group,  but  are  now  usually  considered  to  be  more 
nearly  related  to  the  Polyzoa  than  to  any  other  forms  and  to  be  most 
properly  associated  with  them,  the  general  likeness  of  a  young  Lingula,  for 
instance,  to  a  Polyzoan  being  very  striking.  The  presence  of  the  mantle- 
lobes  and  the  shell  seem  to  mark  the  Brachiopoda  as  something  far  removed 
from  the  other  members  of  tiie  type  Prosopygia,  but  it  must  be  remembered 
that  in  the  larval  Ectoproctous  Polyzoa  the  corona  behaves  in  a  manner 
closely  similar  to  the  Brachiopod  mantle  and  it  is  not  impossible  that  the 
two  structures  may  have  something  in  common. 

Another  distinguishing  feature  of  tha  Brachiopods  is  the  indication  of 
a  segmentation.  The  presence  of  two  dissepiments  and  in  Rhynchonella  of 
two  pairs  of  nephridia  certainly  suggests  metamerism,  hut  objection  has 
been  raised  to  the  dissepiments  having  any  metameric  significance,  on  the 
ground  that  they  do  not  bear  the  proi)er  r«lationsiiips  to  the  body  axis  to 
be  regarded  as  comparable  to  the  dissepiments  of  the  Annelida.  It  ha* 
been  stated  by  some  authors  as  a  characteristic  of  the  Pro.sopygia  that 
tlieir  body  axis  is  bent  upon  itself  so  that  the  two  ends  are  approximated 
and  one  surface,  the  dorsal,  is  almost  obliterated,  while  the  other,  the 
ventral,  is  very  much  enlarged,  as  seems  to  be  actually  the  case  in 
Phoronis.  It  must  be  remembered,  however,  that  the  terms  dorsal  and 
ventral  are  not  to  be  defined  by  reference  to  the  digestive  tract  alone,  but 
otner  structures  have  also  to  be  taken  into  consideration.  Thus  it  is  quite 
l)ossiblo  that  in  the  Polyzoa  the  approximation  of  the  mouth  and  anus  indi- 
cates simply  a  bending  of  tin  digestive  tract  and  a  migration  forwards  of 
the  anus  and  not  necessarily  a  bending  of  the  body  axis;  and  the  varying 
position  of  the  anus  in  the  Ecardinate  Brachiopods  tends  to  support  this 
idea,  the  Ijody  axis  in  Crania  with  .i  terminal  anus  certainly  besiug  similar 
to  that  of  Lingula,  in  which  the  anus  lies  far  forwards.  In  this  connec- 
tion, too,  the  arrangement  in  Sipmicu/us  is  of  interest,  the  nerve-cord  show- 
ing the  usual  relations  to  the  body  axis,  while  the  digestive  tract  is  bent 
upon  itself  and  the  anus  opens  fai'  in  front  of  the  posterior  extremity,  in 
the  Sipunculacea  there  can  be  no  question  of  a  difforonco  of  the  body  axis 
in  the  various  forms,  and  it  seems  probable  that  the  supposed  bending  of 
the  body  axis  in  the  Prosopygia  has  not  really  occurred,  but  that  there 


,n 


&i 


■TP 


274 


INVERTEBRATE  MORPHOLOOY. 


has  been  simply  a  bending  of  the  digestive  tract  and  a  migration  forwards 
of  the  anus. 

If  this  be  the  correct  way  of  regarding  the  matter,  then  there  is  no 
reason  for  disputing  the  homology  of  the  dissepiments  of  the  Brachiopoda 
with  those  of  tiie  Annelida,  and  the  idea  that  they  represent  a  metamerism 
is  borne  out  by  the  arrangement  of  the  two  pairs  of  nephridia  of  RJiyn- 
■chonella.  The  question  is  then.  Does  the  metamerism  of  the  Brachiopods 
indicate  a  descent  of  the  Prosopygia  from  metameric  ancestors,  i.e.,  from 
Annelids  through  Gephyrean-like  forms,  or  is  it  a  structural  feature  inde- 
pendently acquired  by  the  Brachiopods  ?  The  evidence  at  our  disposal  is 
not  sufficient  for  the  solution  of  this  problem,  and  all  that  can  be  main- 
tained is  that  a  very  close  relationship  exists  between  the  Polyzoa  and  the 
Brachiopoda. 


'Ii    te« 


SUBKINGDOM   METAZOA. 

TYPE  PROSOPYGIA. 

1.  Class  Polyzoa.— Small,  usually  colonial  forms ;  lophopbore  circular  or 
horseshoe-shaped ;  no  bivalve  shell ;  no  mantle-lobes. 

1.  Order  Endoprocta.—Houih  and  anus  both  within  the  area  enclosed 

by  the  lophophore.    Loxosoma,  Pedicellinu,  Ascopodaria, 
Urnatella. 

2.  Order  Ebto^rocto.— Anus  outside  the  area  enclosed  by  the  lopho- 

phore. 

1.  Suborder  P^yZactotowato. —Fresh- water  forms  ;  lophophore 

usually  horseshoe  shaped  ;  epistome  present.  Ftederi- 
cella,  Alcyonella,  Lophopus,  Cristatella. 

2.  Suborder  %»iwotema^a.— Usually  marine;    lophophore  cir- 

cular ;  no  epistome. 
Mouth  of  zooecium  without  bristles  or  operculum  (Cydo- 

stomata).     Crista. 
Mouth  of  zooecium  usually  surrounded  by  bristles  which 

close  over  it  (Ctenostomata).    Paludicella,  Alcyonidium. 
Mouth  of  zooecium  provided  with   an  operculum  {Chilo- 

stomata).    Membranipora,  Bugula.  Flustra,  Scrupocel- 

laria. 
II.  Class  Brachiopoda.— Non-colonial  and  of  moderate  size ;  lophophore 

usually  arm-like  and  coiled  into  a  spiral ;  mantle-lobes 

and  bivalve  shell  present. 

1.  Order  Ecardines.  —  Shell-valves  not  hinged  ;    peduncle  protrudes 

between  the  valves  ;  anus  present.    Lingula,  Crania. 

2.  Order  Testimrdines.—^hnW-ynXsa^  hinged  ;  peduncle  when  present 

protruding  tiirough  perforation  in  the  ventral  shell ;  anus 
wanting.  Terebratula,  Waldheimia,  Aryiupe,  liliyncho- 
nella. 


TYFE  FHOSOPYGIA. 


275 


LITERATURE. 

4 

POLYZOA. 

G  J.  AUman.     A  Monograph  of  the  Fresh-icater  Polyzoa.    London,  1856. 

T.  Hincks.     A  Biatoi'y  of  the  British  Marine  Polyzoa.    London,  1880. 

H.  Nitsche.     Beitrdge  zur  Kenntnisa  der  Bryozoen.    Zeitschr.  fUr  wissensch. 

Zoologie,  XX,  1869  ;  xxi,  1871  ;  xxv,  Suppl.,  1875, 
A.  Hyatt.     Observations  on  Polyzoa.    Suborder  Phylactolamata.    ProceedingR 

Essex  Institute,  iv  and  v,  1866-68. 
S.  F.  Harmer.     On  t/ie  Structure  and  Development  of  Loxosoma.    Quarterly 

Jouni.  Microscop.  Scieace,  xxv,  1885. 
C.  B.  Davenport.     Papers  in  Bulletin  of  the  Museum  of  Comp.  Zoology,  xx» 

1890  ;  XXII,  1891  ;  and  xxiv,  1893. 


BRACHIOPOnA. 

E.  8.  Korse.     On  the  Systematic  Position  of  the  Braehiopoda.    Proceed.  Boston 

Soc.  Nat,  History,  xv,  1893. 

W,  K.  Brooks,  The  Development  of  Lingula.  The  Chesapeake  Zoolog,  Labo- 
ratory.    Scient.  Results  of  the  Session  of  1878. 

J,  F.  van  Bemmelen.  Unters,.  .angen  iiber  dew  anatomischen  und  histologischen 
Ban  der  Braehiopoda  testicardinia.    Jenaische  Zeitschr.,  xvi,  1883. 

M.  A.  Sohulgin.  Argiope  Kowalewskii.  Ein  Beitrag  zur  Kenntniss  der  Braehio- 
poden.     Zeitschr.  fllr  wissensch.  Zoologie,  XLi,  1884. 

H.  0.  Beyer  A  Study  of  the  Structure  of  Lingula  (Glottidia)  pyramidata. 
Studies  from  the  Biolog.  Labor.  Johns  Hopkins  University,  iii,  1886. 

F.  Blochmann.     Untersuchungen  iiber  den  Ban  der  Brachiopoden.    Jena,  1892. 


*i76 


INVERTEBUATB  MORPHOLOGY, 


CHAPTER  XIL 

TYPE    MOLLUSCA. 

While  the  Annelida  are  characterized  by  an  elongated 
form  of  body,  the  Mollusca  present  the  opposite  condition, 
being  compact,  nou-metameric  organisms,  though  at  the  same 
time  primitively  bilateral  in  the  arrangement  of  their  organs. 
Upon  the  external  surface  of  the  body  a  cuticular  secretion 
is  formed  in  which  usually  particles  of  carbonate  of  lime 
are  deposited,  a  calcareous  shell  being  thus  developed,  which 
encloses  more  or  less  perfectly  the  soft  body,  assuming, 
however,  very  different  forms  in  the  various  groups.  It  is 
essentially  a  dorsal  structure  developed  in  the  majority  of 
forms  from  a  depression  on  the  dorsal  surface  of  the  body 
— the  shell-gland  (Fig.  122,  /) — and  in  some  forms  may  be 
entirely  confined  to  this  area.  Usually,  however,  a  circular 
or  bilateral  fold  of  the  body,  the  mantle  (c),  arises  peripheral 
to  the  margins  of  the  shell-gland  and  extends  downwards 
towards  the  ventral  surface,  and  the  growth  of  the  shell  may 
accompany  that  of  the  mantle-fold,  so  that  the  entire  body  is 
enclosed  by  or  may  be  retracted  within  the  greatly-developed 
shell.  Even  in  cases,  however,  in  which  the  shell  is  but 
slightly  developed  *^^he  mantle-folds  retain  their  development, 
forming  a  marked  structural  feature  of  the  Mollnsca,  and  en- 
closing a  more  or  less  spacious  cavity,  the  mantle-cavity,  in 
which  lie  the  respiratory  organs  and  into  which  the  intestine 
and  nephridia  and  reproductive  ducts  open. 

The  body-wall  is  formed  of  an  external  layer  of  eetodern), 
below  which  a  more  or  !ess  thick  layer  of  muacle-tissne  is 
found  whose  fibres  sometimes  show  the  arrangement  in  cir- 
cular and  longitudinal  layers  characteristic  of  the  Annelida, 
but  usually  the  simplicity  of  this  arrangement  is  interfered 
with  by  a  development  of  connective  tissue  in  which  irregu- 
larly-arranged muscle-bundles  lie.     Upon  the  ventral  surface 


li 


TYPE  MOLLUSC  A. 


277 


of  the  bodj  there  is  a  special  thickening  of  the  muscle-tissue 
to  form  a  "foot"  (Fig.  122,  p\  which  assumes  a  great  variety 
of  forms,  and  special  muscles  are  developed  for  its  protrac 


Fig.  122. 


ope       P  ^i        Jc       'I 
-Diagrams  showing  the  Ahrangement  op  the  Organs  in  an 
Ideal  Mollusk  (after  Lankestek). 


a  z=  tentacle. 
b  =  head. 

c  =  margin  of  mantle 
d  =  margin  of  shell. 
e  =  edge  of  body. 
/=  edge  of  shell  depression. 
g  =  shell. 

gc  =  cerebral  ganglion. 
gpe  =  pedal  ganglion. 
gpl  7=  pleural  ganglion. 
A  =  osphradiiim. 


i  =  ctenidiiini. 

k  =  reproductive  pore, 

I  =  uephridial  pore. 
m  =  anus, 
n  and  p  —  foot. 

r  =  coelom. 

«  =  pericardium. 

t  =  testis. 
u  =  nephridiuni. 
«  =  ventricle  of  heart. 
el  =  liver. 


tiou  or  retraction  when  this  is  necessary,  as  well  as  for  the 
closure  of  the  shell  in  those  forms  (Pelecypoda)  in  which  it  is 
II  bilateral  structure. 

The  coelom  is  in  some  forms  a  relatively  spacious  cavity, 
traversed,  however,  even  in  these  cases  by  thin  bands  of  con' 


278 


INVERTEBRA  TE  MORPUOLOG  T 


nective  tissue,  but  more  usually  it  is  reduced  to  a  system  of 
lacunar  spaces  (a  so-called  schizocoel)  by  the  development  of 
muscle-bundles  traversing  it  in  various  directions.  A  special 
portion  of  it  (the  so-called  enterocoel)  is,  however,  always  en- 
closed in  definite  walls  lined  by  a  peritoneal  layer  of  cells,, 
forming  a  cavity,  the  pericardium  (Fig.  122,  s),  which  lies  nor- 
mally near  the  dorsal  surface  of  the  body,  containing  the 
heart  and  having  the  inner  ends  of  the  nephridia  (w)  opening 
into  it.  The  blood  vascular  system  consists  of  a  primitively 
three-chambered  heart  (Fig.  122,  r)  enclosed  within  the 
pericardium  and  composed  of  a  tubular  muscular  ventricle 
and  two  wing-like  auricles  which  open  into  the  ventricle, 
their  openiugg  being  guarded  by  valves  which  prevent  regur- 
gitation. From  the  anterior  and  posterior  extremities  of  the 
ventricle  aortas  arise,  which,  however,  as  a  rule  soon  lose 
themselves  in  the  coelomic  lacunae.  There  is  thus  no  distinc- 
tion between  the  blood  and  pseud-hsemal  fluids  in  the  Mol- 
lusca,  since  the  blood  vascular  system  is  not  closed.  The 
blood  is  a  colorless  fluid  in  which  numerous  amceboid  cells 
float  and  which  holds  in  solution  a  substance,  hsemocyanin, 
which  subserves  a  respiratory  function  in  a  manner  similar 
to  the  hsemoglobiu  of  the  Vertebrata. 

The  heart  is  a  systemic  heart,  as  is  usual  in  the  Invertebrata,  and  con- 
tains only  aerated  blood,  which  it  propels  through  the  lacunae  of  the  body. 
Returning  from  these,  the  blood  passes  either  directly  to  the  respiratory 
organs  or  branchiae,  or  else  a  greater  or  less  portion  of  it  traverses  first  the 
walls  of  the  nephridia  and  then  passes  to  the  branchiae.  From  these,  in 
which  it  is  aerated,  it  is  received  into  the  auricles,  and  on  their  contractioh 
is  forced  into  the  ventricle. 

In  some  Mollusca  respiration  is  carried  on  by  tbe  general 
surface  of  the  body,  but  such  an  arrangement  must  be  re- 
garded as  the  exception.  As  a  rule  special  respiratory  or- 
gans are  present  in  the  form  of  one  or  more  pairs  of  plume- 
like  processes  {ctenidia)  of  the  body-wall  (Fig.  122,  i)  lying 
free  in  the  mantle-cavity.  They  have  various  forms  in  the 
different  groups,  but  consist  essentially  of  a  central  axis  con- 
taining an  afferent  and  efferent  canal  for  the  blood  and  bear- 
ing a  single  or  double  series  of  filaments  whose  walls  are  thin 
and  whose  ectoderm  is  ciliated,  an  interchange  of  the  gases 


TYPE  MOLLUSC  A. 


279 


of  the  blood  with  those  of  the  water  contained  in  the  mantle- 
cavity  being  thus  readily  effected,  a  renewal  of  the  water  con- 
stantly  taking  place  in  consequence  of  the  action  of  the  ecto- 
dermal cilia.  The  thin-walled  mantle-fold  is,  however,  a  very 
efficient  adjunct  to  the  branchiae  in  respiration,  the  spaces 
within  the  fold  being  portions  of  the  lacunar  coelom  and  con- 
sequently containing  blood  ;  indeed  in  some  cases  the  mantle 
assumes  completely  the  respiratory  function,  the  ctenidia 
becoming  rudimentary. 

The  digestive  tract  is  a  usually  more  or  less  coiled  or  con- 
voluted tube  in  which  various  regions  may  be  distinguished. 
In  a  few  forms,  characterized  either  by  the  slight  develop^ 
ment  of  the  mantle  or  its  development  as  two  lateral  folds 
the  anus  is  terminal  in  position,  but  when  an  extensive  cir- 
cular mantle-fold  is  developed  the  intestine  bends  upon  itself 
and  opens  upon  the  side  of  the  body,  more  or  less  anteriorly 
into  the  mantle-cavity.  Immediately  behind  the  mouth  chi' 
tiuous  teeth  (Fig.  123,  hj)  are  usually  developed  in  the  wall  of 


Fig.  123. -Buccal  Mass  and  Radula  of  Helix  (after  Howes). 
ce  =  cerebral  ganglion.  re  =  nidular  cartilage. 


hj  —  horny  jaw. 
tm  =  intrinsic  muscles. 
pgl  =  pedal  gland. 


rd  =  radula. 
I'd'  =  radular  sac. 
St  =  opening  of  salivary  gland. 


the  pharynx,  and  behind  these  a  large  muscular  thickening 
generally  occurs,  the  buccal  mass,  in  connection  with  which 
is  developed  a  characteristic  Molluscan  structure,  the  lingual 
ribbon  or  radula  (rd).  The  sides  and  floor  of  the  pharynx  in 
tins  region  are  largely  thickened  by  the  development  in  them 
of  muscular  tissue  (wi).  The  thickening  of  the  floor  is  usually 
so  extensive  as  to  project  into  the  pharyngeal  cavity,  forming 


I 


IB 


Jis 

m 


i 


liltt 


280 


INVERTEBRA TE  MORPHOLOG  Y. 


the  so-called  tongue,  and  in  addition  to  the  muscular  tissue 
two  or  mox-e  pieces  of  cartilage,  the  radular  cartilages  {re),  are 
frequently  found  in  it.  Oovering  the  tongue  is  a  stout  chi- 
tinous  membrane,  the  basal  membrane,  which  bears  upon 
its  surface  a  usually  enormous  number  of  chitinous  teeth 
arranged  in  transverse  rows,  so  that  the  basal  membrane 
and  the  teeth,  together  constituting  the  radula  {rd),  recall 
somewhat  the  appearance  of  a  flat  tile.  Behind  the  tongue 
the  floor  of  the  pharynx  is  produced  downwards  and  back- 
wards into  a  pouch,  the  radula-sac  {rd'),  sometimes  of  con- 
siderable length,  into  which  the  radula  is  continued  on 
the  ventral  wall,  the  cells  {odontoblasts)  which  form  the  teeth 
as  a  cuticular  secretion,  lying  at  the  bottom  of  the  sac.  The 
tongue,  with  its  radula,  can  be  protruded  to  a  greater  or  less 
extent  from  the  mouth  b}'  special  protractor  muscles,  and  its 
intrinsic  muscles  serve  to  give  it  a  slow  licking  movement, 
whereby  the  radula  acts  as  in  the  manner  of  a  flle  or  rasp 
upon  the  object  with  which  it  is  in  contact.  Owing  to  this 
action  the  radula  is  continually  being  worn  away  at  its  anterior 
end,  but  is  also  continually  being  pushed  forward  upon  the 
tongue  by  the  addition  of  new  teeth  to  its  posterior  portion 
at  the  base  of  the  radula-sac. 

In  connection  with  the  digestive  tract  various  glands  are 
usually  present,  of  which  the  most  constant  are  the  salivary 
glands  and  the  "  digestive  glands."  The  former  open  into 
the  pharynx  and  in  some  cases  reach  extensive  devolopment ; 
their  function  for  the  most  part  is  but  little  understood,  but 
in  some  predaceous  Ga^teropods  their  secretion  has  been 
found  to  contain  a  considerable  amount  of  free  sulphuric  acid 
which  probably  serves  to  soften  the  calcareous  shell  of 
Echinoderms  and  other  MoUusca  which  serve  these  forms  as 
food.  The  "  digestive  glands  "  open  into  a  dilated  portion  of 
the  intestine,  usually  termed  tlie  stomach,  and  are  usually 
paired,  voluminous,  much-branched  tubular  glands  whose 
function  is  indicated  by  the  name  applied  to  them.  They 
seem  to  be  the  physiological  representatives  of  the  pancreas 
of  the  Vertebrata,  and  to  secrete  digestive  ferments  which 
are  brought  into  contact  with  the  food  in  the  stomach. 

The  nervous  system  of  tne  Mollusca  (Fig.  124),  in  accord- 


TYPE  MOLLUSC  A. 


281 


ance  with  the  absence  of  metamerism,  lacks  the  ladder-like 
arrangement  which  characterizes  the  Annelida.     Nevertheless 
there  are  two  ganglionic  masses,  each  in  typical  cases  com- 
posed  of  two  ganglia  which  may  be  homologized  with  the  su- 
pra^scphageal  and  the  most  anterior  suboesophageal  ganglia 
of  the  metameric  forms,  and  are  known  respectively  as  the 
<.6r.W  (Fig.  124,  ce)  and  pedal  (pe)  ganglia.     The  foimer  lies 
above  the  oesophagus  behind  the  buccal 
mass    and  is  connected  by    nerve-cords 
termed  connectives,  surrounding  the  oeso- 
phagus,  with   the   pedal   ganglion.     The 
cerebral  ganglion  gives  off  nerves  which 
pass  to  the  eyes  and  otocysts  {ot)  and  to 
the   tentacular   structures   of  the  head, 
while   the   pedal    ganglion    receives  its 
name  from  the  fact  that  it  sends  nerves 
to  the  muscular  mass  forming  the  foot. 
In  addition  to  this  system  of  nerves  and 
ganglia  there   is   another  system   highly 
developed  in  the  Mollusca  which  would 
seem  to  correspond  to  the  visceral  system 
found  in  some  other  forms.     It  consists  bu  =  buccal  gauglia. 
typically  of  a  pair  of  pleural  ganglia  (pi),    ^^  =  cerebral  guuglion. 
one  of  which  lies  upon  either  side  of  the    "'  "  *'^''^^''*- 
pharynx,   being   united    by    connectives 
with  both  the  cerebral  and  pedal  gauglia. 
From  each  pleural  ganglion  a  nerve-cord 
passes  backwards  to   unite  with  one  or 
more  visceral  ganglia  {vi),  situated  below  the  intestine  near  its 
posterior  termination,  and  on  each  of  these  visceral  cords  a 
ganglion  occurs,  the /janeto?  ganglion  {pa\  from  which  nerves 
imss  to  the  gills,  or  rather  to  the  sense-organ  which  is  in  con- 
nection with  them.     The  pleural  ganglia  innervate  especially 
the  mantle  and  the  body-wall  behind  the  head,  the  visceral 
ganglia  send  branches  principally  to  the  various  viscera,  while 
the  parietal  gauglia,  iu  addition  to  the  branches  which  go  to 
the  gills  and  their  sense-organs,  also  assist  in  the  innervation 
of  the  mantle. 

Besides  these  principal  ganglia,  however,  others  connected 


Fig.  124.— Diagram  of 
Nervous  System  of 

-MOLLUSK. 


pa  =  parietal  gangliou. 
pe  =  pedal  ganglion. 
pi  =  pleural  gauglion. 
VI  =  visceral  ganglion. 


'W  UM 


282 


INVEHTEBRATE  MOliPHOLOOY. 


with  either  the  cerebro-pedal  or  pleuro-visceral  system  raaj 
be  developed,  the  most  constant  of  which  are  the  buccal  gan- 
glia {bv)  which  lie  at  the  sides  of  or  more  usually  below  the 
buccal  mass  which  they  innervate  and  are  united  by  commis- 
sures with  the  cerebral  ganglia.  Two  nerve-rings  in  such 
cases  surround  the  oesophagus,  i.o.,  that  formed  by  the  cere- 
bro-pedal and  that  of  the  cerebro-buccal  connectives. 

This  description  has  reference  oidy  to  what  may  be  con- 
sidered a  typical  condition,  and  it  must  be  remembered  that 
frequent  modifications  of  it  may  occur.  In  the  Gasteropods, 
for  example,  in  which,  in  accordance  with  the  development  of 
a  circular  mantle-fold,  the  anus  comes  to  lie  on  the  anterior 
portion  of  the  body-wall,  a  peculiar  crossing  of  the  pleuro- 
visceral  commissures  occurs  in  some  cases,  and  as  a  result 
what  was  originally  the  right  parietal  ganglion  comes  to  lie 
upon  the  left  side  of  the  body  and  the  original  left  ganglion 
upon  the  right  side.  Further  consideration  of  this  arrange- 
ment may,  however,  be  postponed  until  the  Gasteropods  are 
under  discussion.  Mention  should,  however,  be  made  here 
of  another  not  unfrequent  modification  of  the  typical  arrange- 
ment of  the  nervous  system,  which  consists  in  the  concentra- 
tion of  the  ganglia  and  the  shortening  of  the  various  connec- 
tives. This  may  affect  only  the  cerebral,  pedal,  and  pleural 
ganglia,  bringing  them  into  close  approximation,  or,  as  in  some 
Cephalopods,  the  visceral  ganglia  may  also  be  carried  forward 
so  that  all  the  principal  ganglia  are  united  into  a  single  lobed 
mass  closely  surrounding  the  oesophagus  behind  the  pharynx. 
This  condition  constitutes  of  course  the  culmination  of  the 
concentration  process,  but  various  gradations  of  it  are  to  be 
found  in  the  different  groups. 

Sense-organs  are  as  a  rule  well  developed  in  the  Mollusca, 
and  descriptions  of  many  of  them  may  be  more  conveniently 
given  in  connection  with  the  detailed  account  of  the  various 
groups.  The  general  ectoderm  of  the  mantle  and  body-wall 
has  scattered  in  it  numerous  sensory  cells  v/hicli  may  become 
specially  aggregated  at  certain  points  to  form  definite  sense- 
organs.  Thus  tentacles  are  frequently  borne  upon  the  head 
which  are  tactile  or  in  some  cases  olfactory  in  nature,  and  at 
the  bases  of  the  gills  special  aggregations  of  sensory  cells  are 


m 


TYPE  MOLLUSC  A. 


283 


185.-  Otocyst    op    Ptero- 
trachea  lafter  Glaus). 


to  be  found  formin-  the  osphradia,  also  supposed  to  have  an 
olfactory  function.  Otocysts  (Fig.  125)  are  present  in  nearly 
all  the  groups,  consisting  of  a  vesicle  with  a  membranous  wall, 
the  interior  of  which  is  lined  by  sensory  cells  bearing  bunches 
of  hairs  projecting  into  the  vesicle 

which  contains  one  or  more  calca-  ^/^f 

reous  otoliths.  An  auditory  func- 
tion has  usually  been  attributed  to 
these  organs,  but  it  seems  probable 
that,  as  in  the  lower  forms  (see  p. 
82),  they  are  rather  to  be  regarded 
as  organs  of  an  equilibrium -sense, 
and  in  fact  that  they  subserve  such 
a  function  in  part  at  least  has  been 
experimentall}'  determined  in  the 
Cephalopods. 

Eyes  are  very  frequently  present 
and  in  the  Cephalopods  reach  an 
exceedingly  high  development.  They  occur  usually  upon  the 
head,  but  may  also  be  found,  as  in  the  Pelecypoda,  upon  the 
edge  of  the  mantle,  or  even  on  the  dorsal  surface  of  the  body, 
as  in  the  Pulmonate  Onchidium.  They  vary,  however,  so 
much  in  structure  in  different  groups  that  an  account  of  the 
various  modifications  which  they  present  may  be  postponed. 

Excretory  organs  in  the  form  of  a  pair  of  uephridia  are 
present,  each  nephridium  consisting  of  a  tube  which  opens  at 
one  extremity  into  the  mantle-cavity,  while  at  the  other  it 
communicates^  with  the  cavity  of  the  pericardium,  which,  as 
has  been  seen,  is  a  portion  of  the  coelom.  The  relationships 
of  these  structures  are  therefore  the  same  as  those  of  the 
nephridia  of  the  Annelids,  and,  as  in  those  forms,  they  receive 
a  rich  supply  of  blood,  most  of  the  venous  blood  returning  from 
the  tissues  passing  through  their  walls  on  its  way  to  the 
branchiae.  The  reproductive  organs  are  unpaired  in  the 
majority  of  forms  and  in  some  cases  come  into  relation  with 
the  nephridia,  which  serve  as  reproductive  ducts.  More 
usually,  however,  they  open  directly  to  the  exterior,  a  con- 
dition which  is  probably  a  secondary  one.  The  majority  of 
the  Mollusca  are   bisexual,  but   hermaphroditism  is  by  no 


284 


IN  VERTEBRA  TE  MORPHOLOG  7. 


I-, 


f.% 


means  uncommon,  the  single  reprodu«itive  gland  producing 
both  ova  and  spermatozoa  and  being  therefore  an  ovo-testis.. 
Accessory  structures  are  frequently  added  to  the  essential 
parts  of  the  reproductive  apparatus,  such,  for  instance,  as  al- 
buminiparous  glands,  introraittent  organs,  spermatophore- 
sacs,  etc.,  so  that  a  relatively  complicated  arrangement  may 
occur. 

I.  Class  AMPHlNEFilA. 

The  Amphineura  are  Mollusca  iu  which  the  primitive  bi- 
lateral symmetry  is  fully  retailed  and  which  seem  to  approach 
most  nearly  to  what  may  be  considered  the  primitive  Moliuscau 
condition.  All  the  known  members  of  the  jjroup  are  marine 
in  habitat  and  are  more  cr  less  elongated  forms  in  which  the 
elongat:  )n  of  the  ventral  surface  or  foot  is  accompanied  by  a 
corresponding  elongation  of  the  visceral  complex,  which  ac- 
cordingly is  not  elevated  at  right  angles  to  the  long  axis  of 
the  foot  to  form  a  visceral  dome.  In  a  general  way,  therefore,  in 
the  form  of  their  body  the  Amphineura  may  be  compared  to  the 
Platyhelminths,  especially  to  such  forms,  sometimes  flattened, 
sometimes  more  or  less  cyliudrical  and  elongated,  as  are  found 
among  the  Folyclad  Turballaria.  The  mouth  and  anus  are  situ- 
ated at  the  extremities  of  the  body,  and  to  either  side  of  the  anus 
are  situated  the  one  or  more  pairs  of  plumelike  brauchiie  and  the 
openings  of  the  single  pair  of  nephridia.  The  shell  may  con- 
sist either  of  a  number  of  scattered  calcareous  spicules  im- 
bedded in  or  projecting  from  a  thick  cuticle,  or  else  may  take 
the  form  of  a  number  of  plates  arranged  in  a  )  )ugitudinul 
series  upon  the  dorsal  surface  of  the  body,  and  as  a  rule  the 
miMitlo-f^ld  is  but  slightly  developed  and  ma}'  be  in  son^e  forms 
almost  rudimentary.  The  foot,  too,  wJiich  is  so  characteristic 
for  the  ISiollusca,  may  iu  soDie  forms  be  practically  un- 
developed, but  in  other  forms  is  a  broad  flat  mu8cuh\r  sunace, 
showing  no  differentiation  into  special  regions  such  as  are 
found  in  the  higher  Mollusca. 

Little  need  be  said  iiere  as  to  tlie  internal  organs  except  to 
emphasize  the  fact  that  both  the  heart  and  the  nephridia  have 
a  perfectly  bilateral  arrangement.  The  nervous  system  is 
characterized  by  the  absence  of  a  deiiuite  agrregatiou  of  the 


TYPE  M0LLU8CA. 


285 


nerve-cells  into  concrete  ganglia ;  they  are  scattered  along  the 
lougitucliual  nerve-cords,  of  which  there  are  two  pairs,  i.e.,  the 
pleuro-viscer,",!  cords,  which  run  along  the  lateral  portions  of 
the  bod}',  and  the  pedal  cords,  which  are  situated  jQore 
ventrally  and  whi.'ih,  as  well  as  the  pleuro-visceral,  are  fre- 
quently united  by  cross-commissures  which  suggest  an  imper- 
fect metamerism.  In  front  tiiese  cor<^3  unite  together  to  form 
the  civeumoesophageal  ring  in  which  the  ganglion-cells  are 
someyd^at  more  numerous  than  elsewhere,  without,  however, 
forming  distinct  ganglia.  Sense-organs  are  but  slightly  de- 
veloped throughout  the  group,  which  is  divisible  into  two  well- 
marked  orders. 


Fig.    126. — Neomenia  ca- 
rinata  (after  Nansen). 

ct  —  ctcnidium. 

m  ~  mouth. 

eg  ~  v'jiitriil  groove. 


1.  Order  Solenogastres. 

The  members  of  this  order  are  for  the  most  part  elongated 
worm-like  animals,  though  some  forms  are  short  (JTig.  126) 
and  more  nearly  approach  the  typical 
Molluscan  lorm.  The  exterior  of  the 
body  is  covered  by  an  exceptionally 
thick  cuticle  traversed  by  bauds  of 
cells  extending  into  it  from  the  ecto- 
dermal layer  of  the  body  and  termina- 
ting in  cui)-shaped  groups  of  cells 
whicli  secrete  the  calcareous  spicules 
which  are  scattered  through  the  cuti- 
cle {Proneomenia)  or  may  project  upon 

its  surface  {Chtvioderma),  and  which  are  the  sole  repre- 
sentatives of  the  shell  of  the  higher  MoHusca.  Upon  the 
ventral  surface  of  the  body  is  a  Inngitudiual  furrow  (Fig.  12(5, 
vg)  at  the  bottom  of  which  lies  tiie  but  sliglitly  developed 
foot,  represented  by  a  small  ciliated  l(>ngitudinal  ridge,  which  in 
Chvtoderma  \\m\\  be  (piite  undeveloped,  tlie  furrow  being  in  tliis 
form  also  barely  indicated  or  entirely  absent.  The  lips  of  the 
furrow  which  enclose  the  foot  probably  represent  the  mantle- 
folds  of  higher  forms,  here  very  nnu^h  reduced,  though  more 
extensively  developed  at  the  posterior  end  of  the  body,  where 
they  projoet  to  frirsn  a  fnnutl'liko  structiiro  (Fig.  127)  whose 
cavity — the    cloaca — receives    the   openings  of  the  digestivo 


286 


INVEliTEBltATE  MOIiPJIOLOOY. 


Fig.    127.  —  DiAOKAM    of   Au- 

KANOEMENT     OF     ()H(JANS     AT 

lIiNU    End    of     Glurtcth'rma 
(after  Hubhboht  from  I^ankebtkb). 

ct  —  ctenidiuin. 
n  —  nepluidium. 
0  =  ovary. 
p  =  periciirdiuni. 
r  =  rectum. 


tract  (r)  aud  the  uephridia  ^n)  and  contains  the  branchiso  {ct). 
These  hist  are  either  a  single  pair  of  structures  each  consisting 

of  a  central  axis  with  pinnately- 
arrauged  lateral  appendages  or  in 
some  cases  are  represented  by 
bunches  of  ciliated  filaments. 

The  ectoderm  rests  upon  a 
layer  of  muscular  tissue  in  which 
both  circular  and  longitudinal 
layers  can  be  distinguished,  and 
numerous  bands  of  transverse 
libi'es,  in  some  cases  arranged  to 
form  septa  placed  at  regular 
intervals,  traverse  the  body- 
cavity.  A  fairly-capacious  peri- 
cardium is  present,  lying  dorsally 
to  the  i«)sterior  porticm  of  the  digestive  tract  and  into  its 
upper  portion  the  heart  i)roject8  slightly,  not  being,  however, 
completely  enclosed  by  the  pericardium.  No  auricles  seem 
to  be  developed,  nor  are  any  definite  blood-vessels  present, 
the  circulation  being  throughout  lacunar. 

Tliis  condition  of  the  heart  in  relation  to  the  pericardium  is  interesting 
as  sliowing  its  original  independence  of  that  portion  of  the  body-cavity. 
Its  enclosure  in  the  pericardium  in  the  higher  Moilusca  is  a  secondary  con- 
dition, the  heart  and  its  cavity  belonging  to  the  schizoccelic  structures 
rather  than  to  {\w,  so-called  enteroca>lic  i)ericardium.  This  agrees  perfectly 
with  tiio  relationships  of  the  blood  vascular  system  of  the  Nemerteans  and 
Annelids.     (See  pp.  105  and  381.) 

The  mouth  is  a  longitudinal  slit  upon  the  ventral  surface 
«'f  the  body  aud  opens  into  u  pharynx  i)rovidod  usually  wHh  a 
iMchila  and  with  salivary  ghinds,  though  both  these  structures 
ure  absent  in  Neomeuw.  Tlie  intestine  pursues  a  straight 
course  towards  the  anal  opening,  being,  however,  in  some 
forms  i)ouched,  owing  to  its  constriction  at  more  or  less  regu- 
lar and  close  intervals  by  muscular  transverse  se'pta.  The 
walls  of  the  pouches  thus  formed  are  glandular  and  represent 
the  digestive  gland  of  other  Moilusca,  though  in  Olia'ttHfcrmn 
there  i«  a  simple  ontgrowth  of  t!io  digestive  tract  wiiich  rep- 
resents  it  more  perfectly. 


TYPE  MOLLUSC  A. 


287 


The  nervous  system  varies  iu  the  details  of  its  arrange- 
uient  iu  the  different  species,  but  is  characterized  'u  general 
by  a  tendency  to  form  ganglia,  although  nerve-cells  are  scat- 
tered along  the  nerve-coru.'  throughout  their  entire  length. 
In  rroneomenia  there  is  present  a  well-developed  and  closely- 
approximated  pair  of  cerebral  ganglia  from  which  arise  the 
pleuro-visceral  cords  which  extend  backward  along  the  sides 
of  the  body  and  possess  a  number  of  ganglionic  swellings 
near  their  posterior  extremity.  Two  nerve-rings  surround  the 
oesophagus:  (1)  the  cerebro-pedal  connectives,  which  end 
below  in  the  pedal  ganglia,  from  which  two  pedal  cords  extend 
backward  along  the  foot,  in  some  forms  {Dondersia)  connected 
at  regular  intervals  by  transverse  commissures  in  an  almost 
nietameric  manner,  ganglionic  enlargements  of  the  cords  being 
developed  iu  connection  with  the  commissures ;  and  (2)  the 
<;erebro-buccal  connectives,  which  pass  to  two  buccal  ganglia 
lying  below  the  pharynx.  Special  sense-organs  have  not  yet 
been  discovered  in  the  Solenogastres. 

The  nephridia  consist  of  a  pair  of  tubes  which  communi- 
cate  internally  with  the  pericardial  cavity  and,  bending  around 


FiQ.  188.— DiAOHAMMATic  LONGITUDINAL  SKCTIO^  OF  Chiton  (after  Hallkb) 
e  =  perivisceral  ca'lom.  n  =  iiervf. 


h  =  heart. 
m  —  iiiotitli. 


1-8 


p  =  |)eric('.r(lliiin. 
ro  —  reproductive  orgiin. 
sUell-|)lates. 


the  posterior  ])art  of  the  digestive  tract,  unite  to  o])en  into  the 
cloaca  ventral  to  the  anus  by  a  common  n-itice.  The  walls  of 
the  tubes  are  glandular  and  jnobabjy,  therefore,  excretory  iu 
function,  but   the   nephridia  also  serve  as  the  ducts  for  the 

"    i '--.i.-  !iir-.i       IT  nil  luc  cvs^trptiv/ii  !>i   r^rirrtuficrriKl  the 

tJoleuogastre ;   are    hermaphrodite,    the   single   reproductive 


288 


INVERTEBRATE  MORPHOLOGY. 


l,^ 


>  , 


!H 


gland  producing  both  ova  and  testes.  This  hermaphrodite 
gland  is  a  hollow  sac  divided  into  two  principal  compart- 
ments by  a  longitudinal  partition  and  lies  above  the  digestive 
tract.  It  is  a  hollow  structure  (Fig.  128,  ro),  the  reproductive 
elements  developing  from  the  cells  lining  its  walls  and  pass- 
ing from  its  cavity  into  that  of  the  pericardium  (p),  with 
which  the  reproductive  sacs  communicate.  They  are  in  fact 
simply  prolongations  of  the  pericardial  body-cavity,  and  the 
epithelium  lining  them  is  continuous  with  that  of  the  pericar- 
dium. From  the  pericardial  cavity  the  ova  and  spermatozoa 
pass  to  the  exterior  by  the  nephridia. 

The  Solenogastres  are  especially  interesting  on  account  of  the  many 
structural  peculiarities  of  a  primitive  character  which  they  present  and  in 
consequence  of  which  they  have  been  regarded  as  representatives  of  ances- 
tral Molluscan  forms.  By  others,  however,  this  important  position-  is 
denied  them  on  the  ground  that  many  of  their  peculiarities  are  due  to 
degeneration  produced  in  accordance  with  their  life  in  the  mud  at  the  bot- 
tom of  the  ocean.  The  absence  of  a  shell,  the  reduction  of  the  mantle- 
lobfp,  foot,  and  radula  may  with  plausibility  be  accounted  for  in  this 
manner,  but  there  are  other  peculiarities  that  are  certainly  primitive 
which  are  not  thus  explicable.  The  relation  of  the  heart  to  the  pericardium 
is  one  of  these,  and  others  are  the  communication  of  the  hermaphrodite 
gland  with  the  pericardium,  and  the  functioning  of  the  nophridia  as  ducts 
for  the  reproductive  organs.  The  Solenogastres  are  unquestionably  primi- 
tive MoUusca;  the  only  question  which  is  yet  to  be  settled  is  to  what  extent, 
if  any,  degeneration  is  responsible  for  their  external  peculiarities,  such  as 
the  absence  of  a  shell,  the  reduction  of  the  mantle-lobes  and  of  the  foot. 
It  must  be  noted  in  this  connection  that  one  form  belonging  to  tlie  genus 
Pondevfiia  has  been  described  as  passing  through  in  its  development  a 
stage  in  which  indicatiojis  of  a  shell  consisting  of  several  plates  and  simi- 
lar to  that  of  the  Polyplacophora  was  present,  a  condition  wliicli  would 
seem  to  indicate  the  derivation  of  the  members  of  this  group  from  forms 
provided  with  a  distinct  shell. 

2.  Order  Polyplacophora. 

Tlie  Polyplacophora,  like  the  preceding  order,  contains 
only  marine  forms.  For  the  most  part  they  are  somewhat  fl.it- 
toned  animals  with  a  rather  broad  foot  occupying  the  ventral 
surface,  while  from  the  sides  of  the  body  a  sliglit  fold,  the 
mantle-fold,  uroiects.  In  one  crenus,  ChitoneRus.  tlie  form  of 
the  body  is  more  cylindrical  and  tlie  foot  is  rather  narrow 


TYPE  MOLLUSC  A. 


28& 


Fig.  129.— C/«Bto- 
pleura  apiculata. 


and  situated,  as  in  the  Solenogastres,  at  the  bottom  of  a 
median  ventral  furrow,  the  lips  of  which  correspond  to  the 
more  dorsally  situated  mantle-folds  of  such  forms  as  Chiton, 
Trachydermon  (Fig.  129),  etc.  In  all  cases,  in  the  groove  be- 
tween the  mantle-folds  and  the  foot  a  number  of  gills,  pinnate 
processes  of  the  body-wall,  are  to  be  found,  in  some  cases 
occurring  at  definite  intervals  along  the  entire  side  of  the 
body,  in  others  {Chitonellus)  limited  to  the  posterior  part  only. 

One  of  the  most  characteristic  features  of  the 
Polyplacophora  is,  however,  the  shell,  which 
consists  of  eight  calcareous  plates  arranged  in 
a  longitudiral  series  along  the  dorsal  surface 
of  the  body  so  that  the  posterior  border  of  one 
overlaps  the  anterior  border  of  the  other. 
The  series  covers  only  the  median  portion  of 
the  surface,  the  more  peripheral  portions  and 
the  outer  surface  of  the  mantle-lobes  possess- 
ing a  large  number  of  scattered  spicules, 
plates  or  granules  imbedded  in  their  wall. 

The  body-wall  has  not  so  definite  an  arrangement  of  the 
muscle-fibres  lying  below  the  ectoderm  as  is  the  case  in  the 
Solenogastres,  but,  on  the  other  hand,  the  body-cavity  is  well 
developed.  Indeed  the  schizocoelic  lacunae  play  a  rather  sub- 
ordinate part  in  the  Chitonidre,  as  the  order  is  sometimes 
termed,  the  enterocoelic  cavity  (Fig.  128)  being  very  large  and 
divisible  into  three  usually  separated  parts  united  by  bands, 
which  indicate  the  original  continuity.  One  of  the  parts  (c) 
surrounds  the  intestine  and  the  digestive  gland  ;  another,  lying 
iiitlier  towards  the  anterior  end  of  the  dorsal  portion  of  the 
body,  contains  the  reproductive  cells  (ro);  while  the  third  part 
ip),  lying  dorsally  and  posteriorly,  is  the  so  called  pericar- 
<liuin. 

The  two  auricles  of  the  heart  are  elongated  tubes  which 
communicate  with  the  single  ventricle  by  one  or  several  pairs 
of  o])enings  an.'  Iso  unite  together  posteriorly,  the  ventricle, 
also  an  elongated  tube,  sometimes  again  communicating  with 
this   united   portion.     Anteriorly  the  ventricle   is  continued 

into  n.  siliorf.  nr^j'fii    fviirn   v'l>'f»l!    il>o   ]»1 1 +-    il        1 

""  • - ''•  >Ti.jLii  liit  Ejjwwvi  piiaaus  U)  tiie  iacnnar 

Hl)ace8  of  the  schizoccjel.     Two  vessels  w 


distinct  walls  r 


un 


290 


mVERTEBRA  TE   MORPHOLOO  T. 


4 


'a 


longitudiually  in  the  foot,  aud  presumably  receive  the  blood 
which  they  contain  more  or  less  directly  from  the  aorta  aud 
distribute  it  to  the  lacunar  spaces  of  the  foot. 

The  mouth  lies  on  the  ventral  surface,  in  front  of  the 
anterior  end  of  the  foot,  and  leads  into  a  pharynx  provided 
with  a  well-developed  radula  characterized  by  a  somewhat 
complex  arrangement  of  the  teeth.  Into  the  oesophagus 
a  pair  of  glands  opens  in  Chiton  whose  secretion  contains  an 
amylolytic  ferment,  and  in  addition  a  pair  of  small  glands 
open  into  the  mouth-cavity.  The  oesophagus  communicates 
with  a  sac-like  stomach,  into  which  open  the  ducts  of  the 
paired  digestive  gland,  and  the  intestine,  being  considerably 
longer  than  the  body,  is  thrown  into  numerous  coils,  and 
terminates  by  a  short  rectum  which  opens  at  the  posterior 
extremity  of  the  body. 

The  nervous  system  is  characterized  by  the  diffuse 
arrangement  of  the  nerve-cells,  no  well-defined  ganglia  oc- 
curring on  the  principal  nerve-cords.  These  consist  of  a 
strong  circumoesophageal  ring  (Fig.  130),  the  upper  part  of 
which  gives  off  numerous  nerves  and  evidently  corresponds 
to  the  cerebral  ganglia  of  other  Mollusca,  while  the  lower 
part,  corresponding  to  the  pedal  ganglia,  gives  rise  to  two 
nerve-cords  (pc),  the  pedal  nerves,  which  pursue  a  parallel 
course  throughout  the  foot,  giving  off  a  number  of  nerves 
laterally  and  being  connected  by  a  number  of  somewhat  irreg- 
ularly arranged  transverse  commissures,  which  almost  suggest 
a  metameric  arrangement.  From  the  sides  of  the  circum- 
oesophageal ring  two  other  strong  nerves,  the  pleuro-visceral 
nerve-cords,  arise  and  pass  backwards  along  the  sides  of  the 
body,  uniting  with  each  other  posteriorly  above  the  terminal 
portion  of  the  digestive  tract.  These  cords  {ji),  like  the  cir- 
cumuusophageal  ring,  present  no  distinct  ganglionic  enlarge- 
ments, but  contain  the  elements  of  the  pleural,  visceral,  and 
parietal  ganglia,  sending  off  numerous  nerves  to  the  brauchias 
tlie  mantle,  aud  probably  also  to  the  heart  and  nephridia. 

In  addition  to  these  principal  nerve-cords  others  of  smaller 
size  also  arise  from  the  circumtwsophageal  ring.     One  pair  of 


J  - 


beneath  the  buccal  mass  and  send  nerves  to  the  oesophagus 


le  blood 
orta  and 

t  of  the 
provided 
omewliat 
upliagus 
itaius  au 
11  glands 
mnicates 
s  of  the 
dderably 
oils,  and 
posterior 

I  diffuse 
nglia  oc- 
sist  of  a 
c  part  of 
responds 
he  lower 
B  to  two 

parallel 
f  nerves 
lat  irreg- 
t  suggest 

circum- 
)- visceral 
3S  of  the 
terminal 
B  the  cir- 
enlarge- 
eral,  and 
»ranehias 
lidia. 
f  smaller 
e  pair  of 
ia.  Ivi!!!/ 
(ophagus 


TYPE  MOLLUSCA. 


29  L 


while  another  pair  pass  to  a  pair  of  ganglia  lying  below  the 
radula  and  in  intimate  connection  with  a  peculiar  subradular 
organ,  probably  sensory,  lying  in  this  region. 


Fig.  130.— Diagram  of  Neuvous  and  Excretohy  Systems  of  Chiton  sieulus 

(uoiiibiiiation  of  two  figures  by  Haller). 
an  —  iimis.  no  =  uephridial  orifice. 

Br  =  ctenidia.  oe  =  ccsophagus. 

go  =  genital  orifice.  pc  =  jiedal  nerve  cord, 

ft  =  uepliridiiiin.  pi  =  pleural  nerve-cord. 

As  regards  sense-organs,  in  addition  to  this  subradular 
organ  whose  function  is  entirely  problematical,  ridges  of 
sensory  epithelium  exist  along  the  sides  of  the  body  in  the 
lu.intle-cavity.  One  such  ridge  runs  along  the  inner  wall  ot 
tiie  mantle-fold,  while  the  other  is  found  at  the  bottom  of 
the  mantle-cavity  passing  over  the  bases  of  the  branchial 
l)hinie8and  sending  a  short  prolongation  outwards  upon  each 

IJ—  •"     -^ -^-    •-•  vf  •*•    i'*s  •  •  ■■ '    ....... ^     ^...- '-  * -t  I  ■_  !:75j'^„'iii.t     TTiLii    tiitr 

osphradia  of  other  Mollusca. 


mm 


11       I 


292 


INVERTEBRA TE  MORPHOLOG  7. 


A  much  more  peculiar  series  of  organs,  found,  however,  in 
their  perfect  form  only  in  certain  species,  is  developed  in 
connection  with  the  shell  of  the  Chitonidae.  They  consist  of 
club-shaped  structures  contained  in  pores  which  traverse  the 
shell-plates  and  possess  a  definite  arrangement,  being  ar- 
ranged in  groups  of  larger  and  smaller  organs  {megalcesthetes 
and  micrcesthetes).  Each  group  is  in  connection  with  a  num- 
ber of  large  glandlike  cells,  which  terminate  in  the  megal- 
iesthete,  covered  externally  by  a  cup-shaped  layer  of  chitiu, 
and  from  this  cell-mass  more  or  less  numerous  branches 
arise,  the  micrsBsthetes,  which  terminate  in  club-shaped 
swellings  likewise  covered  by  a  chitinous  layer.  Below  the 
group  of  cells  is  in  connection  with  fibrils  which  unite  to 
form  a  nerve  probably  passing  to  the  pleuro-visoeral  nerve- 
cords,  and  it  thus  seems  tolerably  certain  that  these  struc- 
tures are  sensory  and  perhaps  tactile  in  function.  In  some 
species  the  megahesthetes  become  modified  into  eyes  consist- 
ing of  an  external  convex  chitinous  cap,  the  cornea,  below 
which  is  a  lens  and  below  this  a  layer  of  retina-cells  con- 
nected  with  nerve-fibrils  and  surrounded  by  a  cup  of  pig. 
ment-cells.  No  eyes  other  than  these  occur  in  the  Polypla- 
cophora,  nor  are  tactile  tentacles  or  otocysts,  of  such  fre- 
quent occurrence  in  other  Moliusca,  found. 

The  nephridia  (Fig.  130,  n)  are  paired,  one  lying  on  each 
side  of  the  body  and  consisting  of  a  long  tube  giving  rise  to 
numerous  dendritic  branches.  Posteriorly  the  tube  branches, 
one  of  the  branches  opening  into  the  mantle-cavity  in  its 
posterior  part,  while  the  other  communicates  with  the  peri- 
cardial  portion  of  the  enterocoel.  In  function  these  organs 
of  the  Chitonidie  difiers  from  the  corresponding  ones  of  the 
Solenogastres  in  being  excretory  only  and  in  not  serving 
as  ducts  for  the  reproductive  elements.  These  are  developed 
in  a  portion  of  the  enteroccjel  which  lies  anteriorly  to  the 
pericardium  and  make  their  way  to  the  mantle-cavity  and  so 
to  the  exterior  by  special  ducts  arising  one  on  each  side  frotn 
near  the  posterior  part  of  the  reproductive  enterocoel  and 
ending  (go)  on  the  sides  of  the  body  slightly  in  front  of  tho 
openings  of  the  nephridia  (no).  The  Polyplacophora  are  with- 
out exception  bisexual. 


TYPE  MOLLUSCA. 


293 


The  structural  peculiarities  of  the  Polyplacopliora  point  strongly  to 
their  i)rimitive  chantcter,  though  in  many  respects  they  are  less  primitive 
than  the  Soleiiogastres.  Thus  they  possess  special  reproductive  ducts,  in  all 
probability  a  secondary  acquisition,  and  furthermore  the  reproductive  and 
pericardial  moieties  of  the  enterocoel  no  longer  communicate  freely.  If 
tlie  ISolenogastres  have  been  derived  from  forms  with  Chiton-like  shells 
(see  p.  288),  then  it  must  be  supposed  that  the  two  groups  r;;present  di- 
verging lines  of  development  from  a  common  ancestor  whose  character- 
istics have  been  partly  retained  in  the  one  group  and  partly  in  the  other. 


II.  Class  Gasteropoda. 

The  Gasteropoda  form  a  very  complex  group,  the  various 
members  differing  so  much  in  the  details  of  their  organiza- 
tion that  it  is  difficult  to  give  a  general  description  which 
will  apply  to  all  the  forms.  Certain  features  may,  how- 
ever, be  considered  typical  of  the  class,  and  these  may  be 
mentioned  here,  reserving  notice  of  the  more  important  varia- 
tions until  the  various  subdivisions  are  being  considered. 

One  of  the  most  characteristic  features  is  the  occurrence  of 
what  may  be  termed  the  '•  visceral  hump  "  whose  presence  is 
responsible  for  many  of  the  peculiarities  of  Gasteropod  struc- 
ture. It  consists  of  an  elevation  into  a  dome-like  structure 
of  the  dorsal  region  of  the  body,  the  digestive  tract  and 
gland  being  contained  within  the  elevation.  The  mantle 
arises  as  a  circular  fold  surrounding  the  hump,  but  usually  is 
more  liighly  developed,  and  therefore  encloses  a  deeper 
cavity,  upon  the  right  side  or  anterior  surface  of  the  hump, 
and  in  the  cavity  so  arranged  lie  the  structures  which  usually 
are  associated  with  the  mantle-cavity,  namely,  the  braucliisB 
and  the  openings  of  the  digestive  tube  and  of  the  ne2)hridia. 
There  is  thus  a  very  decided  asymmetry  in  most  Gastero])ods, 
usually  emphasized  by  the  visceral  humj)  being  coiled  into  a 
spiral,  a  coiling  which  is  shared  by  the  shell,  usually  present 
and  consisting  of  a  single  tubular  structure  surrounding  the 
visceral  hump,  but  usually  sufficiently  ample  to  permit  of  the 
retraction  within  it  of  the  rest  of  the  body. 

In  a  number  of  forms  the  visceral  hump  may  be  very 
i)^^^/>]}  vfi|(|i|f>orl  and  with  this  reduction  there  is  feuerallv  con- 
comitant a  redu.^^ion  of  the  shell,  but  such  conditions  are 


^f  '11 


i 


294 


INVERTEBRATE  MORPHOLOGY. 


pliiinly  secondary  iuasmucli  as  the  primitive  asymmetry  is 
iudicated  in  certain  of  the  organs  in  all  cases.  In  order  to 
understand  the  exact  nature  of  this  asymmetry  it  will  be  nec- 
essary to  consider  what  may  have  been  the  original  form  of 
the  Gasteropoda.  Judging  from  what  is  known  of  the  Amphi- 
neura,  it  may  be  supposed  that  in  the  primitive  Gasteropod 
(Fig.  131,  A)  the  anus  (a)  was  terminal  and  opened  into  a 
mantle-cavity,  the  mantle  being,  except  posteriorly,  only  a 
slight  fold.  In  this  mantle-cavity  there  was  present  also  a 
single  pair  of  branchial  plumes  (c/),  and  into  it  the  two 
nephridia  opened  («),  passing  frftm  the  posteriorly-situated 
pericardium  which  contained  the  heart  provided  with  two 
auricles. 

It  may  be  imagined  now  that  in  such  a  form  the  visceral 
hump  enclosed  by  a  dome-like  shell  became  elevated  to  such 
an  extent  that  it  could  no  longer  be  retained  in  an  erect  posi- 
tion, but  fell  over  to  one  side — it  may  be  supposed  the  left 
side.     The  result  of  this  would  be  an  interference  with  the 
development  of  the  mantle-cavity  towards  the  left  side,  and 
a  prevention  of  the  pf^rfect  growth  of  the  left  branchia  and  of 
the  proper  functioning  of  the  left  nephridium.     There  would 
be  a  tendency  then  for  the  mantle-cavity,  and  with  it  the  anus 
and  indeed  the  entire  posterior  region  of  the  body  with  the 
heart  and  nephridia,  to  be  pushed  over  towards  the  right  side 
(Fig.  131,  B),  and  this  process  might  in  some  cases  be  con- 
tinued until  the  mantle-cavity  and  the  organs  associated  with 
it  had  been  pushed  round  through  180°  (Fig.  131,  C\  D)  and 
had  come  to  lie  apparently  in  front  of  the  visceral  hump  (Z>). 
The  anus  in  sucli  a  case  would  open  into  the  mantle-cavity  in 
the  mid  line,  dorsal  to  the  mouth,  and  what  was  originally  the 
right  branchia  would  lie  upon  the  left  side  of  the  body ;  the 
digestive  tube,  which  may  originally  have  been  practically  a 
straight  tube,  would  now  be  bent  upon  itself,  and  furthermore 
the  original  right  parietal  nerve-ganglion  would  have  passed 
over  to  the  left  side  of  the  body  and  the  original  left  ganglion 
to  the  right  side,  a  crossing  of  the  pleuro-parietal  connectives 
{vc)  being  thus  brought  about. 

The   original   pressure   of  the   shell   upon   the  left   half 
of  the  mantle-cavity  would,  however,  as  pointed   out,  have 


TYPE  MOLLUSCA. 


295 


tended  to  produce  a  retardation  in  the  growth  or  even  the 
complete  abortion  of  the  organs  lying  in  that  region.  Accord- 
ingly the  original  left  uephridiuni  is  in  many  Gasteropods  com- 
pletely  suppressed  as  well  as  the  original  left  branchia,  and 
in  accordance  with  the  disappearance  of  this  latter  structure 


Fig.  131.— Diagrams  to  illustrate  the  Rotation  of  the  Mantle-c  wity 
AND  ITS  Organs  in  a  GASTEitorou  (after  flguifs  by  Butschli  and  Lakg  fiouL 
KoRscHELT  and  Heider). 

«  —  Hims.  m  =  mouth. 

ao  =  aortu.  n  =  uephiidial  pore. 

ct  -  ctenidhmi.  peg  =  pedal  ganglion. 

eg  =  cerebral  ganglion.  p/g  =  pleural  ganglion. 

vc  =  visceral  connective. 

there  is  a  disappearance  also  of  the  left  auricle  of  the  heart 
which  receives  blood  from  it. 

The  visceral  hump  does  not,  however,  retain  its  original 
conical  form,  but,  owing  perhaps  to  unequal  pressure,  grows 
more  rapidly  upon  one  surface,  the  anterior,  and  so  becomes 
coiled  into  a  right-handed  spiral,  the  shell  covering  the 
hump  naturally  assuming  a  similar  form.     In  the  majority  of 


296 


IN VERTEDUATE  MOltPnOLOO Y. 


'f 


% 


Gasteropods  consequeutly  a,  shell  coiled  in  a  right-baiuled 
spiral  occurs,  but  this  rule  has  uot  a  few  exceptions.  Where 
the  shell  forms  a  left-handed  spiral  it  is  to  be  explained  by 
supposing  that  in  such  cases  the  visceral  hump  tended  towards 
the  right  side  of  the  body  rather  than  the  left,  and  this  is 
confirmed  by  the  fact  that  in  most  left-handed  forms  it  ia  the 
left  branchia  and  nephridium  that  have  persisted. 

It  must  be  pointed  out,  however,  that  the  extent  to  which 
the  rotation  of  the  mantle-cavity,  the  abortion  of  the  orrjans 
of  either  the  left  or  right  side  of  the  body,  and  the  crossing 
of  the  pleuro- parietal  nerve-cords  has  been  carried  varies  m 
different  forms.  In  some  the  rotation  has  been  curried  so  far 
that  the  original  right  branchia,  etc.,  has  passed  the  median 
line  in  front  so  as  to  lie  on  the  left  side  of  the  bodj',  and  in 
such  cases  the  crossing  of  the  nerve-cords  (chiastoneurism)  is 
completed.  Many  forms,  however,  stop  short  of  this,  and 
numerous  gradations  are  to  be  found.  The  rotation,  however, 
is  present  in  all  forms  to  some  extent  and  forms  a  character- 
istic feature  of  Gasteropod  morphology. 

The  anterior  portion  of  the  body  (Fig.  132)  is  usually  well 
marked  off"  by  a  more  or  less  distinct  constriction  or  neck,  and 
consequently  it  is  possible  in  the  Gasteropods  to  speak  of  a 
head  in  contradistinction  to  the  trunk  rb„ion  of  the  bod}' ;  in- 
deed so  prevalent  is  this  character  that  the  term  Cephalo- 
phora  has  been  applied  to  the  group.  Tentacles,  either  one  or 
two  pairs,  are  borne  by  the  head,  and  furthermore  eyes  are 
usually  present  upon  it  either  at  the  bases  of  one  of  the  pairs 
of  tentacles  or  else  borne  at  the  tips  of  these  structures. 

The  foot  is  generally  well  dp  f  lo^ed  and  usually  has  a  flat 
creeping  sole.  It  undergoes  muDv  i>vodificatjou'',  however, 
sometimes  becoming  more  kee'  In^f^  or  bocoming  differentiated 
into  three  regions  differing  in  form,  the  propodium,  mesopo- 
dium,  and  metapodium,  the  last-named  portion  frequently 
secreting  a  chitinous  plate,  the  operculum  (Fig.  132,  op),  which 
serves  to  close  the  mouth  of  the  shell  when  the  animal  is 
withdrawn  within  it.  In  addition  to  these  portions  an  epipo- 
dium  is  frequently  highly  developed,  consisting  in  its  primi- 
tive form  of  a  fold  arising  from  the  sides  of  the  foot  where  it 
passes  into  the  body-wall.     In  many  cases,  however,  it  loses 


TYPE  M0LLU8CA. 


297 


this  simple  form,  its  margin  becomiug  fringed  or  tentaculate, 
or  elst  it  may  be  reduced  to  one  or  more  separate  lobes  or 
tentacular  ])roce88es  on  either  side  of  the  body.  Openiu<^ 
upon  the  surface  of  the  foot  is  frequently  to  be  found  a  so" 
called  "foot-gland  "  which  secretes  a  sticky  raucous  fluid  and 
is  comparable  to  the  byssus-gland  of  the  Pelecypoda  {q.  v.). 


Fi(i.  132. — Buecihum  undatum. 
op  =  opcicuUiiii.  8i  =  siplio. 

The  respiratory  organs  (Fig.  133,  d)  consist  in  typical  cases 
of  a  single  pair  of  pinnate  branchial  plumes  lying  in  the 
mantle-cavity,  but,  as  has  already  been  mentioned  in  conuec- 
tion  with  the  rotation  of  that  cavity,  one  of  these  structures  is 
very  frequently  aborted.  Other  changes,  however,  also  occur, 
such,  for  example,  as  the  fusion  of  the  central  axis  of  the 
branchial  plume  throughout  its  entire  length  to  the  inner 
surface  of  the  mantle  {Haliotis),  or  the  disappearance  of  the 
pinntB  from  one  side  of  the  plume  in  connection  with  such  a 
fusion  {Sycotyptis,  Fig.  133).  In  some  forms  accessory  bran- 
chijG  may  be  produced  as  folds  of  the  mantle,  richly  supplied 
with  blood,  and  their  development  may  be  carried  to  such  an 
extent  that  they  may  entirely  supplant  the  branchiae  proper 
(Patella).  From  such  a  condition  as  this  a  passage  is  not  dif- 
Hcult  to  such  a  condition  as  is  found  in  the  air-breathing  Gas- 
teropods  (Pulmonata)  in  which  the  entire  inner  surface  of  the 
mantle  serves  a  respiratory  purpose,  an  interchange  of  gases 
tidiing  place  between  the  air  contained  in  the  mantle-cavity 
and  the  blood  which  is  richly  supplied  to  the  mantle. 

The  musculature  of  the  body-wall  does  not  as  a  rule  pre- 
sent the  Annelidan  arrangement  in  layers,  as  in  some  Amphi- 
neura,  but  usually  are  irregularly  arranged  as  dorso-ventral 
and  oblique  bands  traversing  the  schizocoel.    Special  muscles, 


t4 


298 


INVfiliTEBltA TE  MOliPHOLOGT. 


however,  are  developed  in  many  forms,  the  most  important 
beiu^  those  connected  with  the  foot  and  servinj^  for  h)comotiou, 
r«>tractor  muscles  in  connection  with  the  head,  proboscis,  and 
tentacles,  and  the  spind'e-niuscle,  which  has  a  general  vertical 
direction  running  along  the  right  side  of  the  visceral  hump 
from  its  insertion  into  the  shell  to  the -foot  in  whose  wall  its 
fibres  spread  out,  intolacing  as  it  were  with  the  horizontal 
and  trans  erse  muscles  there  developed  ;  it  serves  to  retract 
the  entire  animal  within  the  .ihell,  and  its  development  is 
naturally  in  proportion  t>  that  of  the  shell,  those  forms  in 
wh'ch  the  shell  is  rudimentary  or  absent  frequently  lacking  it. 

The  enteroc<i(lic  portion  of  the  co'hjm  is  much  reduced 
in  comparison  with  what  occurs  in  the  Amphineura,  being  dis- 
tinctly rei)resented  only  by  a  comparatively  snndl  pericar- 
dium surrounding  the  heart,  the  auricle  in  some  cases  not 
being  enclosed  by  it.  From  analogy  with  the  Ami)hineura, 
liowover,  the  rei)ioductive  organs  must  be  regarded  as  re])re- 
senting  a  j)ortion  of  the  enteroctul  whose  connection  with  the 
pericardium  has  been  completely  severed.  A  glandular  struc- 
ture, the  p(M-icardial  gland,  is  in  some  (lasteropods  developed 
by  the  folding  of  the  pericardial  walls,  and  has  aj)i)arently 
an  excrett)ry  function  acting  as  an  accessory  neplnidium  ;  it 
is  not,  however,  as  highly  developed  as  in  some  of  the  other 
Molluscan  groups. 

The  circulatory  organ  ])ossesses  in  some  forms  the  charac- 
teristic Molluscan  structure,  ctmsisting  of  un  uni)aired  ven- 
tricle lying  in  the  pericardium  and  receiving  the  blood  from 
two  lab^ral  wing-like  auricles.  In  nniuy  cases,  however,  as  al- 
r»>ady  pointed  out,  the  asymmetry  produced  by  the  develop- 
ment of  the  visceral  hump  iiih>cts  the  heart,  resulting  in  tht^ 
sui)pression  of  one  of  the  auricles,  that  of  the  left  lor  right) 
siile  (Fig.  i;)3).  In  such  cases  the  j)ersisting  auricle  nav 
secondarily  assume  a  terminal  position  with  regard  to  the 
ventricle,  and  the  latter,  instead  of  being  continued  into  an  ar- 
tery at  either  extremity,  gives  oil' a  single  artery  at  the  end  op- 
])osite  to  that  at  which  the  blood  enters  from  the  auricle,  this 
artery  dividing  into  two  nniin  trunks  which  distribute  the 
bh)od  to  the  various  regions  of  the  body.  Those  arteries  nun- 
be  coutiuued  as  distinct  tubes  with  definite  walls  for  some 


TYPE  MOLLUSC  A. 


299 


nportaiit 
oiuotioii, 
seis,  jiiul 
[  vertical 
il  liiinip 
I  wall  its 
jrizuiital 
;)  retract 
)iueiit  is 
onus  in 
,ckiii<jf  it. 
reduced 
eiiig  dis- 
pericar- 
ises  not 
liineura, 
LH  re])re- 
witli  the 
ar  struc- 
)vel()j)ed 
{lareutly 
Hum  ;  it 
he  otlier 

s  cliarac- 
•ed  ven- 
i()d  from 
3r,  as  al- 
levelop- 
j;  iu  the 
)r  ri^dit) 
clt  nay 
I  to  tlm 
to  an  ai- 
aendop- 
icl(>,  tliis 
)ute  the 
riea  nuiy 
or  some 


distance  from  the  heart,  but  sooner  or  later  the  blood  passes 
into  the  system  of  lacunar  spaces  constituting'  the  schijjoccel, 
whence  it  is  again  returned  to  the  auricle  through  a  series  of 
veins.  The  i)osition  of  the  single  auricle  with  reference  to  the 
hod.y  axis  differs  in  different  orders  of  Gasteropods,  in  accord- 


Fio.  183.-STHTICTDUK  OF  Si/cott/pi>.9  ra„nlk„lni,is.    The  miintlc  Is  divided  in 
tlie  iniddltj  liuc  aud  uuiicd  aside,  exposing  liu;  nuuitleciivitv. 


an  =  anus. 

cl  =  ctenidium. 
d(/  —  digestive  gland. 

t  =  intestine. 

n  =  nepiiiidiiini. 
no  =  nepliridial  opening. 

0  =  eye. 
op  =  opereiilinn. 


OK  -  osplinidinMi. 

p  =  pericardial  cavity. 
)>e  =  perus. 
pr  =  proboseLs. 
««■  =  siplio. 

/  -  lenlacle. 
te  =  testis. 

V  =  ventricle. 


I'd  =  vas  deferens. 
Tlie  arrows  show  tlic  op.inings  of  ncpIiiidiiini  to  llie  nianlle-olmmher  and  lo 

the  periciirdiuni. 

ance  with  the  varying  jjosition  of  the  branchia.  In  those 
t'Tnjs  in  which  the  l)ninchia  lies  in  front  of  the  liwirt  the 
fiiiricle  lies  at  the  anterior  end  of  tlie  ventricle,  while  when 
till!  branchia  is  posteriorly  situated  the  auricle  lies  behind 
t\iv  veutricle. 

rii.^  mouth   lies  in  all  Gasteropods   at   the  anterior  ex- 


tremity  of  the  body,  towards  tl 


le  ventral  surface  of  the  head 


300 


IN VEIi TEBRA  TE  MOIiPIIOLO G  T. 


I   1-^ 


and  opens  into  a  mouth-cavity  frequently  provided  with  two 
or  more  chitiuous  teeth.  The  pharynx  usually  receives  the 
ducts  of  a  pair  of  salivary  glands,  contains  a  well-developed 
radular  organ  in  practically  all  cases,  and  communicates 
posteriorly  with  a  tubular  (esophagus.  In  many  cases  the 
anterior  portion  of  the  digestive  tract  is  capable  of  being 
protruded  as  a  proboscis  (Fig.  lo3,  pr),  which  lies  when  re- 
tracted within  a  proboscis-sheath,  formed  by  a  circular  infold- 
ing of  the  body-wall  around  the  mouth.  The  intestine  (t)  is 
usually  more  or  less  coiled,  extending  into  the  visceral  hump, 
and  presents  a  stomach-like  enlargement  Avhich  receives 
the  ducts  of  the  digestive  gland  {dg),  a  structure  usually  well 
developed  and  forming  the  greater  portion  of  the  visceral 
hump.  The  intestine  terminates  in  a  straight  i)ortion,  the 
rectum  (r),  which  passes  forward  to  the  anus  {an),  Avhich,  as 
has  already  been  indicated,  lies  in  the  mantle-cavity,  slightly 
to  the  right,  but  occasionally'  to  the  left,  of  the  middle 
line,  its  position  depending  upon  the  amount  of  rotation 
which  the  mantle-cavity  and  the  associated  organs  have 
undergone.  It  should  bo  mentioned  that  in  one  suborder  of 
Gasteropods  the  pericardium  and  ventricle  have  wrapjjod 
themselves  around  the  rectum  in  Buch  a  way  that  the  diges- 
tive tube  seems  to  have  pejietrated  the  ventricle,  a  features 
which  will  later  be  seen  to  be  characteristic  of  one  of  the 
other  groups  of  Mollusca. 

The  nervous  system  has  the  arrangement  which  has  been 
di  scriluid  as  characteristic  of  tlie  Mollusca  (Fig.  124),  the 
peculiar  feature  being  the  crossing  of  the  p hi uro- parietal  con- 
nectives which  is  found  in  many  forms.  Numerous  modifica- 
tions of  the  typical  condition  are  to  be  found,  consisting 
])rincipally  in  (1)  th(^  concentration  of  the  ganglia,  more 
especially  the  cerebral,  pleural,  and  ])edal,  or  the  ])edal, 
phniral,  parietal,  and  visceral  (Fig.  139),  to  form  a  singli' 
mass;  (2)  in  the  su])])res8ion  in  Home  cases  of  one  of  the 
parietal  ganglia ;  and  (3)  in  the  occurrence  of  several  visceral 
ganglia.  In  accordance  with  the  flat  elongated  form  of  the 
foot  in  many  species,  the  nerve-cords  jiassing  backward  from 
the  pedal  ganglia  may  be  of  considerable  size,  and  further- 
more   nniy    be    connoctod    by    regularly-arranged    transverse 


TYPE  MOLLUSCA. 


301 


commissures,  recalling  the  condition  seen  in  the  Chitons,  as 
well  as  the  ladder-like  arrangement  of  the  ventral  nerve-cords 
of  the  Annelida,  though  there  cannot  in  the  Gasteropods  be 
any  question  of  metamerism  in  this  connection. 

Special  sense-organs  are  very  generally  well  developed  in 
the  Gasteropods,  The  tentacles  so  usually  found  upon  the 
head  have  probably  a  tactile  function  as  well  as  the  tentacular 
or  winglike  processes  sometimes  found  in  connection  with 
the  anterior  extremity  of  the  foot,  and  the  epipodial  ten- 
tacles Avhich  occur  in  some  forms  {llaliotis).  On  the  ventral 
side  of  the  bases  of  the  epipodial  tentacles  of  some  forms 
s})ocial  sensory  thickenings  have  been  found  which  havt^ 
suggested  a  compariscm  with  the  sense-organs  of  the  lateral 
line  of  the  Annelida,  a  comparison  which,  however,  at  present 
seems  rather  strained  ;  it  seems  probable,  notwithstanding 
their  innervation  from  the  pedal  ganglia,  that  these  sensory 
})atches  are  to  be  placed  in  the  same  category  as  the  osphra- 
dia  and  the  sensory  ridges  of  the  mantle-cavity  of  the  Chi- 
tons. Tlie  osphradia  (Fig.  188,  os)  in  all  Gasteropods  which 
are  provided  with  branchiie  are  associated  with  these  "igans' 
and  even  where  one  or  both  -mi^J^ 
branchiio  have  been  suppressed 
the  osphradia  may  still  persist. 
Eyes  (Fig.  134)  are  very  generally 
j)resent  in  the  Gasteropods,  being 
situated  at  the  base  of  tlie  ten- 
tacles, or  at  tlieir  summit  in  some 
forms.  Tiiey  present  a  veiy  uni- 
form structure  throughout  the 
group  and  arise  as  a  depression 
of  tin;  integument,  the  lips  of 
the  cavity  fusing  and  giving  rise 
to  a  glol)uhir  sac  lying  beneath 
th(i  ejiidermis,  which  I'emains  thin  and  transparcmt,  forming  an 
outer  i-ornea  U'<>\  I'he  cells  of  the  outer  wall  of  tlie  sa<r 
likewis(^  renniin  clear,  forming  the  inner  cornea,  while  over 
tli(>  lemaindtu"  of  the  wall  of  the  sac  they  are  sensor)  in 
function,  ]>igniented  cells   being  scattertMl   anh.ng   them,  tl 


Fid,  184.  — KvK  <»K  lliiliotiH  u\iU'r 
Pattkn). 

CO  —  coiiita. 
I  —  lens. 
rt  —  reliiia. 


iO 


two  together  forming  the  retiini  (>W).     The  nerve-fibres  pass- 


i  m 


302 


INVERTEBRATE  MORPHOLOGY. 


iug  to  the  eye  from  the  cerebral  ganglia  pass  through  an  optic 
ganglion  lying  beneath  the  optic  sac  and  are  distributed  to 
the  sensory  cells,  and  the  centre  of  the  sac  is  filled  up  by  a 
cuticular  mass  which  serves  as  a  refractive  lens  (/).  In  some 
forms  {Patella,  etc.)  the  development  of  the  eye  ceases  while 
it  is  still  in  the  cup  form,  there  being  then  no  formation  of 
corneal  layers  and  no  central  lens,  though  the  retina  is  usu- 
ally covered  by  a  thin  cuticular  layer.  In  some  species  of  a 
peculiar  genus  of  the  air-breathing  Gasteropods,  Onchidium, 
eyes  are  developed  upon  the  dorsal  surface  of  the  body,  the 
shell  being  lacking  and  the  visceral  hump  undeveloped.  In 
structure  these  eyes  differ  very  materially  from  those  usually 
occurring  in  the  Gasteropoda  and  will  be  described  later 
<p.  HI8). 

Otocysts  are  usually  imbedded  in  the  tissues  of  the  foot 
close  to  the  pedal  ganglia,  tl'ough  in  all  cases  they  receive 
their  innervation  from  the  cerebral  ganglia ;  they  have  the 
usual  sac-like  form  and  are  lined  with  sensory  hair-bearing 
cells  and  contain  otoliths. 

The  uephridia  of  the  Gasteropods  are  in  nearly  all  cases 
modified  from  the  original  typical  condition  in  accordance 
with  the  asymmetry  of  the  body  (Fig.  133,  re).  In  only  a  few 
forjns,  so  far  as  known  {FissureUa,  Patella),  are  two  functional 
nephridia,  opening  on  the  one  hand  into  the  pericardial 
cavity  and  on  the  other  to  the  exterior  through  the  mantle- 
cavity,  perfectly  developed.  In  other  forms,  such  as  Mali- 
Otis,  Turbo,  etc.,  both  iiephridia  are  present  and  are  struct- 
urally perfect,  though  the  left*  on*!  has  lost  its  secretory 
function,  but  in  the  majority  of  cases  the  left  (or,  in  forms 
Avith  a  left-handed  coiling  of  the  visceral  hump,  the  right) 
nephridium  is  conijiletely  aborted. 

The  Gasteropod;:  are  in  some  cases  bisexual,  in  others 
hermaphrodite.  The  reproductive  sac  (Fig.  133,  t)  is  quite 
unconnected  with  tlie  pericardial  enteroccel  and  is  an  un- 
paired structure  lying  in  the  visceral  Iniiiip.  The  ova  and 
si)ermat()Zoa  in  most  cases  reach  the  exterior  by  a  special 


*  The  terms  left  and  rislit  refer  ti>  tin-  position  of  tiio  iifi.liridiii  n^i  iliey  ate 
supposed  to  litive  becu  niniuged  in  llic  primillvo  aymmelricul  Oiistciopod. 


TYPE  MOLLUSC  A. 


303 


duct  {vd),  having  apparently  no  relation  to  the  nephridia  and 
opening  into  the  mantle-cavity  to  the  right  side  of  the  anus. 
In  the  more  primitive  Gasteropods,  however,  such  as  Haliofis, 
Fissurella,  and  Patella,  the  nephridia,  as  in  the  8olenogastres,' 
serve  as  reproductive  ducts ;  and  it  has  been  suggested  that 
the  special  reproductive  duct  of  the  remaining  Gasteropods 
may  represent  the  left  nephridium,  which  is  usually  described 
as  having  disappeared.  The  reproductive  duct,  especially  in 
hermaphrodite  forms,  has  developed  in  connection  with  it 
accessory  glandular  structures  a;i  well  ^^s  external  copulatory 
organs,  the  whole  reproductive  system  becoming  highly  com- 
plicated. An  account  of  the  more  important  arrangements 
will  be  more  satisfactorily  given  in  connection  with  the 
various  orders. 

1.  Order  Prosobranchia. 
The  Prosobranchia  are,  with  very  few  exceptions,  marine 
Gasteropods,  provided  with  well-developed  shells,  which  are 
usually  spirally  coiled,   the  height  of 
the  spiral  varying,  however,  in  different 
forms.     In  some,  such  as  Patella  and 
Fvisun'lla,    the     shell    has    a    simple 
conical   form,  without   any  indication 
of  a  spiral ;  and  since  these  forms  in 
many  respects  show  primitive   charac- 
ters, it  might  be   supposed  that  this 
type  of  shell  was  also  primitive.    These 
very  forms,  however,    show   also   that 

asymmetryof  parts,  which  is  character. F.a.l35.-SHKu-s OF  Pmoso- 
istic   for   the   Gasterojjods,  and  which     "hancii      (Jastkuoi-odh. 

accompanies  the  rotation  of  the  mantle-     ^'     Acimm    ti'studlnnliH 

ciivity,  and  furtluM-moro,  in    Fi.s.surella     "*"**''  ""'''"*=    Z^- '/"''""^ 

11         J  f    .•       ..,.        .  'lifter  Lkunimi;  C.  Ttirvltt'lln. 

Ht   least,    a    distinct   indicaticn    of    a     (after  leun.h) 

si)iral  coiling,  is  present  in  the  shells  of 

young  animals.     It  seems  more  prol)able,  accordingly,  that 

these  conical  shells  are  to  be  regarded  as  secondary  niodid. 

cations  of  an  originally  s])irally-coiled  shell. 

The  mantle-cavity  is  situated  in  front  of  the  well-devel- 
oped visceral  hump,  and  is  usually  somewhat  cajjacious,  com. 


r« 


304 


IN VERTEBitA TE  MORPHOL 00  T. 


nuinicating  with  tlie  exterior  freelj-.  lu  some  forms  the 
mantle  is  slit  from  itb  margin  upwards  and  backwards,  a 
corresponding  slit  occurring  in  the  shell  {Ithiarginula) .  In 
HaUotis  and  Pleurotomaria  the  alit  in  the  sliell  becomes 
closed  at  regular  intervals,  producing  a  row  of  round  perfora- 
tions, beneath  which  lies  the  niantle-slit,  and  through  which 
water  finds  a  read}-  exit  from  the  mantle-cavity,  and,  in  Fis- 
surelhi,  in  which  at  an  early  stage  the  margin  of  the  shell 
possesses  a  slit,  by  the  subsequent  growth  and  obliteration  of 
the  spiral  coiling  the  slit  becomes  converted  into  an  ai)erture 
which  lies  almost  at  the  apex  of  the  conical  shell  and  leads 
into  the  mantle-cavity,  functioning  as  a  means  of  exit  of  the 
water  and  excrementa  from  that  cavity.  In  the  greater  num- 
ber of  forms,  however,  such  slits  or  apertures  do  not  exist ; 
but  one  finds  frequently  the  margin  of  the  mantle  produced 
at  one  point  on  the  left  side  into  a  projecting  narrow  lobe 
whose  edges  may  be  brought  into  opposition,  thus  producing 
a  tube  or  siphon  through  which  water  may  pass  into  the 
mantle-cavity.  Where  this  siphon  is  Avell  developed  a  dis- 
tinct notch  is  found  in  the  margin  of  the  shell,  through  which 
it  may  be  protruded,  or  else  the  lips  of  the  notch  are  pro- 
longed so  as  to  form  a  grooved  process,  the  siphonal  canal,  in 
which  the  siphon  lies,  being  by  these  arrangements  able  to 
function  even  Avhen  the  moutli  of  the  shell  is  closed  by  the 
operculum.  In  many  forms  the  mantle-folds  are  sufficiently 
large  to  allow  of  their  being  reflected  over  the  outer  surface 
of  the  shell  when  tlie  body  is  fully  protruded. 

The  foot  is  as  a  rule  adapted  for  creejjing,  but  in  many 
cases  is  differentiated  into  pro-,  meso-  and  metaj)odium,  tlui 
last  usually  bearing  a  chitiuous  or  more  or  less  calcified 
operculum.  In  certain  forms  belonging  to  a  group  of  pelagic 
forms,  however,  which  Avere  formerly  associated  together  as  a 
distinct  order,  the  IMeropoda  (Fig.  138),  the  pro-  and  meso- 
podium  are  modified  into  a  keol-like  structure  and  bear  a 
peculiar  sucker.  The  ei)ip()dium  is  frequently  developed  in 
the  Prosobranchia,  especially  in  the  more  primitive  sjjccies  - 
most  frequently,  however,  being  reduced  to  tentacle-  or  lolu!- 
3esses  arising  from  the  sides  of  the  foot. 


lik< 


proc< 


In  the  majority  (Fig.  133)  of  forms  there  is  but  a  singl< 


TYPE  MOLLUSC  A. 


305 


irms  the 
wards,  a 
ula).  In 
becomes 
.  perfora- 
;li  which 
I,  in  Fis- 
bhe  shell 
iratiou  of 
a})erture 
iiid  leads 
xit  of  the 
iter  nura- 
ot  exist ; 
produced 
•row  lobe 
»rodueii)g 

into  the 
ed  a  dis- 
gh  which 

are  pro- 
.  canal,  in 
s  able  to 
id  hy  the 
itliciently 
r  surface 

in  many 
diuui,  the 

calcified 
i)f  pelaj^ic 
ather  as  a 
lud  meso- 
id  bear  a 
eloped  iu 
sjjecies-  - 
B-  or  Idbe- 

t  a  singltf 


branchia  Avhich  lies  iu  front  of  the  heart,  whence  the  name  of 
the  order,  but  iu  a  few  genera  the  original  left  gill  also  per- 
sists. In  many  forms  a  gland  is  developed  in  the  floor  of  the 
mantle-cavity  close  to  the  rectum— hence  called  the  adrectal 
gland — which  in  some  forms,  e.g.  Murex  secretes  a  purple 
pigment.  The  rotation  of  the  mantle-cavity  and  the  associated 
organs  has  called  forth  a  crossiug  of  the  pleuro-parietal  nerve- 
cords,  a  feature  which  is  lacking  in  the  other  orders  and 
therefore  forms  a  characteristic  of  the  Prosobranchs. 

In  all  but  a  few  cases  the  members  of  the  order  are  bisex- 
ual, the  unpaired  reproductive  gland  lying  in  the  visceral 
hump.  The  oviduct  hii^s  iu  connection  with  it  one  or  more 
receptacula  semiuis  and  dilates  into  a  glandular  uterus  in 
whicli  the  eggs  are  su])p]ied  with  the  albumen  in  which  they 
are  usually  imbedded  and  also  surrounded  by  a  shell.  In 
the  males,  except  in  the  more  primitive  forms,  there  is  present 
a  well-developed  intromittent  organ  or  penis  (Fig.  133,  jot^), 
situated  upon  the  right  side  of  the  head  or  neck  and  there- 
fore removed  at  some  distance  from  the  opening  of  the  vas 
deferens  into  the  mantle  cavity.  A  groove  or  tube  extends, 
however,  from  the  reproductive  orifice  to  the  grooved  or  tubu- 
lar penis,  and  along  this  groove  or  tube,  by  the  ciliary  action 
of  the  cells  liuing  it,  the  seminal  fluid  is  carried. 

1.  Suborder  Diotocardia. 

This  suborder  includes  the  more  primitive  Prosobranchs, 
iu  which,  although  a  considerable  rotation  has  occurred,  yet 
nevertheless  the  abortion  of  the  organs  of  the  original  left 
side  of  the  body  has  not  been  carried  very  far.  Thus,  except 
in  Patella  and  some  allied  forms,  there  are  two  auricles  to  the 
heart,  although  iu  Turho,  7'r<ichm,  Neritina,  and  allied  genera 
that  of  the  right  side  (i.e.,  the  original  left  one)  does  not  coni- 
numicate  with  the  ventricle.  Attention  may  again  be  called 
to  the  fact  that  in  those  forms  which  possess  two  functional 
auricles  the  ventricle  and  pericardium  have  wrai)i)ed  them- 
selves  round  the  rectum  which  seems  to  ))erf(n'ato  the  ventri- 
cle. Such  ffivnig  as  Haliod^,  FiHsnrella,  .and  PlcnrohniK^ria  pos- 
sess two  branchitr,  but  in  the  majority  of  the  members  of  the 


<=5: 


'S 


if  ,*- 


(^ 


soe 


INVEliTEDRATE  MORPHOLOGY. 


|fioup  only  one  is  present,  while  iu  Patella  both  have  disap- 
jjeared,  their  phiee  haviuj;  been  taken  by  respiratory  folds 
of  the  mantle.     Both  kidneys  are  invariably  present. 

The  primitive  character  of  the  suborder  is  further  shown 
in  the  absence  of  certain  structures  found  in  more  specialized 
forms.  Thus  the  foot  is  flat  and  undifferentiated  into  pro-, 
meso-,  and  nietapodiura  ;  the  anterior  part  of  tlio  digestive  tract 
is  not  evertible  as  a  proboscis ;  there  is  no  siphonal  prolonga- 
tion of  the  mantle,  and  no  notch  or  siphonal  groove  on  the 
margin  of  the  shell ;  and  there  is  no  penis.  On  the  other  hand 
the  epipodium  is  usually  well  developed,  as  are  also  the  pedal 
nerve-cortls,  Avhicli  are  connected  by  numerous  cross-commis- 
sures. 

A  further  distinguishing  feature  of  the  suborder  is  the 
arrangement  of  the  teeth  of  the  radula.  Each  transverse  row 
of  teeth  presents  an  indefinite  number  of  marginal  teeth,  usu- 
ally a  single  lateral,  a  single  median,  and  a  varying  number 
of  admedian  teeth,  an  arrangement  known  as  rhipidoglossate. 
Thus  in  Haliotis  the  arrangement  is  indicated  by  the  formula 


Fig.  136.— DiiNTiTioN  of  ^jw/zms  (after  Lanrestkr). 

X,  1,  5, 1,  5,  1,  X  ;  in  FissnreHa  by  ,r,  1,  4, 1,  4, 1,  x  ;  and  in  ^ 
chus  (Fig.  136)  and  T%irho  by  x,  0,  5,  1,  5,  0.  x,  the  single  lateral 
tooth  being  absent  in  these  forms.  In  Patella,  however,  an- 
other arrangement  is  found  characterized  by  the  occurrence 
of  oidy  a  small  number  of  marginal  teeth  and  by  the  absence 
of  the  median,  the  formula  being  3,  1,  2,  0,  2,  1,  3 ;  this  ar- 
rangement is  termed  docoglossate. 


2.   Suborder  Monotocardia. 

In  this  suborder  the  effect  of  the  pressure  of  the  visceral 
hump  on  tl!e(H-g:vi!H  of  tlif^  loft  ,sido  of  tlie  nmntlo-cavity  is  more 
pronounced  than  in  the  Diotocardia.      The  heart  possesses  a 


^e  disap- 
)ry  folds 

31"  shown 
ecialized 
iito  pi'(i-, 
tive  tract 
H'olouga- 
3  on  the 
;ier  hand 
lie  pedal 
•commis- 

31'  is  the 
erse  row 
eth,  usu- 

number 
glossate. 

formula 


TYPE  MOLLUSC  A. 


307 


.  m  J 
le  lateral 
ever,  an- 
eurrence 
absence 
this  ar- 


visceral 

i'  is  nion? 
^sesses  a 


single  auricle  only,  except  in  Cyprcea,  where  the  rudiment  of  a 
second  occurs,  and  throughout  the  group  but  a  single  nephrid- 
ium  is  present.  There  is  never  more  than  a  single  gill,  which 
is  usually  more  or  less  united  to  the  mantle-wall  and  bears, 
lateral  branches  only  ujion  one  side. 

The  foot  is  in  some  cases  Hat  and  broad,  as  in  the  Dioto- 
cardia,  and  in  such  cases  may  possess  the  parallel  pedal  nerve- 
cords  with  transverse  commissures  as  in  Cyprmi  and  J\dudina, 
but  usually  it  becomes  more  or  less  differentiated,  a  propodi- 
um  being  in  many  cases  well  defined  {Stromhus,  Nutica),  while 
a  chitinous  or  calcareous  operculum  is  usually  carried  by  the 
luetapodium,  and  the  pedal  nerve-cords  are  very  much  re- 
duced or  wanting,  the  pedal  ganglia  being  on  the  other  hand 
more  highly  developed  than  in  the  Diotocardia.  The  epipo- 
dium  is  usually  entirely  wanting,  and  when  present  is  but 
slightly  developed,  reaching  its  fullest  development  as  a  con- 
tinuous fold  upon  the  sides  of  the  foot  only  in  lanthina.  In 
Palmiina  it  is  represented  by  two  anteriorly-situated  tentacle- 
like lobes,  and  in  CuJyptrma  by  a  semicircular  fold  on  each 
side  of  the  neck  region. 

The  Monotocardia  are  further  distinguished  by  the  fre- 
cpient  occurrence  of  a  well-developed  siphon  and  a  more  or 
less  devehjped  siphon  groove  at  the  margin  of  the  shell,  and 
furthermore  a  well-developed  penis  is  usually  present. 

The  anterior  portion  of  the  digestive  tract  is  in  many  forms 
capable  of  being  protruded  as  a  proboscis.  The  arrangement 
of  the  teeth  of  the  radula  varies  considerably  in  different 
forms,  but  the  rhipidoglossate  arrangement  is  not  represented. 
In  one  group,  including  the  genera  Cypnea,  Nat'ica  (Fig.  137, 
A),  Littorina  (the  periwinkles),  Calyptrcpa,  :^lromhu.s,  etc.,  the 
tionioglossate  arrangement  is  found,  represented  by  the  for- 
mula 2  or  3,  1, 1, 1,  2  or  3,  the  admedian  teeth,  however,  being 
very  similar  to  the  lateral.  In  other  cases  but  a  single  median 
tooth  or  the  median  with  a  single  admedian  on  each  side  is 
found,  as  in  Fmus,  Baccinum  (the  whelks),  Nmsn  (Fig.  137,  B), 
Jlurex,  Purpura,  OJiva,  Marginella,  etc.,  forming  the  rachi- 
glossate  arrangement  represented  by  the  formulas  — ,  1,  — ,  or 
1, 1, 1.  In  Terehra,  Conus,  PJeurotoma  (Fig.  137,  C\  and  allied 
genera  the  median  tooth  is  absent,  and  the  single  admedian 


■ii 


•^ 


i 


808 


INVERTEBRATE  MORPHOLOGY. 


tooth  on  either  side  peculiarly  long,  forming  the  toxiglossate 
arrangement  with  a  formula  1,  0,  1 ;  and  finally  certain  forms, 
such  as  lanthina,  Scalaria  (Fig.  137,  J)),  Solarium,  etc.,  have  a 
ptenoglossate  arrangement  in  which  the  median  is  wanting 
but  in  which  there  are  a  large  number  of  admedians,  x,  0,  x. 

The  suborder  is  relatively  very  rich  in  species,  and  conse- 
quently considerable  variety  of  form  is  found.  The  majority 
are  marine,  but  a  few  are  fresh-water  or  even  terrestrial  in 
habitat.  In  these  latter  adaptations  to  their  mode  of  life  are 
found  in  modifications  of  the  respiratory  jjrocesses.     In  Am- 


FiG.  137.— J.,  Dentition  o¥  Natica  ;  B.  of  Nassa;  C,  of  Pleurotoma ;  D, 

OF  Scalaria  (from  Bronn). 

pullaria  the  single  branchia  persists,  but  in  addition  a  com- 
paratively capacious  "  lung  cavity  "  is  formed  by  a  fold  of  the 
mantle,  its  walls  being  richly  supplied  with  blood-vessels  and 
its  cavity  being  in  communication  with  the  exterior,  so  that 
air  can  be  taken  into  and  expelled  from  it.  The  species  of 
this  genus  live  partly  in  fresh  water  and  partly  are  terrestrial, 
but  in  other  forms,  such  as  Cyclostoma,  which  are  purely  ter- 
restrial, the  branchia  has  entirely  aborted,  respiration  being 
aerial  and  performed  by  the  highly  vascular  wall  of  the 
mantle-cavity. 

The  majority  of  the  marine  Monotocardia  have  a  creep- 
ing habit,  but  a  number  are  pelagic  and  form  a  group  pre- 
senting many  adaptive  peculiarities  which  obtained  for  it  the 
dignity  of  an  order  in  older  classifications.  The  members  of 
this  group,  Heteropoda,  are  more  or  less  transparent  aninials, 

L-esent  few  di 


some 


except 


pr< 


fences 


glossate 
u  forms, 
,  have  a 
wautiug 

tX/J      \jy      VU* 

l1  couse- 
najority 
itrial  iu 
'  life  are 
Iu  Am- 


}io7na  ;  D, 


11  a  com- 
Id  of  the 
sels  and 
so  that 
»ecies  of 
I'restrial, 
rely  ter- 
:)M  beiiij4 
I   of  the 

a  creeji- 
5up  pre- 
or  it  the 
nbers  of 
aninials, 
Sereuces 


TYPE  MOLLUSCA. 


309 


from  the  other  Mouotocardia,  while  others  are  extensively 
modified.  The  gemis  Atalanta  possessc  a  large  transparent 
shell  within  which  the  animal  can  be  completely  retracted. 
The  foot  is  no  longer  adapted  for  creeping,  but  is  differenti- 
ated into  a  laterally  flattened  keel-like  pro-  and  mesopodium 
which  bears  a  sucker  on  its  posterior  surface,  and  a  metapo- 
dium  provided  with  an  operculum.     Iu  Carinaria  (Fig.  138) 


Fig.  138. — Stuuctuke  of  Carinaria  mediteiranea  (after  Owen). 
ao  =  aoitii. 
b  =  buccal  mass. 
eg  =  cerebral  gangliou. 
ct  =  ctenidium. 


h  =  liL'ait,. 
i=  intestine. 
I  =  liver. 
mp  =  iiusopodiuni. 


0  =  eye. 

p  =  penis. 
peg  =  pedal  ganglion. 
s  =  salivary  gland. 
su  =  sucker. 
te  =  t  estis. 
I'd  =  vas  deferens. 
vg  =  visceral  ganglion. 


m  =  seminal  vesicle. 

the  visceral  hump  is  reduced  to  a  comparatively  small  mass 
upon  the  dorsal  surface  of  the  elongated  body  and  is  enclosed 
iu  a  transparent  shell  shaped  like  a  liberty-cap.  The  pro-  and 
mesopodium  have  the  form  of  a  plate  hanging  down  from 
about  the  middle  of  the  under-surface  of  the  body,  and  the 
metapodium  is  directed  backwards,  forming  in  reality  the 
posterior  portion  of  the  body.  The  same  relationships  of  the 
foot  are  found  in  Pterotrachen,  which  presents  the  extreme  of 
modification  found  iu  this  grou])  ;  in  this  form  the  visceral 
liump  is  still  more  reduced  than  in  (hrimma,  forming  only  a 
small  oval  mass  imbedded  in  tlie  dorsal  surface  of  the  body 
and  being  destitute  of  any  shell.    Considering  these  two  forms. 


rrl 


?»' 


,1- 

u 


310 


IN  VERTEBltA  TE  MORPIIOLOO  Y. 


J'terotrachm  siud  Cannaria,  by  themselveH,  the  formatiou  of 
a  senanite  order  for  their  reception  woukl  perhaps  be  justi- 
UtilAe,  hni  Ataltmta  shows  their  close  rehitioiiships  with  the 
Prosobrauchia  aucl  indicates  their  true  position  as  Monoto- 
cardia. 


f : 


2.  Order  Opisthobranchia. 

The  Oi)isthobranchs  are  exclusively  marine  forms,  present- 
ing numerous  modifications  of  shape  and  structure,  but  all 
agreeing  in  certain  importaut  particulars.  The  rotation  of 
the  mantle-cavity  has  uot  proceeded  quite  so  far  as  in  the 
Prosobranchs,  the  cavity  and  its  organs  lyiug  upon  the  right 
side  of  the  body,  but  at  the  same  time  the  abortion  of  the 
organs  of  the  primitively  left  side  of  the  body  has  occurred. 
Thus  in  those  forms  which  possess  respiratory  oi-gans  homol- 
ogous with  the  branchiie  of  the  Pros(jbrauchs,  but  one  (that 
of  the  right  side)  is  present,  and  with  this  character  is  associ- 
ated the  occurrence  in  the  heart  of  but  a  single  auricle, 
which  lies  behind  the  ventricle.  Oidy  one  nephridium  occurs, 
and  a  distinction  from  the  Monotocardiate  Prosobranchs  is 
found  in  the  fact  that  the  branchia  when  present  lies  as  in- 
dicated by  the  position  of  the  auricle,  behind  the  heart — the 
name  bestowed  upon  the  order  being  suggested  by  this  pecul- 
iarity. 

A  more  important  distinguishing  character  perhaps  is,, 
however,  to  be  found  in  the  arrangement  of  the  nerve-cords. 
A  well-marked  tendency  towards  an  aggregation  of  the  vari- 
ous ganglia  to  a  complex  mass  lying  behind  the  pharynx  may 
be  considered  a  characteristic  of  the  Opisthobranchs.  One 
or  both  parietal  ganglia  may  disappear,  and  in  some  cases 
where  there  is  a  marked  concentration  of  the  ganglia  the 
visceral  ganglion  may  also  be  Unrepresented,  though  usually 
from  one  to  three  such  ganglia  may  be  distinguished.  In  the 
figure  of  the  nervous  system  of  Fio7in  (Fig.  139)  the  conceutni- 
tion  of  the  ganglia  is  well  marked,  but  a  deciiled  asymmetry 
is  made  evident  in  some  forms  by  the  existence  of  a  single 
parietal  ganglion  and  of  three  visceral  ganglia.  In  Fiona, 
however,  the  ganglionic  concentration  has  been  carried  still 


TYPE  MOLLUSC  A. 


311 


utiou  of 
be  justi- 
witii  the 
Moiioto- 


preseut- 
but  nil 
itiou  of 
i  in  tbe 
lie  ri^ht 
1  of  tlie 
ecurred. 
I  liomol- 
ue  (that 
!  associ- 
auricle, 

I  occuirs, 
inchs  is 
s  as  in- 
art — tho 
is  pecul- 

laps  is,, 
'e-cords. 
he  vari- 
.'nx  may 
s.  One 
16  cases 
glia  tlio 
usually 
In  the 

II  centra- 
mine  try 
1  single 
I  Fiona, 
ied  still 


Fig.  139.— Nervous  System  of 
Fiona  atlantica  (after  Heroh  from 
Gkoenbaur). 

A  =  cerebio-pleurovisceral    gaii- 

[glioii. 
ion. 


farther,  and  at  the  same  time  by  the  suppression  of  the 
l)arietal  ganglion  as  a  distinct  mass  an  apparent  symmetry 
has  resulted.  Another  notable 
feature  is  the  usual  absence  of  any 
apparent  crossing  of  the  nerve- 
cords.  This  condition,  however,  is 
probably  due  to  the  concentration 
of  the  ganglia,  Avhereby  the  chias- 
toneurism  is  obscured,  one  of  the 
most  primitive  of  recent  Opistho- 
brauchs,  Acta'on,  presenting  well- 
marked  chiastoneurism,  associ- 
ated with  a  somewhat  discrete 
arrangement  of  the  ganglia. 

With   regard   to   many   other  ^  =  P«l"l  g'i"J?»i'>'' 

-      ,  i.     ii     •  .  C7  =  buccal  can <;]ioii. 

features  of  their  anatomy  con-  n  ^  .as.ro-a.so,,i,a.real  ganglion, 
siderable  variations  are  to  be  e  =  pedal  conmii.ssure. 
found.  Thus  in  some  forms  a  ^'  =  visceral  conunissme. 
well-developed  spirally-coiled  visceral  hump  is  developed, 
while  in  others  it  loses  its  spiral  arrangement,  and  in  others 
again  is  elongated  in  the  direction  of  the  foot  and  can  hardly 
be  said  to  exist,  S(j,  too,  with  the  occurrence  of  the  shell, 
mantle,  and  branchije ;  all  are  well  developed  in  some  forms, 
but  entirely  absent  in  others.  These  peculiarities  will  be  more 
conveniently  referred  to  in  connection  with  the  various  groups, 
and  it  is  only  necessary  here  to  refer  to  another  feature  in 
addition  to  those  already  given,  which  is  common  to  all  the 
members  of  the  order— i.e.,  the  hermaphroditic  character  of 
the  reproductive  gland. 

This  forms  part  of  the  vi^-eral  mass  and  is  usually  com- 
posed of  numerous  lobes,  these  again  being  divided  into 
secondary  lobes  or  acini,  the  lining  epithelium  of  which 
give  rise  to  both  ova  and  spermatozoa.  In  some  forms, 
such  as  Bulla  and  Aplyda,  both  elements  are  formed  in  ail 
the  acini ;  but  in  others,  such  as  Doris,  Janus,  Pteropoda,  etc., 
the  epithelium  of  the  terminal  acini  gives  rise  to  ova  only  ;  the 
epithelium  of  the  lobes,  i.e.,  the  central  portions  of  the  gland, 
producing  spermatozoa.  Whether  or  not,  however,  there  be 
such  a  separation  of  the  epithelium  into   male  and  female 


a 


i 

mi 


ii4 


.8..: 
t 


312 


INYERTEBRA TE  MORPHOLOG  Y. 


areas,  the  reproductive  elemeuts  make  their  way  into  a  com- 
mon hermaphrodite  duct,  which  presents  variations  of  structure 
in  diti'erent  forms  and  receives  the  secretion  of  certain  acces- 
sory ghmds.  In  its  simplest  form,  as  seen  for  instance  in 
Aplysia,  the  duct  runs  forward,  pursuing  a  somewhat  tortuous 
course  and  becomes  surrounded  by  an  (dbummiparom  ghaut, 
from  which  it  receives  a  viscid  secretion,  Avithin  which  the 
ova  become  imbedded  just  in  front  of  the  point  where  tlie 
ghmd  opens  into  the  duct.  The  Litter  lias  attached  to  it  a 
pouch-like  structure,  the  vesicida  seminalls,  and  is  continued 
on  as  a  somewhat  wider  tube  to  open  to  the  exterior  at  the 
genital  pore  situated  on  the  right  side  of  the  body,  shortly 
before  reaching  the  pore,  however,  receiving  a  duct  from  a 
globular  sac,  the  spermatheca.  From  the  anterior  edge  of  the 
pore  a  groove,  the  seminal  groove,  extends  along  the  right 
side  of  the  body  to  the  neck  region,  where  it  e?ids  in  a  mus- 
cular evertible  penis,  situated  near  the  anterior  right  tentacle. 
It  seems  probable  that  the  spermatozoa  mature  before  the 
ova,  and  passing  to  the  vesicula  are  stored  up  there.  During 
copul!.,tion  the  seminal  fluid  is  transferred  through  the  penis 
to  the  sjiermatheca  of  another  individual  (])erliaps  the  trans- 
ference is  a  mutual  interchange),  and  when  later  the  ova  pass 
along  the  duct  they  are  im])regnated  by  the  spermatozoa 
so  stored  &yfSi,y,  a  cross-fertilization  being  thus  brought 
about. 

This  arrangement  of  the  reproductive  duct  is  found  in  tlie 
more  primitive  Opisthobranchs,  i.e.,  in  those  in  winch  the 
mantle-lobe  still  persists,  and  in  the  group  Pteropoda]  in 
the  more  highly-modified  forms,  such  us  Doris,  A'Jolis,  etc., 
and,  among  tlie  more  siinph^  forms,  in  PlenroJyninvhn'a  tlic 
heriiiaplirodite  duct  divides  into  an  oviduct  and  a  vas  deferens. 
'J'he  former  after  receiving  the  spermathecal  duct  o])ens  into 
n  genital  atrium,  with  which  communicate  also  the  albuniiiii|)ii- 
rous  gland  and  a  nidnmentoJ  <jlaud,  which  maiiufacitures  tho 
outer  shell-like  investment  of  the  ova.  The  vas  deferens,  after 
a  more  or  less  tortuous  course,  enters  the  muscular  sadikc 
penis-sheath  which  communicatt's  with  the  genital  atrium;  tlic 
enlarged  termination  of  the  vas,  the  ])enis,  being  thus  capahh' 
of  eversion  through  th«>  pore  by  which  the  atrium  communicates 


'  Si 


TYPE  MOLLUSC  A. 


313 


o  a  cora- 
structure 
liii  .acces- 
stance  in 
;  tortuous 
mfi  gland, 
liich  the 
here  the 

3ll  to    it  !l 

soutiuueil 
or  at  the 
y,  shortly 
it  from  a 
Ige  of  the 
the  right 
11  a  m US- 
tentacle, 
efore  the 
During 
the  penis 
the  trans- 
ova  pass 
rniatozoa 
brought 

nd  in  the 
hich  the 
>p()da ;  in 
hJis,  etc., 
u'luvn  the 
i  ile/eycvu. 
i)pnH  inti) 
>uniiiii|);i- 
tnrcH  the 
'ons,  after 
ir  Hadiki' 
riuni;  tin 
s  capalili 
inmicalcs 


™ilh  tl,e  exterior.  This  coudition  seems  to  be  a  seeoiidarv 
mochhca  .on  of  oue  in  which  the  oviduct  aud  JultZ 
opeu  nulepemlently  at  widely  .separated  ,,oint.s-a  couditZ 
which  ,8  represented  by  a  few  Opisthobrauchs. 

1.  Suborder   TecUiranclUa. 

The  Tectibraiichiates  are  those  Opisthobrauchs  which 
present  the  smal  *st  amount  of  modification  from  wha  1,  ' 
been  considered  the  typical  Gasteropod  structure.  A  n  e 
or  less  developed  mantle-fold  is  usually  present,  someti.ne! 
sufcciently  voluminous  to  cover  in  the  s  ngle  branchiTw  i  h 
pei..sts  (/«.).  but  frequently  represented  only'  a    li 

,        ,  ,nf\    ;  ™'"^'  «■"""■"">■  V^o^oat,  sometbnes  well  de- 
veloped (BMa),  but  in  other  cases  reduced   to  a  plate-1  ke 
structure  enclosed  within  the  mantle  which  has  been  reflected 
overit  and  the  lips  of  the  reflected  portion  meeting  .and?:    n1 
(.Vy.v«,,  /•fc«™/«.,„,c;,.,).     The  visceral  hump,  h.nvever  is  "^ 
a  n,  e    ow  and  elongate,!  in  the  direction  „f  the  loug  axis  o 
the  body  mstea,!  of  at  right  angles  to  it,  as  in  the  matritv  o 
IVosobranchs      In  many  n.en.bers  of  the  group  the  Wt  poB 
s  sses  a  broad  creepn.g  s„rfa..c  b„t  its  n.argins  are  prolonged 
mto  broad  thm  wmgs,  the  pern;,,*',,,  which  may  be  bent  m, 
wards,  as  „,  Aply,;,,,  ,„  ,,  „,„„,,»  j,,  „„^.|„^^  ^^^^  "P 

Ihe  lectibranchiates  are  divisible  into  two  groups  accor,! 
".«  to    he,r  habits,  in  accord.ance  with  which  tl.e  fo,      of7  J 
loot  an.l  especally  of  the  parapo.lia  is  n,o,Iitied.    Those  for    s 
w  noh  ,«,ssess  a  broa.l  flat  sole  to  the  foot  have  a  c^e!  i:; 
liabit,  but  there  are  n.any  hums  wliich  are  pelagic  in  Imbit 

U  .H  ,m,d„  of  l,le,  and  were  conse,p,ently  classified  a  one  tin.e 
as  a  d.stn.ct  or,ler,  the  P™,„n,„u,  an,l  conse.inentiv  cal  r 
^|ec,..d  menfon.     ()m,  of  the  n.ost  characteristic  features 

.    «n,up  ,s  the  foot,  which  is  limited  to  the  anterior  po rti,  „ 
"I   the  body  and  insists  of  a  small   .n-.li,,,.   „„,,-o,    -,1, 
i.Ueral   wi Hl,„    ,: .■  .        7^ •   r"!t.oi.  .md  tw, 


ileral  wing-like   parapodia 


tiled 


■an   portU)u,   au<l    by  tho   rajiid    11 


arising   from    the   sides   of  tl 


appmg  of  which   tl 


ro 
le 
le 


314 


IN  VERTEBRA  TE  MORPIIO  LOOT. 


animals  are  propelled  through  the  water.  In  their  general 
form  much  diversity  is  observable.  In  accordance  with  their 
pelagic  habits  the  majority  are  more  or  less  transparent ;  and 
some,  the  Gy mnosomata,  e.g.  l*neumoderma,  Clione,  etc.,  are 
entirely  destitute  of  a  shell,  mantle,  and,  except  in  Pmumo- 
derma  and  its  allies,  of  a  branchia.  Others,  the  IViecosomata, 
possess  these  structures,  however — the  shell  in  Li7nacina  beiug 
spirally  coiled,  the  mantle-cavity  situated    in  front  of  the 


Fio.  iiO.—lIyalea  complnnata  (after  Gkcbnbaur,  from  Hertwig). 
rt  =  anus.  m  =  nmntle. 

br  =  bituicbisB.  oe  =  a'Hopljiigus. 

c  =  heart.  re  =  lu-phridiii. 

O  =  reproductive  orgaus.  v  =  stomiu'h. 

h  =  digestive  gland.  //  =  pedal  ganglion. 

visceral  hump  beiug  without  a  branchia ;  in  Sfyliohi  the  shell 
is  not  coiled,  but  is  cone-shaped  and  bilaterally  symmetrical, 
the  mantle-cavity  containing  a  gill  ;  while  in  ('!/iithuJiofhsi.s  the 
original  shell  is  replaced  by  a  cartilaginous  case  formed  by 
the  subepidermal  tissues  of  the  mantle,  and  the  voluminous 
mantle-cavity  contains  no  gill.  The  head  of  the  Gymnoso- 
muta  carries  a  non-retractile  jiroboscis,  at  the  extremity 
of  which  is  Hituated  the  nioutl!-,  and.  it  iiuiv  furthermore  bear 
in  addition  to  the  tentacles  usually  present  peculiar  tentacle- 
like  processes,  sometimes  provided  with  suckers  and  perhaps 


TYPE  MOLLUSC  A. 


315 


modifications  of  portions  of  the  foot,  being  innervated  from 
the  pedal  ganglia.  In  these  forms  also  fringed  or  simple  pro- 
cesses of  the  posterior  portion  of  the  body  occur  which  serve 
as  respiratory  organs,  though  they  are  not  homologous  with 
tJie  true  branchia  which  in  Pneumoderma  coexist  with  them. 

3.  Suborder  Nudihmnchia. 

In  the  Nudibranchs  the   visceral  hump   has  undergone 
elongation  parallel  with  the  long  axis  of  the  foot,  from  which  it 
is  not  distinctly  marked  off,  and  an  apparent  bilateral  sym- 
metry is  manifested  by  the  body.     This  condition,  however, 
is  evidently  entirely  secondary,  as  is  shown  by  the  structure 
of  the  heart  and  nephridium,  in  which  the  usual  asymmetry  is 
well  marked.    There  is  no  shell,  mantle,  or  ctenidia.    Adaptive 
branchiie  are,  however,  frequently  developed,  as  in  Pleurophyl- 
lidia,  where  they  form   a  series  of  folds 
which  lie  in  a  groove  at  the  side  of  the 
body  and  recall  somewhat  the  arrange- 
ment in  the  Chitonidie,  or  in  Doris,  where 
they   surround   the   anus,   which   has   a 
dorsal  position,  and  form  a  circle  of  pin- 
nate processes.     In  the  pelagic  PhyUirhoe 
and  in  the  creeping  Limaponfia,  however, 
there  is  no  trace  of  respiratory  organs. 
Many   forms   (Fig.   141),  such  as  Mali's, 
FacelUna,  and  their  allies,  bear  upon  the 
dorsal  surface  of  the   body  numbers  of 
fiuger-Iike  processes  usually  arranged  in 
bunches,  and  frequently  brightly  colored. 
These  cemfa  frequently  enclose  branches 
from  the  intestine  which  correspond  to 
the  digestive  gland  of  other  forms,  and  „      ,,,       ' 
bear  at  their  extremities  a  sac  in  which       "        '  ~  ^'^"'""^^• 
are  developed  uematocysts.    Tliese  organs 
are  usually  richly  provided  with  blood- 
vessels,   and   are    probably    respiratory  in    function.  thonL'h 
the  presence   of  uematocysts  renders   it  probable  tliat  they 
are    also    protective—an  idea  which    is    confirmed  by   their 


CHIATE        OrifiTlIO. 
BRANCH  (.dOolid). 


S 


316 


INVERTEBRATE  MORPHOLOGY. 


usually  brilliant  coloration.  The  foot  in  the  pelagic  PhyU 
lirhoe  has  entirely  disappeared,  but  is  usually  elongated  and 
provided  with  a  broad  flat  surface,  in  accordance  with  the 
creeping  habits  of  the  Nudibranchs.  Parapodial  folds,  such 
as  occur  in  the  Tectibranchs,  are  nevc.  developed. 


l\ 


3.  Order  Fulmonata. 

The  Pulmonates  differ  from  all  the  other  groups  of  Gas> 
teropods  in  that  they  are,  with  the  exception  of  a  single  genus^ 
Onchidium,  either  terrestrial  or  aquatic ;  and  in  adaptation  to 
this  assumed  habit  certain  well-defined  changes  have  occurred. 
In  some  genera,  more  especially  the  aquatic  forms,  such  as 
Limncea,  Physa,  and  Planorbis,  the  visceral  hump  has  its  typi- 
cal  Gasteropod  development,  and  is  spirally  coiled;  but  in 
many  terrestrial  forms,  such  as  Umax  (Fig.  142,  A),  Arion, 

and  Vaginula,  it  is  low  and  elon- 
gated parallel  to  the  long  axis 
of  the  foot  with  which  it  is 
fused.  The  mantle  is  in  all 
forms  well  developed,  but  pre- 
sents the  peculiarity  that  it  is 
fused  by  its  edges  to  tlie  body- 
wall  except  at  one  point  upon 
the  right  side,  where  an  open- 
ing is  left  by  which  the  (other- 
wise com[)letely-cIoHed  mantle- 
cavity  communicates  with  the 
exterior  and  through  which  air 
may  be  taken  into  the  cavity.  The  position  of  the  mantle- 
cavity,  when  not  interfered  with  by  secondary  changes,  is 
ui)on  the  right  side  of  the  body  and  somewhat  in  front  of 
the  visceral  hum]i  when  this  is  present.  A  spirally-coiled 
shell  is  present  in  all  forms  in  which  the  visceral  hump 
is  well  developed,  as  in  Limnim,  J'hysc,  /Mix  (Fig.  142,  //), 
and  PlamrHs,  but  in  the  elongated  terrestrial  forms  a 
rudimentatif)n  of  the  shell  accom])aiiies  the  diminution  of 
the  visceral  hump.  'J'hus  in  Dundebardia,  in  which  only 
a  slight  truce  of  the  hump  j)ersists,  the  shell  has   become 


Fio.  142. — A,  Liinax  VKirimus ;  B, 
Helix  (after  Howes). 


TYPE  MOLLUSC  A. 


317 


quite  small,  though  still  showing  plainly  a  spiral  form  ;  but  in 
Limax  it  is  represented  only  by  a  partially  calcified  plate,  im- 
bedded in  the  roof  of  the  mantle-cavity  by  the  closure  over 
it  of  a  fold  of  the  mantle.  In  Avion  only  a  few  isolated  parti- 
cles of  carbonate  of  lime  persist,  while  in  Vaginula  and  Onchi- 
dium  all  trace  of  it  has  disappeared. 

A  marked  characteristic  of  the  Pulmonata  is  found  in  the 
character  of  their  respiratory  organ.  A  ctenidium  is  entirely 
wanting,  the  culy  trace  of  its  existence  being  the  occurrence 
in  some  of  the  aquatic  forms  {Limncea,  Physa,  etc.),  of  an  os- 
phradium  near  the  mantle-pore.  Its  place  is  taken  by  the 
roof  of  the  mantle-cavity,  which  receives  a  rich  vascular  net- 
work and  functions  as  a  lung,  the  mantle-cavity  containing 
air  which  can  be  renewed  through  the  mantle-pore.  The 
heart  is  situated  far  back  in  the  mantle-cavity,  its  auricle 
lying  in  front  of  the  ventricle  and  receiving  the  blood  from 
the  more  anteriorly-situated  lung,  so  that  the  relation  of  the 
respiratory  organ  to  the  heart  is  the  same  as  obtains  in  the 
Piosobranchs.  In    tJ<e    immediate    neighborhood   of   the 

heart  lies  the  single  nephridium,  opening  into  the  mantle- 
cavity  or  else  into  the  terminal  portion  of  the  rectum  {Helix), 
...is  structure  opening  on  the  right  side  of  the  body  in  close 
proximity  to  the  mantle-pore. 

Like  the  Opisthobranchs,  the  Pulmonates  present  an 
orthoneurous  arrangement  of  the  pleuro-visceral  connectives  ; 
but  here  also  the  absence  of  a  crossing  of  the  nerve-cords  is 
probably  a  secondary  condition,  dejiending  on  the  concentra- 
tion of  the  various  ganglia  to  a  compact  mass,  since  in  a  South 
American  form,  ('hilina,  in  which  the  concentration  of  the  gan- 
glia has  not  progressed  as  far  as  usual,  a  chiastoneurism  is 
apparent. 

Special  visual  organs  are  invariably  present  with  the  struct- 
uie  which  has  already  been  described.  In  some  forms  they 
are  situated,  as  in  the  Prosobranchs,  at  the  bases  of  the  ten- 
tacles ;  while  in  others  they  are  found  at  the  tips  of  these 
structures — the  Pulmonates  being  divisible,  according  to  the 
situation  of  the  eyes,  into  the  Ba^ommatophora,  including  such 
forms  as  Limna'U,  I'liym,  I'hmorbis,  and  in  general  the  aqua- 


318 


INVERTEBHA  TE  MORPHOLOO  T. 


I 


tic  forms,  and  the  Stylommatojahora,  which  includes  the  ter- 
restrial forms,  and  OncUdium. 

This  last  genus  in  addition  to  the  usual  eyes  borne  upon  the  tentacles 
is  in  some  species  further  provided  with  a  number  of  eyes  situated  upon 
the  back  and  differing  from  the  typical  eye  in  the  arrangement  of  the  retinal 
cells.  As  has  been  seen,  the  optic  nerve  in  typical  eyes  on  entering  the  eye 
spreads  out  in  a  layer  to  form  the  retina,  tiie  terminal  optic  cells  being 
situated  on  that  sur*"'  ..  -  -.i  ihc  retina  which  is  turned  towards  the  light. 
Tlie  dorsal  eyes  ol  ■  •  iain,  however,  present  a  somewhat  different 
arrangement,  the  ceU .  .  which  the  nerve-fibres  teiminate  having  their 
distal  ends  turned  away  from  the  light,  which  to  affect  them  must  pass 
through  the  layer  of  nerve-flbres  formed  by  the  spreading  out  of  the  optic 
nerve.  Compared  with  the  retina?  of  typical  eyes,  those  of  the  dorsal  eyes 
of  Onchidium  are  inverted  and  have  assumed  an  arrangement  exceedingly 
rare  in  Invertebrates,  but  typical  for  the  lateral  eyes  of  the  Vertebrata. 

Otocysts  are  always  present,  and  the  tentacles  borne  by  the 
head  are  probably  tactile  in  function.  In  the  Stylommatoph- 
orous  Pulnionates  there  are  in  some  cases  (Helix)  two  pairs 
of  such  tentacles,  the  eyes  being  situated  upon  the  posterior 
pair,  both  pairs  furthermore  being  capable  of  being  invagi- 
nated  for  protection  into  the  body-cavity,  a  peculiarity  not 
presented  by  the  tentacles  of  the  Basommatophora.  As 
stated  above,  the  osphradium  is  represented  in  certain  aquatic 
forms,  but  in  tlio  Stylommatophora  it  has  disappeared  with 
the  suppression  of  the  ctenidium. 

The  Pulmonata  are  hermaphrodite,  the  epithelium  of  the 
reproductive  gland  (Fig.  143,  hg)  differentiating  into  both 
spermatozoa  and  ova,  there  being  no  localization  of  the  for- 
mation of  either  one  or  the  other  in  a  special  portion  of  the 
j^laud,  as  happens  in  some  Opisthobranchs.  In  the  Basom- 
matophora and  certain  terrestrial  Pulnionates,  such  as  Vagi- 
riula  and  Onchidium,  the  common  duct  (hd)  for  the  spermatozoa 
and  ova  divides  and  passes  to  the  exterior  by  two  distinct 
and  separate  apertures.  Thus  in  Limncea  the  hermaphro- 
dite duct  shortly  after  leaving  the  gland  divides,  and  into  oue 
of  the  branches  immediately  after  the  division  there  opens  a 
well-developed  albuminiparous  gland  (<f?\  and  it  then  becomes 
somewhat  folded,  forming  what  is  termed  the   uterus   (ut). 

^  jv-uvi    tiiio   nlruvvuic    tiic  viuct,  tlO  w  iviJUWLt  JIS  tllG  OVICUmI  (r>rf), 

receives  the  duct  of  a  uidamental  gland  and  dilates  into  a 


TYPE  MOLLUSC  A. 


319 


large  pyriform  structure,  which  tapers  somewhat  to  form  a 
vagina  opening  to  the  exterior  and  receives  a  duct  from  the 
receptaculum  seminis.  The  vas  deferens  {vd)  shortly  after 
Its  separation  from  the  hermaphrodite  duct  dilates  into  a 
glandular  structure,  the  prostate  gland,  from  which  the  nar- 
row duct  passes  onward  to  terminate  in  an  enlarged  penis- 
sheath  (^e)  which  contains  the 
muscular  protrusible  penis 
and  opens  to  the  exterior 
quite  independent  of  the 
opening  of  the  vagina. 

In    the    majority    of    the 
Stylommatophora  (Fig.   143), 
however,  the  two  ducts  open 
iuto  a  common  atrium  so  that 
only  one  genital  orifice  occurs, 
as  in   some    of  the  Opistho- 
branchs  (see  p.  312).     Other- 
wise the  arrangement  is  simi- 
lar   to   what    has    been    de- 
scribed for    the    Basommato- 
phora,    except   that    in   some 
forms,    as  Helix,   one  or   two 
additional     accessory     struc- 
tures are   added.     Thus    the 
atrium     has     communicating 
with  it  a  sac  which  contains 
a   sharp   calcareous  rod,  the 
"dart,"    which    serves    as    a 
stimulus    during    copulation, 
being  plunged  into  the  body 
of  the  other  party  to  the  act ; 
and  again  just  at  the  point  where  the  vas  deferens  opens 
nto  the  penis  it  has   communicating  with  it  an   elongated 
tubular  structure,  the  "flagellum,"  which  perhaps  furnishes 
the  material  of  which  the  capsule  of  the  spermatophores  is 
composed. 

Development  and  Affinities  of  the  Gmteropods.-— The  devel- 
opmeut  of  the  Gasteropods  is  made  interesting  on  account  of 


Fig.  143.— Reproductive  Organs  of 

Limax  maximus  (after  Simroth). 
al  =  alljumluipuiousglaud. 
hfi  =  hemiapLrodite  duct. 
hg  =  hermaphrodite  gland. 
U  =■  ligament. 
od  =  oviduct. 
pe  =  penis-sheath. 
?•«  =  receptaculum  seminis. 
ut  ~  uterus. 
vd  =  vas  deferens. 
V8  =  vesicula  semiualis. 


3 


„™«„.>»_ 


II 


11 


320 


INVERTEBRATE  MORPHOLOGY. 


the  occurrence  in  the  majority  of  forms  of  a  larva  knowu  as 
the  Veliger  (Fig.  144)  which  presents  many  interesting  affin- 
ities to  the  Annelid  Trochophore.  In  the  early  stages  of  de- 
velopment the  embryo  is  strictly 
bilateral,  with  the  mouth  and 
anus  at  the  extremities  of  the 
longitudinal  axis.  Upon  the  dor- 
sal surface  posteriorly  is  a  de- 
pression lined  with  columnar  cells 
which  secrete  the  larval  shell  (Sh), 
and  in  front  of  this  is  an  area 
enclosed  by  two  rows  of  cells 
bearing  stout  cilia  and  forming 
the  velum  (F).  This  band  of 
cilia  is  prseoral  (Pro)  in  posxfciou, 
and  in  addition  to  it  a  second 
band  of  smaller  cilia  is  to  be 
found  which  passes  ventrally  to 
the  mouth  and  constitutes  a  post- 
oral  band  (Poo),  the  groove  be- 
tween it  and  the  prseoral  baud 
being  occupied  by  the  adoral  cilia.  On  the  ventral  surface 
is  found  a  prominence  which  represents  the  foot. 

In  later  stages  the  lateral  edges  of  the  velum  are  drawn 
out  so  as  to  form  a  broad  lobe,  sometimes  divided  into  two 
arms,  projecting  on  each  side  of  the  head ;  the  prseoral  and 
postoral  bands  of  cilia  extending  round  the  margin  of  the 
fold,  not,  however,  completely  enclosing  the  velar  area,  but  re- 
maining oi)en  on  the  dorsal  surface.  The  shell  area  increases 
markedly  in  size,  the  shell  becoming  spirally  coiled,  the  vis- 
ceral hump  which  develops  in  the  shell  area  likewise  assuni- 
iug  the  coiled  form.  At  the  margins  of  the  shell  area  a  fold 
appears,  the  rudiment  of  the  mantle,  which  gradually  increases 
in  size  as  the  shell  area  extends,  and  at  the  same  time  the 
anus  becomes  rotated  forwards  from  its  original  terminal  posi- 
tion along  the  right  side  of  the  body  to  a  greater  or  less  ex- 
tent. As  these  changes  i)rogress,  the  embryo  gradually  ap- 
proaches more  and  more  to  tlio  auuit  form,  uinering  from  it 
mainly  in  the  existence  of  the  velum,  by  means  of  which  it 


Fw.  144.— Vkligek  Lauva. 

F=  foot. 
M  =  moutb. 
Oc  =  eye. 
Poo  =  postoral  band  of  cilia. 
Pro  -  prsooral  band  of  cilia. 
8h  =  shell. 
T  =  tentacle. 
V  =  velum. 


TYPE  MOLLUSCA. 


321 


leads  a  free-swimming  pelagic  existence,  assuming  the  adult 
habit  only  after  a  further  growth  which  is  accompanied  by  a 
reduction  of  the  velum. 

Such  a  Veliger  larva  occurs  in  the  life-history  of  the  majority  of  the 
Gasteropoda,  though,  as  might  be  expected,  it  undergoes  certain  modifica- 
tions more  especially  in  terrestrial  forms,  though  even  in  these  there  are 
ample  indications  of  its  existence.  Indeed  the  Veliger  is  so  frequent  in  its. 
occurrence  that  the  conclusion  is  almost  unavoidable  that  it  has  an  ances- 
tral significance  and  represents  in  a  more  or  less  modified  condition  a 
primitive  form  from  which  the  Mollusca  have  descended.  A  comparison  of 
the  Veliger  with  the  Annelid  Trochophore  brings  out,  as  already  men- 
tioned, numerous  similarities.  These  are  especially  noticeable  in  the  ar- 
rangement of  the  ciliary  bands,  which  resemble  those  of  the  Trochophore 
part  for  part,  even  to  the  dorsal  break  in  their  continuity.  It  is  difficult 
to  believe  that  such  marked  similarities  should  have  been  acquired  inde- 
pendently in  the  larva?  of  two  different  g.oups  of  animals  and  Lave  become 
so  characteristic,  a  difficulty  rendered  all  the  greater  by  the  occurrence  of 
other  points  of  simihirity,  such  as  the  development  of  the  mesoderm,  in 
some  forms  at  least,  from  a  pair  of  mesoblasts  situated  at  the  posterior 
extremity  of  the  blastocoel ;  the  existence  of  a  thickening  of  the  ectoderm 
in  the  centre  of  the  velar  area  in  some  forms,  corresponding  to  the  apical 
plate  of  the  Trocophore  ;  and  the  occurrence  of  a  larval  excretory  organ  or 
uephridium  in  some  Veligers  which  may  be  compared  to  the  larval  ne- 
phridium  or  head-kidney  of  the  Trochophore.  The  probable  significance  of 
tills  larval  form  will  be  more  suitably  discussed  at  the  conclusion  of  this 
chapter  ;  it  remains  to  be  said  here  regarding  it  that  the  occurrence  among 
the  Pteropods  of  la.vae  with  several  bands  of  cilia  surrounding  the  visceral 
hump  is  probably  to  be  explained  as  a  secondary  adaptation,  just  as  the 
niesotrochal  Annelid  larvae  are  probably  secondary  modifications  of  a  Tro- 
chopliore. 

As  regards  the  relationships  of  the  various  groups  of  Gasteropoda 
among  themselves,  there  is  little  doubt  but  that  the  Diotocardiate  Proso- 
hraiiehs  are,  on  the  whole,  the  most  primitive  of  all  the  groups  and  stand 
nearest  to  tlie  Amphineura,  and  from  them  the  Monotocardia  iiave  devel- 
oped. The  Opisthobranchs  and  Pulraonates  are  apparently  closely  re- 
lated, tlie  latter  group  having  been  derived  from  Tectibranchiate  ancestors 
sdinewhat  more  generalized  probably  than  any  Opisthobranch  now  living. 
The  orthoneurous  character  of  the  nervous  system  and  the  structure  of  tl<o 
reproductive  system  in  the  two  groups  indicates  their  affinity,  and  it  seems 
probable  that  the  Pulmonates  are  to  be  regarded  as  Opisthobranchs  which 
have  accommodated  themselves  at  first  to  an  amphibious  life,  somewhat 
similar  to  that  now  led  by  Onehidium,  and  later  to  one  purely  terrestrial, 
at  the  same  time  differentiating  an  or£ra,n  for  .aerial  resnirrvtion,  Sucli  an. 
origin  would  imply  that  the  aquatic  species  have  secondarily  taken  to  fresh 
water  as  a  habitat,  having  originally  been  terrestrial,  an  idea  whicli  oa 


E3 


1 


322 


INVERTEBRATE  MORPHOLOGY. 


u  priori  grounds  seems  improbable  ;  but  there  seems  to  be  no  good  reason, 
if  the  aquatic  forms  are  derived  directly  from  marine  ancestors,  why  their 
ctenidia  should  have  become  replaced  by  a  lung,  since  in  the  aquatic  Pro- 
sobranch  Paladina  the  ctenidium  is  still  retained.  On  the  other  hand,  it 
may  be  again  mentioned  that  the  terrestrial  Prosobranchs  such  as  Cydu- 
stoma,  Acicula,  etc. ,  have  lost  their  ctenidium  and  resemble  a  Pulmonale 
in  their  mode  of  respiration. 


III.  Class  Scafhofoda. 

The  class  ScapLopoda  coutaius  a  small  number  of  closely- 
related  genera  of  marine  Mollusca,  Dentalium,  Siphonodenta- 
Uum,  Cadulus,  etc.,  living  imbedded  in  the  sand  in  depths  of 
from  10  to  100  fathoms  and  possessing  but  slight  poweis  of 
locomotion.  They  resemble  the  Gasteropoda  in  possessing  a 
visceral  hump  which  is  relatively  enormously  elongated  but 
does  not  undergo  a  spiral  twisting,  nor  has  it  fallen  over  to 
the  right  or  left  side  of  the  body.  Consequently  the  Scaph- 
opods  are  bilaterally  symmetrical  and  stand  in  marked  con- 
trast in  this  respect  to  the  Gasteropods. 

The  mantle-folds  are  two  in  number,  arising  from  the 
iintorior  surface  of  the  visceral  hump  and  extending  around 
the  body  so  as  to  completely  enclose  it,  meeting  posteriorly 
and  fusing  together,  except  for  a  short  extent,  dorsally  and 
ventrally,  and  forming  thus  a  tube  to  the  anterior  wall  of 
"which  the  body  is  as  it  were  attached.  This  tube  is  open  at 
either  eiid,  the  ventral  opening  being  somewhat  larger  than 
the  dorsal  one,  and  the  whole  is  enclosed  within  a  tubular 
shell  (Fig.  145,  sh)  whose  shape  corresponds  essentially  to  that 
of  the  mantle.  From  the  ventral  opening  the  foot  (/)  pro- 
jects to  a  greater  or  less  extent,  being  in  Dentalium  a  cylin- 
drical structure,  terminating  in  a  conical  process  provided 
with  two  lateral  lobes. 

The  mouth  (m)  is  situated  at  the  extremity  of  a  cylindrical 
proboscis  (not  to  be  confounded  with  the  protrusible  proboscis 
■of  a  Gasteropod)  and  is  surrounded  by  a  number  of  leallike 
tentacles,  while  at  the  base  of  the  snout  there  is  upon  eacli 
side  a  bunch  of  long  filamento'is  tentacles  (t)  capable  of  being 
pri^truded  from  the  mniith  of  the  shell  and  of  boin  ■  withdrawn 
Avithin  it.     Each  tentacle  terminates  in  a  spoon-shaped  struct- 


TYPE  M0LLU8CA. 


323 


ood  reason, 
5,  why  their 
iquatic  Pro- 
ler  hand,  it 
eh  as  Cycio- 
Pulmonate 


)f  closely. 
lionodenta- 
depths  of 
poweis  of 
ssessing  a 
}:ated  but 
n  over  to 
le  Scaph- 
n'ked  cou- 

from  the 
ig  arouud 
osteriorly 
fsally  aud 
r  wall  of 
s  open  at 
rger  than 
a  tubular 
lly  to  that 

■'  if)  Pi'o- 

n  a  cyliu- 

provided 

ylindrical 
proboscis 
)f  lealiike 
ipou  each 
B  of  being 
'ithdrawii 
ed  struct- 


mc -1 


ure  whose  concave  surface  is  furnished  with  ciliated  cells  and 
also  towards  the  margin  with  unicellular  glands.  These 
structures  have  been  supposed  to 
represent  the  ctenidia  of  the  other 
Mollusca,  but  this  view  cannot,  in  the 
present  condition  of  our  information 
concerning  their  structure  and  devel- 
opment, be  accepted  without  reser- 
vation.  The  mouth  opens  into  a 
short  oesophagus  provided  with  a 
single  chitinous  jaw-  tooth  apparently 
formed  by  a  fusion  of  two  chitinous 
masses,  and  behind  this  there  is  a 
pharynx  provided  with  a  raduia  and 
opening  posteriorly  into  the  some- 
what U-rhaped  more  or  less  convolu- 
ted intestine  (A  which  terminates  in 
the  anus  (a)  lying  in  the  mid-ventral 
Hue  behind  the  foot.  Into  the  intes- 
tine at  the  turn  of  the  U  there  open 
the  ducts  of  the  digestive  gland  (l), 
aud  into  the  posterior  portion  of  the  Fig.  145.  —  Structure  of 
intestine,  the  rectum,  there  open  in  DerUaUum  (after  letokart). 
IJentaUum  several  ducts  from  a  rectal 
f<laud  which  surrounds  this  portion 
of  the  digestive  tract  and  whose  sig- 
nificance is  quite  obscure. 

The  nervous  system  presents  the 
niajoi-ity  of  the  ganglia  characteristic 
cf  the  Gasteropoda,  and  the  pleuro- 
vis(;eral  connectives  do  not  cross  one 
another.  The  cerebral  ganglia  (ce) 
lie  at  the  base  of  the  proboscis  an- 
terior to  the  cesophagus  and  have 
closely  associated  with  them  the  pleural  ganglia,  the 
cerebro-pedal  and  pleuro-pedal  connectives  fusing  with  one 
another  to  pass  downwards  and  forwards  to  the  pedal  ganglion 
{jk)  situated  in  the  foot.  Posteriorly  in  the  vicinity  of  the 
rectum   lie   the   two   visceral   ganglia  (vi)  from  which   long 


a  =  anus. 

ce  =  cerebral  ganglion. 

/  =^  foot. 

i  =  iutesliae. 

I  =  liver. 
m  =  mouth. 
mc  =  luaiitle-cavity. 
pe  =  pedal  ganglion. 

r  =  reproductive  organ. 
rn  =  right  nephridiuni. 
s7i  =  shell. 

t  =  tentacle. 
vi  =  visceral  ganglion. 


^cao' 


I 


324 


INVERTEBRATE  MOIIPIIOLOOT. 


nerves  pass  Jorsally,  but  uo  special  parietal  gauglia  occur. 
Two  pairs  of  buccal  gauglia  are  also  preseut.  Otocjsts  are 
preseut  imbedded  in  the  foot  in  the  neighborhood  of  the 
pedal  ganglia,  but  no  other  special  organs  of  sense,  unless 
the  bunches  of  tentacles  be  considered  such,  occur. 

No  special  respiratory  organs  are  developed,  the  mantle 
probably  subserving  the  respiratory  function.  The  heart,  a 
simple  invagination  of  the  wall  of  the  pericardial  cavity,  lies 
in  the  posterior  region  of  the  body,  on  the  dorsal  surface  of 
the  intestine.  It  possesses  no  auricle,  but  receives  the  blood 
through  small  slits  in  its  walls.  There  are  no  special  blood- 
vessels, but  the  blood  circulates  through  a  series  of  sinuses 
traversing  the  body  in  various  directions. 

A  pair  of  nephridia  occurs  in  the  posterior  region  of  the 
body,  opening  to  the  exterior  by  a  pore  on  either  side  of  the 
anus,  but  a  communication  with  the  pericardial  cavity  is  said 
to  be  wanting.  However  this  may  be,  the  right  uephridinm 
{rn)  serves  for  the  exit  of  the  reproductive  elements,  though 
the  exact  method  by  which  these  latter  make  their  way  into 
the  duct  is  unknown.  Between  each  nephridial  pore  and  the 
anus  there  is  a  pore  which  seems  to  be  the  opening  of  a  short 
tube  which  communicates  directly  with  the  schizocoelic  sinus 
surrounding  the  terminal  portion  of  the  intestine  and  places 
it  in  communication  with  the  surrounding  water,  a  peculiar 
arrangement  which  recalls  the  dorsal  pores  of  the  oligo- 
chsetoiis  Annelids.  The  Scaphopods  are  bisexual,  and  the 
reproductive  organs,  ovaries  or  testes,  are  single,  consisting  of 
long  completely  closed  sacs  with  lateral  diverticula,  lying 
along  the  posterior  wall  of  the  visceral  hump.  As  already 
stated,  the  reproductive  elements  after  the  rupture  of  the  wall 
of  the  reproductive  gland  make  their  way  to  the  exterior 
through  the  right  nephridium. 

Develop metit  and  Affinities  of  the  Scaphopoda. — The  larva  of  Btiita- 
Hum,  though  presenting  considerable  resemblance  to  the  Trochopliore, 
differs  from  it  nevertheless  in  several  points  of  detail.  It  possesses  ii  dis- 
tinct apical  tuft  of  cilia  and  the  prototroch  is  present,  though  represented 
by  three  or  more  circles  of  cilia-bearing  cells.  The  mantle-folds  develoi)  ;it 
a  relatively  early  stage  as  two  lateral  folds,  quite  separate  along  the  ventral 
line,  the  fusion  characteristic  of  the  adult  only  uppcaiiug  later.  It  is  this 
early  development  of  the  mantle-lobes  and  the  multiplication  of  the  proto- 


TYPE  MOLL  use  A. 


835 


ti'och  bauds  wliicli  obscure  the  Trocliopliore  diameters,  a  still  earlier  larva 
presenting  greater  similarities  to  the  annelid  larva. 

By  the  earlier  writers  the  Scaphophods  were  considered  more  closely 
related  to  the  Pelecypoda  than  to  the  other  MoUuscan  groups,  this  relation- 
ship being  indicated  more  especially  by  the  symraetrJcal  form,  the  apparent 
lateral  arrangement  of  the  mantle-folds  and  the  absence  of  eyes.  Un  the 
other  hand,  there  are  a  large  number  of  differences  between  the  members 
of  the  two  groups,  as  for  instance  tiie  univalve  ch«»racter  of  the  shell,  and 
especially  the  occurrence  of  a  radula  and  jaw.    This  latter  feature  suggests 


FrC.  146.  -DiAGKAMS  TO  SHOW  THE  OrfOIN  OP  THE  SCAPHOPODS  PROM  A   Fis- 

aureUa-hk*i  Anckstok  (after  Plate). 

ct  =  cteiiitlium.  go  =  reproductive  organ. 

/  =  foot.  m  =  mouth. 

ah  =  shell, 

the  Gasteropods,  and  it  seems  most  probable  that  it  is  to  this  group  that 
the  Scaphopods  should  be  considered  as  related.  They  must,  however,  be 
referred  to  the  more  primitive  Gasteropods,  those  in  which  the  rotation  of 
the  mantle-chamber  had  not  occurred.  An  elongation  of  the  dorsal  hump 
ot  a  FissureUa-Viko  ancestor  unaccompanied  by  a  twisting  to  one  side,  as 
represented  in  Fig.  146,  would  bring  about  a  condition  from  which  it  does 
not  seem  a  great  step  to  reach  the  Scaphopods. 

Among  recent  Gasteropods  it  is  with  the  Diotocardiates  that  the 
Scaphopods  seem  to  be  most  affiliated,  and,  as  we  shall  later  see,  it  is  from 
tlie  primitive  members  of  this  order  that  the  Pelecypods  have  probably 
been  derived,  and  thus  any  similarities  which  may  exist  between  the 
Scaphopods  and  Pelecypods  is  readily  explicable  on  the  basis  of  a  similar 
ancestry,  both  groups  being  derived  from  Prosobranch-like  forms.  The 
absence  of  a  larva  corresponding  closely  to  the  Gasteropod  Veliger  would 
si'ern  to  oppose  such  a  view,  but  it  must  be  remembered  that  the  Veliger  is 
eliaracteristic  only  of  the  more  highly-differentiated  Prosobranchs— such 


326 


INVER TEBRA  TE  MORPHOLOQ  T. 


forms  as  Patella,  for  instance,  having  a  larva  destitute  of  some  of  the 
more  characteristic  Veliger  features  and  more  closely  resembling  thet 
Annelid  Trochophore  and  the  Scaphopod  larva. 


IV.  Class  Pelecypoda. 

The  class  Pelecypoda,  also  known  as  the  Zamellibranchiay 
contains  a  number  of  fresh- water  genera,  though  the  majority 
are  marine,  and  all  its  members  retain  the  primitive  bilateral 
symmetry  of  form,  no  visceral  hump  being  developed.  The 
body  is  more  or  less  laterally  compressed  and  two  large 
mantle-folds  (Fig.  149,  m)  are  developed,  arising  one  on  each 
side  a  short  distance  ventrad  of  the  dorsal  mid-line  and  extend- 
ing downward  so  as  to  meet  below.  They  thus  enclose  a  wide 
space,  the  mantle-cavity,  between  their  inner  surfaces  and  the 
body-wall,  within  which  lie  the  ctenidia  (Fig.  148,  ct)  and  the 
foot  (/)).  Upon  the  mantle-edge  in  many  forms  tentacles, 
papillae,  glands,  and  eyes  are  developed,  and  in  many  cases 
the  edges  of  the  two  lobes  may  fuse  more  or  less  completely, 
openings  being,  however,  left  for  the  entrance  and  exit  of 
water  into  the  mantle-cavity,  and  also  for  the  protrusion  of 
the  foot.  All  gradations  of  fusion  are  represented :  thus  in 
Nucida,  Ostrt'K,  etc.,  there  is  no  fusion  whatever;  in  Unio 
(Fig.  149)  and  other  forms  the  posterior  edges  of  the  mantle- 
folds  are  modified,  so  that  while  the  edges  of  the  folds  are  in 
contact  throughout  the  greater  portion  of  their  extent  two 
openings  are  left,  through  the  uppermost  of  which,  the  exha- 
lent  opening  {eo),  water  carrying  with  it  the  excreta  and  the 
reproductive  elements  finds  an  exit,  while  through  the  lower 
one,  the  iuhalent  opening  (/o),  fresh  water  passes  in ;  in  the 
next  gradation  the  point  of  separation  between  these  two 
openings,  which  in  Umo  was  simply  formed  by  the  contact  (  f 
the  mantle-edges,  becomes  permanent  V)y  the  fusion  of  these 
latter  parts,  and  a  further  stage,  seen  iu  Venus  for  exam])le, 
is  formed  by  the  fusion  of  the  mantle-edges  ventral  to  the 
branchial  opening,  a  fusion  which  may  extend  forward  a  con- 
siderable distance.  In  this  last  condition  there  are  three 
openings  which  place  the  manth^-cavity  in  communication 
with  the  exterior,  one  anterior,  through  which  the  foot  is  pro- 


TYPE  MOLLUSC  A. 


327 


le  of  the 
bling  thft 


ranchia,. 
laajority 
jilateral 
d.  The 
'o  large 
on  each 
[  extend- 
e  a  wide 
and  the 
and  the 
jntacles, 
ly  cases 
ipletely, 
exit  of 
usion  of 
thus  in 
in  Unio 
mantle- 
Is  are  in 
;ent  two 
he  exha- 
and  the 
le  lower 
;  in  the 
ese  two 
nitact  (  f 
of  these 
3xam])Ie, 
,1  to  the 
'd  a  con- 
re  three 
inication 
>t  is  pro- 


traded,  and  two  posterior,  the  branchial  and  anal  openings. 
The  mantle  around  these  latter  frequently  becomes  prolonged 
so  that  two  tubes,  or  siphons  as  they  are  termed,  are  formed, 
sometimes  in  contact  with  one  anotlier  (Pholas),  sometimes 
quite  separate  (Fe/iws),  sometimes  capable  of  retraction  within 
the  shell,  sometimes  so  large  as  to  be  incapable  of  retraction 
(Mya). 


Fig.  147.—^,  Mya  nrenaria  with  the  siphons  slightly  expanded;  B,  inner  sur- 

face  of  the  riglit  valve  of  the  shell  of  Mi/<i. 
aa  =  impression  of  anterior  ad-  pa  =  impression  of  posterior  -A- 

dnctor  muscle.  d„ctor  muscle. 

I  =  ligament.  pi  =  p,iiii,ii  Hue. 

wi  =  mantle  edge.  «  =  siphon. 

^  =  '^'^"'"  »i  =  si|)h()nal  impression. 

In  conformity  with  the  form  of  the  mantle-lobes  the  shell 
consists  of  two  simihir  portions  or  valves,  lying  on  the  sides 
of  the  body  and  united  along  the  dor.sal  mid-line  by  a  hinge. 
The  hinge  is  formed  by  a  ligament,  as  it  is  termed,  which  is 
really  a  portion  of  the  shell  substance,  and  consists  of  an 
external  portion  continuous  with  the  <'))idernns  of  tlio  shell 
and  an  internal  elastic  portion,  frequently  calcified  to  a  cer- 
tain extent,  and  continuous  with  the  middle  layer  (prismatic 
-aypr^  a,  tno  ^iieli.  tr  tu-u  at  rest  the  two  valves  of  the  sheii 
are  kept  apart  along  the  ventral  lino  by  the  elasticity  of  the 
hinge-ligament,  and  it  is  only  by  the  a[)plicati()n  of  force  that 


I'l 


:^i 


328 


INVERTEBRATE  MORPHOLOOT. 


the  two  valves  can  be  brought  together,  the  ligament  being 
then  compressed.     The  hinge  is  frequently  complicated  by 
the  development  of  tooth-like  processes  and  corresponding 
sockets  so  that  the  two  valves  may  be  firmly  locked  together. 
Upon  the  inner  surface  of  the  valves  are  certain  impressions 
produced  by  the  softer  parts  and  of  considerable  value   in 
systematic  conchology.     A  short  distance  from  the  margin  of 
each  valve  and  parallel  to   it  is  a  distinct  line,  the  pallial 
impression  (Fig.  147,  pi),  produced  by  the  attachment  of  the 
muscle-fibres  which  bind  the  mantle-lobes  to  tlie  shell.     In 
some  forms,  such  as  Anodon,  this  pallial  line  follows  the  shell 
margin  throughout  its  entire   course,  but  in   those   genera 
which   possess  well-developed   and   retractile   siphons  it  is 
deeply  incurved  in  the  posterior  portion  of  its  course.     Other 
markings  of  the  shells  are  produced  by   the  insertion  into 
them  of  a  number  of  muscles.     The  largest  and  most  import- 
ant of  these  are  the  adductor  muscles  of  the  shell  (aa),  large 
muscles  passing  from  one  valve  to  the  other,  by  their  contrac- 
tion overcoming  the  elasticity  of  the  hiuge-ligameut  and  cIok- 
iug  the  shell.     In  the  majority  of  forms  there  are  two  such 
muscles,  situated  towards  the  anterior  and  posterior  jiortion 
of  the  body,  but  not  unfrequently,  as  in  Ostrea  and   /*edeu, 
but   one,  corresponding   to  the   i)<)sterior  adductor  of  other 
forms,  is  present.     In  tlie  immediate  vicinity  of  the  adductor- 
impressions   other   smaller    muscle-impressions   are    usually 
observable,  produced  by  the  protractor  and  retractor  muscles 
of  the  foot  and  siphons. 

Although  in  the  Pelecypod  slioll  the  two  valves  aro  typieully  similur 
j.nd  syiniiR'trieal,  yet  in  a  nnnilxn'  of  cases  a  marked  dissiniilarity  is  found 
in  thdir  shape.  Thus  in  (htrea  the  valve  upon  whieh  the  animal  rests, 
usually  the  hfft  valve,  is  larj;e  an<l  concave,  whiU^  \]n\  other  is  smaller 
and  flattened,  and  a  similar  relation  is  found  in  other  forms  wliieli  hc- 
oonie  l(>mporarily  fastened  to  nx'ks,  etc.  Occasionally  acMilionid  cal- 
careous plates  are  added  to  the  usual  shell,  as  in  the  horiiiR  mollusk  7'/(f>/«.v. 
in  which  three  accessory  calcareous  plates  are  devel()i>ed  on  tlH>  dorsjd  sur- 
fi'CO  of  the  hody.  In  the  Siiip-worm,  or  Tendi),  wiiich  hores  extensively 
into  timber  and  is  in  some  eases  exeecdiiiKly  destructive,  the  true  sla^ll- 
v-vlv'.'P.  are  Terv  sniall  and  situated  at  the  anterior  end  of  i\w  body,  aJid  I  he 
mantle  projects  backwards  far  beyond  them  and  secretes  a  thin  calcareoiiv 
lube  which  lines  the  interior  of  the  passages  excavated  by  the  animal.     A 


TYPE  MOLLUSCA. 


329 


t  being 
ited  by 
jonding 
)getlier. 
'essious 
alue  in 
argin  of 

pallial 
t  of  the 
ell.  In 
lie  shell 

genera 
IS  it  is 
Other 
on  into 
iniport- 
1),  large 
contrac- 
,ud  clos- 
wo  snc'h 

portion 

:)i  other 

dduetor- 

UHUally 

nmsfU's 


lly  similar 
y  is  foil  11(1 
mill  rortts, 
is  smaller 
wliicli  hr- 
lioiial  cal- 
isk  Pltiiliin, 
iloi'sal  sur 
'xteiisivclv 
true  slicli- 
ly,  and  iIh' 
cjilcart'dii- 
iiiiniul.     A 


similar  peculiarity  is  found  in  the  Aspergillum.  Here,  too,  the  true  shell- 
valves  are  exceedingly  small  and  are  united  together  by  and  imbedded  in 
a  calcareous  tube  secreted  by  the  mantle,  which  projects  far  beyond  the 
shell  proper  and  is  fused  throughout  the  greater  portion  of  its  extent 
The  calcareous  tube  is  open  behind  for  the  passage  of  the  two  siphons' 
but  anteriorly  is  closed  by  a  perforated  plate,  the  margins  of  the  perfora- 
tions being  sometimes  prolonged  into  tubes  which  may  branch  dichoto- 
mously.  The  animal  lives  imbedded  in  the  sand,  the  posterior  ex- 
tremity of  the  shell  being  directed  upwards,  and  seems  to  have  been 
derived  from  forms  originally  possessing  a  boring  habit,  such  as  is  seen  in 
Teredo. 

The  foot  of  the  Pelecypoda  is  as  a  rule  very  simple.     lu 
the  most  primitive  members  of  the  group,  such  as  Nucula 
(Fig.  151),  it  is  a  flat  disk-like  structure,  recalling  somewhat 
the  foot  of  the  Gasteropoda,  but  more  usually  it  is  a  keel- 
shaped  structure  (Eig.  149,  p).     The  modifications  in   shape 
which  it  undergoes  are,  however,  numerous  and  it  may  even 
in  some  cases  be  almost  absent,  as  in  the  Oyster  {Ostrea),  but 
special  developments,  such  as  epipodia,  are  never  found  in 
connection   with   it.      A  "  byssus-glaud "  is  a   characteristic 
development   of  the   Pelecypod  foot,  consisting  of  a  cavity 
witli  usually  greatly  folded  walls  lying  in  the  tissues  of  the 
foot  and  connected  with  the  exterior  by  a  canal  opening  on 
the  sole  of  the  foot.     By  the  cells  lining  the  cavity  threads  of 
a  horny   consistency  are   secreted  by  means  of  which   the 
animal  is  enabled  to  fasten  itself  to  stones,  etc.,  or  even  in 
some  cases,  as  Mytilm,  to  move  about  in  the  absence  of  a 
uell-developed  foot,  throwing  out  byssus  filaments,  attaching 
them,  and  tiieu  drawing  itself  forward  towards  them. 

The  re8])iratory  organs  (Fig.  149,  hr)  of  the  Pelecypoda 
consist  of  a  pair  of  i)latelike  structures  situated  on  each  side  of 
the  body,  and  being  attached  along  tlu'ir  doisal  margins  hang 
(lown  between  the  mantle  and  the  body-wall.  Notwithstand- 
ing their  plat(>like  forn.  they  are  moilificaticms  of  the  i)lnniose 
.'tenidium  of  the  Gasteropods.  If  the  typical  bipinnate 
eteijidium  be  imagined  tu  be  directed  i)arall(>l  to  tin*  long 
axis  of  the  body  and  the  median  axis  to  have  fused  with  the 
body-wall,  so  that  the  two  rows  of  piunie  are  bent  down  so 
as  to  lie  parallel  to  one  another,  the  simi)lest  form  of  the 
Pelecypod  ctenidium,  such  as  occurs  in  Nucula  (Fig.  151),  will 


1 


830 


INVEUTEBRATE  MOliPlIOLOGT. 


bt)  obtained.  lu  the  majority  of  forms,  however,  the  arrange- 
ment is  much  more  complicated  than  this.  Thus  in  Mytilus 
it  Avill  be  found  that  the  various  piunfo  composing  each 
plate  arc  held  together  by  a  series  of  patches  of  strong  cilia> 


^^^^ 


F/G.  148.—^,  (liftgramnifttic  section  through  Pecten,  and  B,  through  Anodon; 

C,  section  through  gill-luuicUti  of  Pecten,  iiud  D,  of  Anoilon. 
au  =  a\uicle.  "'  =  outer  lamella  of  outer  gill. 

/  =  foot.  P*^  =  pericardial  cavity. 

gf  =  gill-filament.  i'  =  P<>'«- 

iil  =  inner  lamella  of  inner  gill.  «  =  blood-sinus. 

il  =  intcrlan\ellar  juucliou,  »br  =  suprabranchial  chamber. 

ne  =  nephridium.  «'*  =  shell. 

which  interlock  forming  the  "ciliated  junctions,"  and  further- 
more the  pinnro  are  at  their  free  ends  bent  abruptly  \\\w\\ 
themselves,  those  of  the  outer  row  outwards  and  those  of  tlip 
inner  row  inwards,  so  that  each  gill-plato  is  composed  of  two 
lamellm  (Fig.  148,  A).  This  ctmdition  may  be  regarded  as  tlio 
next  step  in  the  modification,  which  is  continued  even 
further  by  the  permanent  union  of  the  outer  and  inner  linihs 


TYPE  MOLLUSCA. 


331 


of  the  pinnsB,  or  gill-fikmeuts  as  they  may  be  called,  by  hollow 
processes,  the  "  iuterlamelhir  juuctious "  (Fig.  148,  C,  il) 
A  still  greater  departure  from  the  primitive  condition 
is  found,  however,  iu  the  greater  uumber  of  existing  Pelecy- 
pods,  consisting  of  a  fusion  of  all  the  filaments  of  each  lamella 
into  a  plate  (Fig.  148,  />;,  small  openings  {p)  only  beiug  left  here 
and  there  between  adjacent  filaments;  furthermore  the  inter- 
lamellar  junctions  become  very  well  developed,  so  that  the 
two  lamelhe  of  each  gill  become  firmly  united  together  to  form 
a  plate,  containing  in  the  interior  a  cavity,  the  interlamellar 
si)ace. 

In  addition  to  these  various  modifications  which  lead  to 
tlie  formation  of  a  true  lamellate  gill,  the  edge  of  the  external 
lamella  of  the  outer  plate  fuses  with  the  inner  surface  of  the 
mantle,  and  the  internal  lamella  of  the  inner  plate  fuses  sim 
ilarly  with  the  side  of  the  foot  (Fig.  148,  H),  and  the  mantle- 
cavity  thus  becomes  divided  into  two  chambcus.    luto  the  ven- 
tral chamber  the  inhalent  siphon  opens,  and  the  water  which 
enters  by  it   passes  through  the   openings  left  between    the 
filaments  and  so  reaches  the  interlamellar  spaces  which  com- 
municate  above  with  the  dorsal  or  suprabranchial  chand)er 
{.shn,  whence  ifc  passes  to  the  exterior  through  the  exhaleut 
siphon.     In  the  region   of  the  foot  the  su]>rabvanclrfal  cham- 
ber IS  of  course  divided  into  two  portions,  one  of  which  lies 
on  each  side  of  the  base  of  the  foot,  and  eacli  of  these  is  a-ain 
divide;!  longitudinally  into  an  innar  and  an  outer  portion  by 
the  hue  attachment  of  the  gills  to  what  may  be  considered 
the  roof  of  thd  mantlo-cavity.  Behind  the  foot  the  inner  cavities 
"f  the  two  sides  unite  and  in  some  forms  open  ventrallv  into 
the  mantl,>-cavity  i.rop.-r  ;  in  others,  however,  the  inner  lamellro 
nt  the  inner  gdl-phites  fuse  with  one  anotlua-  ahu.gthe  middle 
hue  so  that  a  distinct  partition,   formed  by  the  gills,  sepa- 
rates the  suprabranchial  chamber  from  the  ventral  mantle- 
<'l'and,or  throughout  its  cmtire  length      In  a  few  forms,  such 
as  r//,v;„,/,rn<r,  the  gills  become  reduced   :o  sMuple  muscular 
partitions  perforated  by  por(>s  and  separatirg  the  two  cham- 
I'J'i's,   practically  all   indication    of    the    original    ctenidium 
chitrncterH  liuving  disaj)])Ciii(Ml. 

The  muscular  system  of  the  Pelecypoda  reaches  a  some- 


^ 


332 


INVERTEBRATE  MORPHOLOGY. 


what  extensive  development  in  connection  with  the  presence 
of  the  bivalved  shell.  The  mantle-folds  are  as  a  rule  some- 
what richly  provided  with  muscle-fibres  especially  near  the 
margin ;  and  where  siphons  are  developed  some  of  the  fibres 
are  specialized  into  retractors  for  these  organs.  For  the  closure 
of  the  shell- valves,  however,  more  extensive  muscular  bands  are 
present  which  seem,  like  the  siphonal  retractors,  to  be  special- 
ized portions  of  the  mantle  musculature.  Of  these  shell- 
adductors  there  may  be  one,  as  in  Ostrea  and  Pecten,  or  two,  as  in 
Anodon  (Fig.  149,  aa  and  pa),  which  pass  transversely  across 
the  body  from  one  shell-valve  to  the  other,  in  the  form  of 
stout  compact  muscular  bands.  In  connection  with  the  foot 
special  bands  are  also  developed  which  function  as  protrac- 
tors {pp),  retractors  {rp),  and  elevators  arranged  in  pairs  and 
extending  from  the  inner  surfaces  of  the  shell-valves  to  spread 
out  below  in  the  foot.  These  various  bundles  seem  to  cor- 
respond to  the  spindle-muscle  of  the  Gasteropods. 

The  coelom  presents  an  arrangement  similar  cO  that  of 
other  Mollusca,  both  schizocoelic  and  enterocoelic  portions 
being  distinguishable.  To  the  former  portion  belong  the 
numerous  lacunar  spaces  which  traverse  the  body  and  mantle- 
folds,  and  to  the  latter  the  pericardial  cavity  (Fig.  149,^9)  and 
the  cavity  of  the  reproductive  glands.  The  blood-vascular 
system  consists  of  a  ]'eart  provided  with  two  lateral  auricles 
and  lying  in  the  pericfi,rdium.  In  the  majority  of  forms  the  ven- 
tricle {v)  seems  to  be  traversed  by  the  terminal  portion  of  the 
digestive  tract,  a  condition  produced  by  its  having  folded  itself 
longitudinally  around  the  rectum,  and  which  recalls  what 
occurs  in  certain  Diotocardiate  Gasteropods  (see  p.  305).  This 
arrangement  does  not,  however,  obtain  in  all  forms,  some  of 
the  more  primitive  {Nwcula,  Area)  having  the  ventricle 
entirely  dorsal  to  the  intestine,  as  it  is  in  the  Amphineura,  for 
example,  while  in  a  few  others  (Ostrea)  it  has  assumed  a 
secondary  position  ventral  to  the  intestine.  From  both  the 
anterior  (ao)  and  posterior  extremities  of  the  ventricle  arteries 
arise  which,  after  branching  a  number  of  times,  pour  the  blood 
into  the  schizocoelic  lacunar  system.  Traversing  this  the 
venous  blood  is  roturucd  to  a  iongitudiiial  sinus  lying  in  tuo 
middle  line  of  the   body  just  below  the  pericardium  (Fig. 


TYPE  MOLLUSC  A. 


333 


Dresence 
ie  some- 
lear  the 
be  fibres 
}  closure 
ands  are 
!  special- 
36  sliell- 
wo,  as  in 
y  across 
form  of 
the  foot 
protrac- 
airs  aud 

0  spread 
L  to  cor- 

that  of 
portions 
ong   the 

1  mautle- 

9,  jj)  and 

vascular 

auricles 

1  the  ven- 
)n  of  the 
led  itself 
lis  what 
5).  This 
some  of 
ventricle 
eura,  for 
mmed  a 
both  the 
I  arteries 
he  blood 
this  the 
ig  in  the 
iin  (Fig. 


148,  B,  s),  whence  the  greater  portion  passes  into  the  compli- 
cated network  of  the  nephridia  aud  thence  to  a  blood-vessel, 
the  branchial  artery,  running  along  the  base  of  the  gill  of  each 
side.  After  traversing  the  gill-filaraeuts  it  becomes  arterial 
and  is  returned  to  the  branchial  veins  which  run  parallel  to 
the  branchial  arteries  and  thence  is  returned  to  the  auricles 
of  the  heart. 

The  digestive  tract  has  a  much  simpler  structure  than  in 
the  majority  of  the  Mollusca,  lacking  all  trace  of  a  radula 
and  muscular  pharynx.  On  each  side  of  the  mouth  are  two 
usually  triangular  plates,  the  so-called  labial  palps,  the  upper- 
most of  which  meet  above  the  mouth  forming  a  sort  of  upper 
lip,  while  the  lower  ones  similarly  form  a  lower  lip.  At  the 
bottom  of  the  space  separating  the  two  palps  of  each  side  is 
a  groove  which,  starting  at  the  sides  of  the  mouth,  runs  back- 
wards along  the  sides  of  the  body  to  the  gills.  This  groove 
serves  for  the  conduction  to  the  mouth  of  the  particles  of  food 
brought  into  the  mantle-cavity  by  the  action  of  the  cilia  of 
the  gills,  the  food  of  the  Pelecypods  consisting  of  diatoms 
and  other  minute  organisms  capable  of  being  captured  in  this 
manner.  The  oesophagus  opens  into  a  stomach  (Fig.  149,  5) 
which  receives  by  numerous  openings  the  secretion  of  the 
usually  voluminous  digestive  gland  (?),  the  so-called  liver,  and 
passes  posteriorly  into  the  intestine  (i),  which,  usually  in  sev- 
eral convolutions,  lies  imbedded  in  the  tissues  of  the  base  of 
the  foot.  In  the  wall  of  the  anterior  portion  of  the  intestine 
is  a  groove,  frequently  converted  into  a  canal,  which  may 
open  into  the  stomach  by  an  independent  opening ;  the  epi- 
thelium of  this  groove  or  canal  secretes  a  substance  which 
forms  a  transparent  glass-like  rod  lying  in  the  canal  and  pro. 
jecting  into  the  lumen  of  the  intestine.  The  function  of  this 
crystalline  style,  as  it  is  termed,  has  been  the  subject  of  much 
speculation,  the  most  plausible  theory  being  that  the  secre- 
tion serves  to  surround  sharp-edged  particles  of  sand  or  simi- 
hir  substances,  taken  into  the  intestine  with  food,  with  a  jelly- 
like coating  which  will  prevent  them  from  injuring  the  delicate 
walls  of  the  intestine.  Towards  its  posterior  end  the  intes- 
tine  bends  upAvards,  i.e.  dorsally,  to  a  point  in  front  of  the  heart 
aud  then  passes  directly  backwards  to  terminate  in  the  anus 


9 


I'-'-'-  ■■-    ■   ■-- 


334 


INVERTEBRATE  MORPHOLOGY. 


(a)  which  opens  iuto  the  suprabranchial  chamber  {sbr)  iu  the 
vicinity  of  the  exhalent  siphon.  The  relations  of  this  rectum 
to  the  heart  have  ah-eady  been  noted  (p.  332). 

The  nervous  system  of  the  Pelecypoda  differs  somewhat 
apparently  from  that  of  the  Gasteropods,  a  smaller  number 


P        y        ne         np' 


a  =  nnus. 
aa  —  iuiterior  adductor. 
ao  =  aoi'ta. 
hr  =  gill. 

cff  =  cerobriil  ganglion. 
eo  =  exhalent  oiilice  of  siphon. 

/  =  foot. 
go  —  genital  orifice. 

i  =  intestine. 
to  =  inhaleut  orifice  of  siphon. 

I  =  liver. 
m  =  mantle. 
ne  =  uepluidinin. 


Fig.  149. — Structcke  of  Anodon. 

np^  =  nephridial   opening   into  supra- 
branchial  chamber. 
p  z=  pericardial  cavit3^ 
pa  =  posterior  adductor. 
pfj  —  pedal  ganglion. 
pp  —  i)rotraetor  pedis. 

y  =:  reprodnctivi;  organ. 
rp  =  reUaetor  pedis. 

s  =  stomach. 
sbr  -  supiabranchiul  chamber. 
s/i  =  shell. 
V  =  venliiolc. 
vi  ~  visceral  ganglion. 


np^—  nephridial   opening  into  pericar- 
dial cavity. 

of  ganglia  being  discernible.  Above  the  fKSophagus  a  short 
distance  behind  the  mouth  is  on  either  side  a  well-marked 
ganglion  (Fig.  149,  eg)  connected  with  its  fellow  of  the  ()})po- 
site  side  by  a  transverse  commissure.  In  the  more  primitive 
forms  {NhchJo)  two  ganglia  are  found  on  either  side,  of  which 
one  evidently  corres])()nds  to  the  cerebral  and  the  other  to  the 
jiloural  g.iiiglioii  of  the  {liistcrojiods.  Where,  thei*  ore,  as  in 
the  majoritj'  of  the  Pelecypods,  but  a  single  ganglion  occurs  on 


TYPE  MOLLUSC  A, 


335 


each  side,  it  is  to  be  regarded  as  a  cerebro-pleural  ganglion. 
From  eacli  of  these  a  pedal  connective  passes  downwards  into 
the  foot  to  terminate  in  a  paired  pedal  ganglion  (p^),  and  a 
second  strong  connective  passes  backwards  on  each  side  of 
the  base  of  the  foot  to  terminate  in  a  large  ganglion  ivi\  sit- 
uated below  the  rectal  portion  of  the  intestine  and  frequently 
in  close  proximity  to  the  posterior  adductor  muscle,  and  which 
from  its  relations  is  evidently  to  be  regarded  as  representing 
both  the  parietal  and  the  visceral  ganglia  of  the  Gasteropods 
and  hence  may  be  termed  the  viscero-parietal  ganglion. 

The  sense-organs  are  of  essentially  the  same  nature  as  in 
the  Gasteropods.     Tactile  cells  exist  scattered  over  the  sur- 
face of  the  body,  and  are  especially  numerous  in  certain  lo- 
calities, as  upon  the  siphons  Avhen  these  are  present.     A  pair 
of  osphradia  are  also  present  situated  above  the  viscero-parie- 
tal ganglion   close   to   the  insertion  of  the  bases  of  the  gill- 
plates  into  the  side  of  the  body ;  and  imbedded  in  tlie  tissues 
of  the  foot,  usually  in  close  proximity  to  the  i)edal  ganglia, 
though   innervated  by  the  cerebro-])]eura],  are  a  pair  of^to' 
cysts  haviug  the  usual  structure  (see  p.  283).     In  a  number  of 
forms  paired  elevations,  evidently  of  a  sensory  nature,  have 
been  found  in  the  neighborhood   of  the  inner    ends  of  the 
siphons,  or  on  the  sides  of  the  body  a  little  in  front  of  the 
anus ;  the  function  of  these  is  doubtful,  though  it  has  been 
suggested  that  they  are  olfactory. 

Eyes  are  present  in  a  number  of  forms  and  present  various 
degrees  of  comi)lexity.     In  some  cases  a  perception  of  sudden 
variations  in  the  intensity  of  light  is  present,  as  in  the  siphons 
of  some  forms,  without  any  distinct  optic  sense-organs  being 
developed.     8eus(ny  and  pigment  cells  are  present,  howevHi*^ 
and  may  be  regarded  as  forming  a  diffuse  oi)tic  organ.     No 
eyes  occur  upon  the  head,  nor  are  tentacles  developed  in  any 
of  the  Pelecypods,  but  large  numbers  of  eyes  are  developed 
upon  the   edge  of  the  mantle  of  many  forms,  such  as  Pevten 
and  Spombjlm.     These  eyes  may  be  simple  depressions  of  the 
niautlo-margin,  the  bottom  of  the  depression  being  lined  with 
piguiented  and  sensory  cells,  a  cuticle  of  varying  thickness  cov- 
<Mii!g  this  retinal  surface.     Another  form  of  eye  (Fig.  150)  also 
occurs  upon  tentacular  processes  which  presents  aa  arrange- 


836 


INVERTEBRATE  MORPHOLOOT. 


ment  unusual  for  Invertebrates.  The  extremity  of  the  pro- 
cess is  occupied  by  a  number  of  clear  transparent  cells  which 
serve  as  a  cornea  {co)  and  which  are  continuous  with  a  zone  of 
pigmented  cells  (pgf)  analogous  to  an  iris,  and  which  pass  grad- 
ually  over  into  ordinary  ectodermal  cells.  Upon  the  inner 
surface  of  the  cornea  is  a  mass  of  transparent  cells  constitut- 
ing a  lens  (Z),  and  below  this  lies  the  sensory  portion  of  the 
eye.    The  optic  nerve  as  it  comes  towards  the  eye  branches ; 

1 
CO  ''~~ 


!,W""' 


Pig.  150.— Eye  of  Pecten  (modified  siiKhtiy  from  Pattbn). 
CO  =  cornea.  op,  op'  =  optic  nerve. 

I  =  lens.  pg  -  pigment-cells. 

la  =  blood-lacuna.  rt  =  retina. 

U  =  tapetum  luciilum. 

one  branch  (op'),  passing  to  one  side  of  the  eye,  bends  inwards 
towards  the  axis  of  the  eye  between  the  retina-cells  (rt)  aud 
the  lens.  The  sensory  portion  of  the  eye  consequently  is  in- 
verted, the  retina-cells  being  turned  away  from  the  light  which 
must  pass  through  the  fibres  of  the  optic  nerve  to  reach  them. 
Below  the  retina  and  separated  from  it  by  a  space  is  a  layer 
of  tissue,  the  Capelum  Imidum  {il),  which  serves  as  a  reflector 
and  gives  the  metallic  lustre  which  is  characteristic  of  the 


TYPE  MOLLUSC  A. 


337 


eyfi  of  Pecten,  and  below  this  again  comes  a  pigment-layer 

In  a  small  number  of  forma,  e.g.  Area,  peculiar  compound 
eyes  are  also  found  on  the  edge  of  the  mantle.  They  form 
shqht  rounded  elevations  and  consist  of  a  number  of  conical 
retinal  cells,  each  surrounded  by  a  sheath  of  six  cylindrical 
pigment-cells.  Each  of  these  g.oups  of  retinal  and  pigment 
cells  IS  known  as  an  ommatidium  and  is  separated  from  the 
adjoining  ones  by  slender  intermediate  cells,  so  that  on  sur 
face  view  the  composite  character  of  the  eye  is  very  distinct. 

The  nephridia  (Fig.  149,  ne)  of  the  Pelecypoda  are  always 
paired,  and  each  consists  of  a  tube  bent  upon  itself  lying  im- 
mediately  beneath  the  pericardial  cavity  into  which  one  of 
the  limbs  opens  {np\  while  the  other  communicates  with  the 
suprabranchial  chamber  {np\  and  so  with  the  exterior     In 
the  simplest  forms  the  entire  extent  of  both  limbs  is  glandu- 
ar,  but  in  the  majority  the  limb  which  opens  to  the  exterior 
loses  Its  glandular  character  and  surrounds  to  a  certain  ex- 
tent  the  glandular  or  proximal  limb.     In  addition  to  these 
nephridia,  frequently  known  as  the  organs  of  Bojanus    peri 
caraial  glands   are   of  common   occurrence   in   all   but  the 
simplest  Pelecypods,  and  apparently  assist  the  nephridia  in 
their  excretory  function.     They  are  known  also  as  Keber's 
organs  and   consist  either  of  outpouchings  of  the   anterior 
portion  of  the  pericardial  wall  into  the  space  between  the 
two  walls  of  the  mantle  (^mo,  Venus)  ov  of  similar  evagina- 
lons  of  the  walls  of  the  auricles  into  the  pericardial  cavity 
{Myhlm),  both  methods  of  formation  usually  being  associated. 
The  reproductive  organs  (Fig.  149,  r)  are  paired,  lying  usu- 
ally  in  the  tissue  forming  the  base  of  the  foot,  though  extend- 
mg  m  some  cases  into  the  lacunar  spaces  between  the  walls 
of  the  mantle  (Mytilus).     They  are  very  richly  branched  and 
usually  contain  in  any  one  individual   only  ova  or  sperma- 
tozoa,  as  the  case  may  be,  though  a  number  of  forms  are 
liermaphrodite-such,  for  example,  as  the  members  of  the 
genus  Cydas  and   some   species  of  the  genera   Ostrea  and 
Pecten.     The  ducts  which  convey  the  reproductive  elements 
'    1     •     \r'~'.  ~^'"  "cpuiKiia  near  tneir  proximal 

ends  in  Niu^vla  and  a  few  other  primitive  genera,  but  more 


<==:: 


n 


1 1 


838 


INVERTEBRATE  MORPIIOLOOT. 


usually  open  directly  into  tlie  suprabiauchial  chamber  quite 
near  the  opeuiugs  of  the  iiephridia  (Fig.  149,  (fo)  ;  couditious 
counectiug  these  two  extremes  are  to  be  found,  as  in  Feden, 
where  the  reproductive  ducts  communicate  v.ith  the  nephridia 
near  their  distal  ends,  and  in  Cyclas  and  (Mrea,  wliere  both 
nephridial  and  reproductive  openings  are  contained  in  a 
common  groove.  No  complex  accessory  structures  are  de- 
veloped in  connection  with  the  reproductive  organs,  as  in 
some  of  the  (iasteropods,  nor  is  there  an  intromitteut  organ 
in  the  male,  the  ova  and  spermatozoa  being  usually  extruded 
to  the  exterior,  where  fertilization  takes  place,  or  else  the  ova 
pass  from  the  suprabrauchial  chamber  into  the  iuterlamelhu' 
spaces  of  the  gill-plates  and  are  fertilized  there. 

The  structure  of  the  gills  forms  a  suitable  character  for  a 
classiticatiou  of  the  Pelecypoda. 

1.  Order  Protobranchia. 

The  gill  is  a  true  ctenidium  attached  by  its  axis  to  the 
roof  of  the  mantle-cavity  in  its  posterior  part.     In  addition  to 

P 


Fig.  151.— Hucula  nucleus  von  the  Lkft  SidJ';  aftkk  the  REiiovAL  of 
THE  Left  Siietj,  and  Left  Mantle-loue  (after  Pelse-nekk). 
aa  =  luileiior  adductor.  /  =  foot. 

ar  =  anterior  rctnictor  pedis.  g  =  reproductive  organ. 

c  =  ctenidiuui.  p  =  labial  pi\lp. 

(p  --=  levator  pedis.  pa  -  posterior  adductor. 

pr  =  posti  rior  retractor. 

tliis  primitive  feature   the  foot  has  a  creeping  surface,  tlio 
pleural  ganglia  are  not  completely  united  with  the  cerebral, 


TYPE  MOLLUSC  A. 


339 


»er  quite 
uditious 
i  Fecten, 
ephridiii 
ne  l)()tli 
ed  in  a 
are  de- 
s,  as  in 
it  organ 
ixtrnded 
s  the  ova 
lamellar 

ter  for  a 


s  to  the 
dition  to 


SMOVAL  1)1' 

gau. 
;tor. 

face,  tlio 
cerebral, 


and  the  reproductive  ducts  communicate  with  the  proximal 
portion  of  the  uephridia.  To  this  order,  which  represents  the 
most  primitive  Pelecypods,  belong  the  genera  Nucula  (Fig. 
151),  YoJdia,  and  others. 

3.  Order  Filibranchia. 

In  this  group  the  gill-filaments  have  elongated  consider- 
ably and  commenced  to  bend  upwards  at  their  ends  to  form 
the  outer  and  inner  lamellsB  {Anomia;  Mytilus,  Modiolaria,  the 
mussels ;  Area). 

3.  Order  Fseudolamellibranchia. 

In  this  the  gill-filaments  show  a  tendency  to  become 
united  together  and  the  inner  and  outer  lamellse  are  united 
{Pecten,  the  Scallop;  Ostrea,  the  Oyster). 

4.  Order  Eulamellibranchia. 

In  which  the  gill-filaments  are  united  to  form  continuous 
laraellfB.  To-  this  order  belong  the  majority  of  forms,  such 
as  the  fresh-water  mussels  Unio  and  Anodon,  the  small  fresh- 
Avater  Cyclas,  the  hard-shell  clam  or  Quahog  Venus,  the  sj^ft- 
shell  clam  Mya,  the  razor-shell  Ensatella,  the  boring-shell 
Pholas,  the  ship-worm  Teredo,  and  a  very  large  number  of 
other  genera. 

5.  Order  Septibranchia. 

A  small  group  in  which  the  gills  are  reduced  to  a  muscu- 
lar perforated  septum  dividing  the  suprabranchial  chamber 
from  the  more  ventral  mantle-chamber  (Cuspidaria). 

Development  and  Affinities  of  the  Pelecypoda. — Tlie  larva  which  is 
cliaracteristic  of  the  Pelecypods  resembles  a  Trocliophore  very  closely  in- 
deed and  may  be  described  as  a  Trochophore  provided  with  a  bivalved 
slu'U.  In  certain  forms  tiie  characteristic  ciliary  bands  may,  however, 
he  very  much  reduced,  and  in  the  fresh-water  mussels  {Unio,  Anodon) 
a  remarkable  secondary  larva  known  as  the  Olochidium  is  developed. 
Tlie  ova  undergo  their  development  in  the  interlamellar  spaces  of  the  gill 
plates,  and  the  shell-valves  assume  a  somewhat  triangular  shape,  the  apex 
usually  constituting  a  somewhat  curved  tooth,  while  smaller  teeth  may 
also  \ye  present  on  the  edges.  Each  mantle-lobe  is  provided  with  four 
tactile  papillae  on  each  side,  the  slightest  stimulation  of  which  causes  the 


' 'J^^nBl 


340 


INVERTEBRATE  MORPHOLOGY, 


tl 


i  1% 


shell-valves  to  close  with  considerable  force  and  the  teeth  to  adhere  to  any 
soft  object  they  come  in  contact  with.  By  these  arrangements  the  Glo- 
<jhidia  are  able  to  fasten  themselves  to  the  skin  of  the  fins  or  to  the  gills  of 
fishes,  where,  setting  up  an  inflammation,  they  become  enclosed  in  a  cyst 
within  which  the  organs  assume  the  adult  form,  the  embryo  assuming  a 
truly  parasitic  habit  and  drawing  nourishment  from  the  tissues  of  its  host. 
When  sufficiently  developed  the  young  mussel  makes  its  way  out  of  the 
cyst  and  assumes  a  free  mode  of  life. 

As  regards  the  affinities  of  the  Pelecypoda  there  can  be  no  doubt  that 
between  the  Protobrauchiate  forms  and  the  Diotocardiate  Gasteropods 
there  are  not  a  few  resemblances.  They  possess  a  creeping  foot,  true 
ctenidia  function  as  gills,  the  heart  is  traversed  by  the  rectum,  the  pleural 
iind  cerebral  ganglia  are  distinct,  and  the  nephridia  serve  to  transmit  the 
reproductive  elements  to  the  exterior,  all  of  which  are  also  to  be  found  in 
•certain  of  the  Diotocardiates,  such  as  Haliotis  and  Fissurella.  It  may  be 
supposed  that  the  Pelecypods  arose  from  the  Gasteropod  stem  before  the 
asymmetry  became  developed,  and  subsequently,  by  assuming  a  fixed  or 
limicolous  mode  of  life,  a  certain  amount  of  degeneration,  such  as  the  loss 
of  the  radula  and  of  tentacles  and  cephalic  eyes,  supervened.  The  plough- 
share-shaped foot  is  undoubtedly  an  adaptation  to  the  limicolous  habit, 
and  the  great  development  of  the  gills  stands  in  relation  to  their  mode  of 
obtaining  lood,  the  cilia  of  the  gills  being  responsible  for  the  production  of 
currents  sufficiently  strong  to  carry  witii  them  diatoms  And  other  small 
organisms  upon  which  the  Pelecypods  feed. 


iii^i 


V.  Class  Cephalopoda. 

The  Cephalopoda  are  in  some  respects  the  most  specialized 
of  all  the  Molhisca,  but  nevertheless  present  the  primitive 
bilateral  symmetry  and  arrangement  of  the  structures  associ- 
iited  with  the  mantle-cavity.  The  visceral  hump  is  enor- 
mously devel()i)ed  (Fig.  15'J),  so  that  the  true  anterior  and 
posterior  surfaces  of  the  body  are  very  long,  whereas  the 
ventral  surface  is  coni])aratively  short,  the  general  form  of 
the  body  being  not  uidike  tliat  of  the  Hcapho|)oda.  Unlike 
the  members  of  this  latter  class  the  Cephalopods  lead,  how- 
ever, a  somewhat  active  existence,  some,  such  as  the  Squids, 
swimming  actively  about  in  the  sea  to  which  they  are  exclu- 
sivoly  confined,  while  others,  such  as  the  Cuttlefishes,  have  a 
more  creeping  habit,  though  capable  of  swimming  freely. 
While  swimminur  the  animals  assume  a  nositiou  in  which  their 
longest  axis,  i.e.  the  dorso-ventrul  axis,  is  more  or  less  hori- 
zontal, the  true  morphological  anterior  surface  thus  beconiint; 


TYPE  MOLLUSCA, 


341 


physiologically  the  dorsal,  and  the  posterior  the  ventral  sur- 
face. In  the  following  description  the  surfaces  will  be  con- 
sidered  in  their  morphological  relations. 

The  head  is  usually  somewhat  distinctly  marked  off  from 
the  body  proper  by  a  neck  constriction  and  bears  two  usually 
remarkably-developed  and  highly-specialized  eyes.  A  pecul- 
iar  feature  of  the  Cephalopods,  and  the  one  which  has  sug- 


Fi(».  153. 


-DrAORAM  TO  SHOW  Genehai.  Pi.an  of  SruucTunE  OF  A  C'EriiA- 

LOroU  (sliKhtly  moilifled  from  Lano). 


(tn  =  amis. 

b  =  buccal  mnss. 
cie  =  cii'cum  of  stoniach. 
ct  =  clenidiiim. 

e  =  eye. 
go  =  rcpiodiiclive  organ. 

i  =  ink-bag. 
m  =  muiitle. 


mc  =  nuindf'-cavily. 
ne  =  U('|ihiiiliiiin. 

as  =  uiwoplingiis. 

8  =  stoiiiucb. 
ah  =  sbtll. 
«■  =  riiiiuol. 

t  =  tfiilaclc. 

V  =  valve  of  funnel. 


^'•'stnd  the  name  api)lied  to  the  clasH,  is  the  fusion  with  the 
li''.ul  of  a  portion  of  the  foot.  The  mouth  thus  becomes  situ- 
iitcd  at  the  bottom  of  a  funii(»l-like  (lepre.ssion,  formed  by  the 
foot,  whose  margins  are  drawn  out  into  a  number  of  tentade- 
Ix'imiig  l()l)eH  or  into  eight  or  ten  long  armlike  ])r()ceHH«'s 
(I  ig.  162,  t)  provided  with  suckers,  and  serving  as  powerful 


342 


INVERTEBRATE  MORPHOLOGY. 


orgaus  of  prelieBsion.  A  second  portion  of  the  foot  lies  in 
the  neck  region  on  the  ventral  surface  and  has  the  form  of 
two  folds  {si),  whose  edges  may  be  approximated  or  even  fused 
to  form  a  tube,  through  which  the  water  contained  in  the 
mantle-cavity  may  be  violently  expelled,  the  animal  being 
thereby  propelled  through  the  water  in  a  direction  of  their 
long  dorso-ventral  axis.  This  portion  of  the  foot  is  termed 
the^funnel  and  is  perhaps  equivalent  to  the  epipodium  of  the 
Gasteropods.  In  the  majority  of  forms  there  projects  into 
the  lumen  of  the  funnel  a  fold  (/•)  anting  from  the  body-wall 
and  termed  the  valve  of  the  funnel.  It  is  probably  homolo- 
gous with  the  posterior  portion  of  the  foot,  the  metapodium, 
of  the  Gasteropoda,  so  that  all  portions  of  the  Gasteropod 
foot  are  represented  in  the  Cephalopods,  the  propodium  and 
mesopodium  by  the  arm  bearing  porti<m,  the  metapodium  by 
the  valve  just  mentioned,  and  the  epipodium  by  the  funnel. 
In  many  forms  two  depressions  are  to  be  found  on  the  outer 
surface  of  the  funnel,  which  receive  two  corresponding  eleva- 
tions ou  the  inner  surface  of  the  mantle,  which  thus  becomes 
locked  as  it  were  to  the  funnel  during  the  expulsion  of  water 
from  the  mantle-cavity. 

The  mantle  (m)  forms  a  circular  fold  surrounding  the  vis- 
ceral hump,  but  upon  the  anterior  suiface  it  has  usually  only 
a  very  slight  development,  while  posteriorly  there  is  a  wide 
space,  the  mantle-cavity  {inc),  between  it  and  the  body-wall. 
Within  this  space  lie  the  ctenidia  {cf),  and  into  it  the  nephri- 
dia  (»e)  and  the  digestive  tract  open,  the  excreta  being  ex- 
pelled  from  it  during  the  expulsion  of  water  from  the  funnel. 
The  mantle-fold  is  rather  thick  as  a  rule,  owing  to  the  pres- 
ence in  it  of  abundant  muscle-tibres,  by  the  contraction  of 
which  the  mantle-cavity  may  be  considerably  reduced  in  si/o, 
and  fretpiently  there  is  a  special  muscular  thickening  around 
the  edge  of  the  mantle  whereby  the  mouth  of  the  cavity, 
widely  open  during  the  intaking  of  water,  nuiy  be  firmly  up. 
pressed  upon  tl.e  funnel  during  tho  expulsive  act.  In  the 
majority  of  Cephalopods  the  integument  covering  the  oui.'r 
surface  of  the  mantle  and  of  the  visceral  hump  is  provided 

.    .  .  1         .  •    -i 11..     ..J.      ,.1,  vf>»»»«i  4-/M>li<>vt>a      niviMl       OI 

witii    iibuiMiaiii    pignu3iii.-cuiir.   trr    tisioi.irtvj i--      - 

which  is  provided  with  a  muscular  arraugemeut  by  which  its 


TYPE  M0LLU8CA. 


343 


t  lies  in 

form  of 
t'eu  fused 
lI  iu  the 
al  being 

of  their 
3  termed 
im  of  the 
ects  iuto 
)ody-Avall 

homolo- 
apodiuin, 
isteropod 
Aium  and 
:nlium  by 
e  funnel, 
the  outer 
ing  eleva- 

becomes 
L  of  water 

g  the  vis- 
lally  only 
is  a  wide 
)ody-wall. 
e  nephri- 
being  ex- 
le  funnel, 
the  pres- 
•action  of 
h1  in  size, 
ig  around 
lie  cavity, 
firmly  iip- 
,.  In  the 
the  oult'r 
providod 
each  of 
which  its 


size  may  be  rapidly  diminished,  remarkable  flushes  of  color 
passing  over  the  surface  of  the  living  animal. 

Iu  the  Nautilus  (Fig.  159)  a  chambered  calcareous  shell  is 
present  having  a  rather  complicated  structure  which  will  be 
described  later,  and  iu  one  or  two  other  living  forms,  such 
as  Argonauta  and  Spirida,  an  external  shell  also  exists,  but 
in  the  majority  of  forms  the  edges  of  the  mantle  close  over 
the  shell,  which  thus  becomes  internal  and  takes  the  form  of  a 
plate  lying  along  the  anterior  surface  of  the  body,  being  some- 
times  calcareous  as  in  the  common  Cuttlefish  bone  of  com- 
merce obtained  from  the  Sepia  (Fig.  152,  sh),  or  else  chitiuous 
as  iu  the  common  Squid,  Loligo.  In  connection  with  the 
mantle  there  are  also  frequently  developed  fiulike  expansions 
with  a  cartilaginous  support  and  provided  with  muscles, 
sometimes  running  along  the  sides  of  the  visceral  hump  or 
iu  other  cases  situated  near  its  dorsal  extremity. 

The  respiratory  organs  or  ctenidia  (Fig.  154,  ct)  are  present 
as  either  one  or  two  (Nautilus)  pairs  of  pinnate  structures 
lying  iu  the  mantle-cavity.  Each  consists  of  a  central 
axis  attached  throughout  its  entire  length  to  the  body-wall, 
forming  a  rather  high  ridge  upon  it  and  containing  near  its 
outer  edge  two  blood-vessels  running  throughout  its  entire 
length.  The  vessel  nearer  the  summit  of  the  ridge  is  the 
branchial  vein  carrying  the  aerated  blood  back  to  the  body,, 
aiul  between  it  and  the  branchial  artery  is  a  cavity  or  canal 
which  communicates  with  the  mantle-cavity  between  each 
pair  of  branchial  ])innie.  These  structures  arise  from  near 
the  free  edge  of  the  axial  ridge,  but  each  is  IxMind  to  the  ridgo 
by  a  thin  triangular  meuibraue  so  that  they  possess  the  form 
(»f  lamelhe  rather  than  of  pinnie.  Near  the  line  of  attachment 
of  the  axial  ridge  to  the  body- wall  is  a  cord  of  cellular  tissue 
richly  supplied  with  blood  coming  from  the  branchial  artery, 
forming  what  is  termed  a  blood-gland,  from  which  the  blood 
is  collected  into  two  hjngitudiual  canals  which  conduct  it  back 
to  the  heart. 

The  co'loni  of  tho  Ce[)halopods  is  characterized  by  the 
great  development  of  the  pericardial  cavity  (Fig.  153,  pr), 
which  Vf-callH  ila^  couilitioii  fonn<]  iu  the  Arnphinmra,  aud 
may  perhaps  bo  bettor  termed  the  viscero-pericardial  cavity. 


If: 


lit^ 


■ 


344 


INVEliTEBHATE  MORPHOL007. 


lu  the  majority  of  forms  it  is  a  large  sac  occupying  a  con- 
siderable  portion  of  the  apex  of  the  visceral  hump  and  ex- 


F»a.  168.— Diagram  of  Body  cavity  of  /S8pi«  (after  Qrobden). 
bh  =  brauobial  heiiit.  od  =  ovitiuct. 

/  =  funnel.  '>v  -  ovary. 

(fo  =  leproductive  opening  into  coiloui.   p  =  pancreas. 
JI  =  heart.  P**  =  partition  partittlly  dividing  ca*- 

•  =  intestine.  lorn. 

lb  =  ink-bag.  pc  =  coplom. 

l  =  liver.  «  =  stonnicb. 

id  =  liver- duct.  Bh  =  shell. 

inc  -  mantle  cavity.  «  =  external  opening  of  ncphrfdium. 

N=  nepbridium.  V^  =  opening  of  nephridinin  into  cn'. 

ioni. 

teutliiig  veutraily  a  considerable  distance,   the   more  ventnil 
■pwrtion  being  incompletely  separated  from  the  more  capacionn 


^  a  cou- 
aiid  ex- 


TYPE  MOLLUSCA. 


345 


lEM). 


vidiug  ca>- 


rphridiiini. 
Ill  iiili)  <ii'- 


■d  veutiai 
'Hpacious 


tlorsal  portion  by  a  trausverse  fold  or  partial  partitiou  (pa). 
lu  Nautilus  it  is  placed  iu  direct  conimunicatiou  with  the  inau- 
tle-cavity  by  two  minute  pores,  but  in  other  forms  such  direct 
communications  do  not  occur.     With  a  ventral  prolongation 
of  the  ventral  cavity  the  nephridia  {N)  communicate,  aud  the 
walls  of  the  cavity  fold  themselves  around  the  heart  (//)  in 
the  usual  manner,  and  in  addition  also  enclose  the  branchial 
hearts  (M),  becoming  thickened  and  considerably  folded  in 
this  region  so  as  to   form  the  so-called  appendages  of  the 
brauchial  hearts,  which  are  homologous  with  the  pericardial 
glands  of  the  Lamellibranchs.     The  wall  of  the  dorsal  cavity 
is  ill  a  similar  manner  folded  over  the  viscera  present  in  that 
region,  and  more  or  less  completely  encloses  the  reproductive 
organs  {ov)  so  as  to  form  around  them  a  capsule,  sometimes 
with  muscular  walls,  into  the  cavity  of  which  the  reproduc- 
tive elements  are  shed  when  mature.     In  one  group  of  Ce- 
phalopods,  however,  the  Octopoda,  the  arrangement  departs 
slightly  from  this  owing  to  the  reduction  of  the  viscero-peri- 
cardial  cavity  to  a  number  of  comparatively  small   canals 
which  constitute  the  so-called   water  vascular  canals  of  the 
older  authors.     Three  of  these  canals  are  found  on  either  side 
of  the  body,  meeting  together  in  a  common  centre,  the  ne- 
phridia  communicating   with    one,   another    passing   to   the 
brauchial  heart  of  its  side  to  form  the  pericardial  gland,  while 
the  third  extends  dorsally  to  dilate   with  its  fellow  of  the 
opposite  side  into  the  capsule  surrounding  the  reproducti -e 
organs  (Fig.  158,  wc).      The  general  i-elationships  of  these 
canals  are  evidently  comparable   with  those  of  the  viscero- 
pericardial  cavity  of  the  majority  of  the  Cephalopods,  but 
they  differ  in  one  very  marked  peculiarity,  i.e.,  the  heart  is 
not  enclosed  within  their  lumen.     The  tubelike  condition  of 
the  cavity  is  evidently  a  secondary  condition,  and  the  exclu- 
sion of  the  heart  can  be  understood  as  a  result,  of  the  diminu- 
tion of  the  extent  of  the    avity,  when  the  manner  in  wliich  it 
is  enclosed,  as  exemplified  by  the  Holenogastres,  is  considered. 
The  schi/ocd'lic  portif)n  of  the  C(elom  tiikes  the  form  partly 
of  lacunar  spaces,  but  partly  of  blood-vessels  witli  definite 
walls.     To  a  certain  extent  the   blood   system  is  comph'telv 
closed,  an  unusual  condition  among  Mollusca  ;  well-defined 


^O 


346 


INVERTEBRATE  MORPHOLOGY. 


veins  return  the  blood  carried  by  the  arteries  to  various  por- 
tions of  the  body,  definite  capillaries  connecting  the  two  sets 
of  vessels.  A  lacunar  system  also .  exists,  however,  so  that, 
while  showing  a  much  greater  differentiation  than  the  other 
Mollusca,  the  Cephalopods  yet  retain  indications  of  the  more 
primitive  arrangement. 

Tlie  heart  consists  of  a  tubular  ventricle  (Fig.  154,  'o\ 
usually  arranged  with  its  long  axis  directed  dorso-ventrally, 


Fig.  154.— Circulatouy  Appakatus  op  /Sepi'a  (after  Hunteh  from  Owen). 

ao  =  anterior  aorta.  Iv  =  lateral  vein. 

ao'  =  abdominal  aorta.  «e  =  excretory  appendage. 

an  =  auricle.  pg  =  pericardial  glaud. 

hh  =  hrandiial  heart.  «  =  ventricle. 

et  =  ctenldium.  va  =  abdominal  vein. 

ve  =  cephalic  vein. 

though  in  the  Octopoda  it  is  transverse,  and  has  opening  into 
it  at  each  side  oue  or  two  {N<n(fihis)  auricles  {au)  which  re- 
ceive the  blood  from  the  brauchiw  (cf).  Two  piiucii)iil  aite- 
ries  arise  from  the  ventricle,  a  larger  one  running  ventrally 
{(lo),  and  a  smaller  one  whi.'li  runs  towards  the  tip  of  the 
visceral  hump  and  supplies  iho  viscera  of  that  regioit  {ao'). 
As  already  stated,  thest*  arteries  pass  into  a  fine  capillary  net- 
work fi'om  which  the  vcius  arise,  sinuses,  however,  interven- 
ing in  some  cases  in  the  roufsc  of  the  latter,  anu  possibly 
some  arterial  branches  m:iy  I'.rminate  in  such  sinuses.     The 


TYPE  MOLLUSCA. 


347 


principal  venous  trunk  is  the  .eplialic  vein  {vc),  which  lies  on 
the  posterior  side  of  the  oesophagus,  and  passing  dorsallj 
divides  into  two  branches,  the  \eiim  cavw,  with  each  of  which 
an  abdominal  vein  {m)  unites,  the  conjoined  trunk  on  each 
side  passing  into  a  contractile  dilatation,  the  branchial  heart 
(bli),  at  the  base  of  the  ctenidium  of  that  side.  The  vense  cava 
and  the  abdominal  veins  are  covered  by  a  much-folded  mass 
of  tissue,  the  venous  appendages  (ne),  which  are  portions  of 
the  uephridia  and  will  be  considered  in  the  description  of 
those  organs.  Mention  may  also  be  made  here  of  the  peri- 
cardial glands  ipg)  attached  to  the  branchial  hearts,  which 
have  already  boen  described  in  connection  with  the  viscero- 
pericardial  cavity. 

Slight  variations  from  the  arrangement  here  described 
may  be  found  in  various  forms,  of  which  the  most  important 
is  that  found  in  Nantilus,  in  which,  in  accordance  with  the 
presence  of  two  pairs  of  ctenitlia,  each  vena  cava  divides  into 
two  branches,  one  passing  to  each  ctenidium.  No  branchial 
hearts  occur,  and,  as  has  been  already  mentioned,  the  ventri- 
cle has  openinor  iuto  it  two  pairs  of  auricles  instead  of  the 
single  pair  usually  present. 

In  the  mesodermal  tissue  of  the  Cephalopods  in  various 
portions  of  the  body  there  are  developed  plates  and  nodules 
of  a  consistency  resembling  cartilage  and  like  it  consisting  of 
a  hyaline  or  partly  fibrous  matrix  through  which  numerous 
cells  with  branching  processes  are  scattered.     These  cartilagi- 
nous structures  resemble  the  tissue  which  is  developed  in  the 
pharynx  of  the  Gasteroi)ods  below   the  radula,  but  reach  a 
much  more  extensive  development  in  the  Cephalopods,  serving 
as  a  protection  for  some  of  the  more  important  organs,  and 
also  as  a  point  (Vappui  for  the  various  muscles,  and  therefore 
constituting  a  true  endoskeleton.     In  the  hhmtilus  tliere  is  but 
a  single  cartilage  which  lies  on  the  posterior  surface  of  tlie 
(Bsophagus,  being  deeply  grooved  for  the   rece})tion  of  the 
brain  and  optic  ganglia.     In  other  forms,  however,  the  carti- 
lages are  more  numerous.     There  is  a  well-developed  cephalic 
cartilage   forming   a   deeply-concave  disk  perforated  by  the 
""I "^"''  ""^'  paituiiiv  cndoHing  ine  brain,  being  also  ex- 
panded at  the  sides  and  hollowed  out  so  as  to  form  a  support 


348 


INVERTEBRATE  MORPHOLOGY. 


for  the  eves,  which  are  further  covered  by  a  pair  of  plates 
which  project  anteriorly  and  laterally  from  t)i9  anterior  margin 
of  the  disk.  At  the  base  of  the  arms  a  brachial  cartilage, 
sometimes  united  Avith  the  cephalic  mass,  is  found  which 
serves  for  the  origin  of  the  brachial  musculature,  and  further- 
more  a  nuchal  plate  is  present  lying  below  the  anterior  sur- 
face of  the  body  just  behind  the  head.  In  connection  with 
the  funnel  some  plates  and  nodules  are  developed,  the  most 
important  of  which  is  the  infundibular  cartilage  on  the  pos- 
terior (strictly  speaking  the  veutral)  surface  of  the  body  in 
the  floor  of  infundibulum,  nodules  being  found  below  the  de- 
pressions on  the  side  of  the  infundibulum  and  the  corve- 
spimding  elevatious  of  the  mantle  which  have  already  been 
described  as  interlocking  during  the  expulsion  of  water 
through  the  funnel.  Finally,  it  may  be  mentioned  that  the 
centre  of  each  tin  is  occupied  by  a  cartilaginous  plate  which 
serves  for  the  origin  of  the  muscles  which  move  the  fin. 

In  harmony  with  the  peculiar  modification  of  the  foot 
there  is  a  considerable  amount  of  dift'erentiation  of  special 
muscles  iu  the  Cephalopods,  which  pass  from  cartilage  to 
cartilage  or  from  the  shell  to  the  various  cartilages.  Leaving 
aside  the  general  musculature  of  the  mantle  and  of  the  arms, 
mention  may  be  made  of  the  three  or  four  strong  retractor 
muscles,  which  pass  from  the  shell  to  the  cephalic  cartilage 
and  are  sometimes  fused  together  to  form  a  single  strong 
muscle  which  serves  to  retract  the  head  ;  the  collaris,  which 
runs  on  either  side  of  the  neck  from  the  infundibular  cartilage 
to  be  inserted  into  the  sides  of  the  nuchal  cartilage  ;  and 
finally  the  adductors  and  depressor  of  the  funnel,  which  pass 
respectively  from  the  cephalic  cartilage  and  the  shell  to  be 
inserted  into  the  infundibular  cartilage.  Considerable  varia- 
tion is  to  be  found  in  the  arrangement  of  muscles  in  various 
forms,  but  the  tyi)ical  arrangement  may  be  regarded  as  being 
somewhat  as  described. 

Like  the  other  organs  the  digestive  system  presents  a  con- 
siderable amount  of  differentiation.  The  mouth  opens  iu  the 
centre  of  the  disk  which  bears  the  arms  or  tentaculiferous 
lobes  and  is  guarded  by  two  strong  chitinous  or  partly  calca- 
reous {Nautilm)  jaws  resembling  in  form  the  beak  of  a  parrot. 


TYPE  M0LLU80A. 


349 


w 


liicli 


It  leads  into  a  muscular  pliaryux  (Fig.  152,  h),  upou  the  floor 
of  wliicli  lies  the  characteristic  inolluscau  radula,  while  iuta 
its  cavity  the  ducts  of  oue  or  two  pairs  of  salivary  glands 
opeu,  Succeediug  the  pharyux  is  a  tubular  oesophagus  (a) 
which  iu  some  forms  is  provided  with  a  lateral  diverticulum,. 
the  crop,  and  which  terminates  below  in  the  large  pyriform 
stomach  (s).  The  intestine  leaves  the  stomach  close  to  the 
entrance  of  the  oesophagus,  and  a  pouchlike  structure,  in  some 
forms  prolonged  into  a  spiral  caecum  (ca),  is  to  be  found 
either  communicating  with  the  stomach  close  to  this  point  or 
else  opening  into  the  proximal  portion  of  the  intestine  {Nauti- 
lus). Into  this  cfficum  the  two  ducts  from  the  large  digestive 
glands,  or  so-called  liver,  open,  their  walls  being  in  the  ma- 
jority of  cases  provided  with  sacculations  arranged  in  bunches 
and  constituting  the  pancreas,  a  structure  which  in  Loligo 
(Fig.  153,  j9)  is  imbedded  in  the  thickened  walls  of  the  ducts  or 
else,  as  in  Octopus,  attached  to  the  digestive  glaud  in  the  region 
where  its  ducts  arise.  From  its  origin  in  the  stomach  the 
intestine  passes  ventrally,  the  entire  tract  having  thus  a 
V-shaped  arrangement,  and  opens  into  the  mantle-cavity  on 
the  summit  of  a  papilla  situated  a  short  distance  from  the 
dorsal  end  of  the  infundibulum.  From  each  side  of  the  anal 
papilla  a  fleshy  appendage  arises,  the  anal  valve,  which  in 
some  forms  may  be  drawn  down  so  as  to  completely  close  the 
anal  opening. 

In  connection  with  the  posterior  portion  of  the  digestive 
tract  there  is  found  in  all  Cephalopods  except  Nautilus  a  sac- 
like gland  (Fig.  152,  i)  which  secretes  a  dark  pigment  and  is 
known  as  the  ink-bag,  the  animal  discharging  the  ink  into 
the  surrounding  water  to  conceal  its  retreat  when  alarmed. 
It  arises  as  a  saclike  diverticulum  of  the  rectum  close  to  its 
termination  and,  elongating,  becomes  difl'erentiated  into  a  duct 
of  considerable  length  ()i)ening  into  the  terminal  portion  of 
the  rectum  and  closed  by  a  circular  band  of  muscle-iibres- 
which  surround  it  near  its  opening.  The  more  or  less  globu- 
lar extremity  of  the  diverticulum  becomes  differentiated  into 
(1)  a  cavity  which  serves  as  a  reservoir  for  the  inky  secretion 
mannfactui-ed  in  (2)  a  special  glandular  region,  traveracd  by  a^. 
series  of  trabecuhe  lined  hy  the  secreting  cells. 


350 


INVERTEBliA TE  MORPIIOLOG  Y. 


Tlie  uervous  system  of  the  Cephalopods  shows  a  high 
degree  of  couceiitratiou,  the  various  gauglia  beiug  more  or  less 
fused  with  one  another  to  form  a  mass  surroiindiug  the  oesc- 
phag'it^,  just  behind  the  pharyngeal  mass.  In  Nautilus  this 
muss  taiies  the  form  of  two  rugs  surrounding  the  oesophagus, 
united  in  front  but  widely  di>ergeut  behind,  and  in  which  the 
various  ganglia  are  but  indistinctly  indicated,  the  condition 
which  occurs  in  Chiton  in  this  rei-:pect  beiug  recalled.  That 
portion  of  tin  liiig  uiiich  lies  in  front  of  the  oesophagus  rep- 
resents the  cerebral  ganglia ;  the 
lateral  portions  of  the  more  ventral 
of  the  two  rings  found  on  the  pos- 
terior surface  are  the  pedal  ganglia, 
giving  rise  to  the  nerves  to  the  pedal 
lobes  and  the  infundibuluni  ;  while 
the  more  dorsal  posterior  ring  rep- 
resents the  combined  visceral,  pa- 
rietal, and  pleural  ganglia.  In  other 
forms  the  ganglia  become  more 
perfectly  marked  oil'  and  at  the  same 
time  more  concentrated.  A  cerebral 
ganglion  (Fig.  355,  c)  is  always  dis- 
tinguishable, and  with  it  are  con- 
nected pleuro-parieto-visceral  {pi 
and  v)  and  i)edal  {p  find  p')  ganglia ; 
the  latter,  however,  are  usually  divi- 
ded into  two  portions — a  more  ven- 
tral mass  {p')  which  sends  branches 
to  the  armlike  prolongations  of  the  pro-  and  mesopodium  and 
which  is  hence  termed  the  brachial  ganglion,  and  a  more  dorsal 
one  (p)  which  supplies  the  infundibulum  and  is  known  as  the 
pedal  ganglion  proper.  A  study  of  a  number  of  different 
forms  shows  clearly  that  the  brachial  ganglion  is  merely  a 
separated  portion  of  the  pedal,  and  that  the  arms  are  to  be  cou- 
sidered  portions  of  the  foot  and  are  not  cephalic  appendages. 
At  the  sides  of  tlie  cerebral  ganglia  there  are  to  be  fi>und  a 
pair  of  large  ganglia  {op)  which  stand  in  relation  to  the  eye  and 
are  termed  tlie  optic  gai'.njlia ;  they  are  undoubtedly  spe- 
cializations of  the  cerebral  ganglia,  owing  their  separate  exist- 


^^  PP'       B 

Fig   155. — Nervous  Ganglia 
OF  {A)  Loligo  and  (i?)  Octopus 
(after  Pklseneeh). 
b  —  buccal  giingliou. 
c  =  cerebml  ganglion. 
'p  =  putlul  giinglion. 
p'  =  bracl.iiil  gangliou. 
op  =  o()ti<:  ganglion. 
v  =  pltiuro  -  parielo  -  visceral 
gauglica. 


TYPE  MOLLUSC  A. 


351 


ence  to  the  remarkable  development  and  differentiation  of 
the  eye  which  is  found  in  the  majority  of  the  Cephalopods. 

A  sympathetic  system  of  nerves  is  well  developed  and  con- 
sists of  one  or  two  pairs  of  buccal  ganglia  (&)  innervating  the 
large  pharyngeal  mass  and  united  to  the  cerebral  ganglia  by 
connectives  and  giving  rise  to  a  strong  nerve  which  runs 
dorsally  along  the  oesophagus  to  end  in  a  large  gastric 
ganglion  from  which  nerves  pass  to  the  viscera.  Mention 
should  also  be  made  of  two  other  ganglia,  the  ganglia  stellata, 
which  belong  to  the  central  system  and  are  situated  in  the 
lateral  portions  of  the  mantle,  being  united  with  the  pleuro- 
visceral  ganglia  by  strong  nerves ;  they  corres])ond  probably 
with  the  parietal  ganglia  of  the  Gasteropods,  sending  branches 
to  the  tissues  of  the  mantle. 

The  special  sense-organs  are  exceedingly  well  developed, 
nnd  especially  is  this  the  case  with  the  eyes.  In  NantUus, 
Jiowever,  the  eye  (Fig.  156,  A)  stands  on  a  much  lower  grade 


Fig.  156.—^,  Eye  of  Nautilus  (modified  from  Henskn):  and  B,  of  Loligo. 
c  =  cartilage.  I  =  lens. 

CO  -  corueu.  n  -  nerve-layer. 

(J  =  layer  of  ganglion-cells.  op  =  optic  nerve  and  retinal  ganglion. 

ir  =  iris.  pg  =  pignient-hiyer. 

r  =  layer  of  rods. 

of  organization  than  that  of  the  other  Cephalopods,  con- 
sisting of  a  cup  lined  by  a  retina  composed  of  several 
layers  and  richly  supplied  with  nerves.  The  outermost 
layer  consists  of  rodlike  bodies  (r)  below  which  is  a 
layer  of  pigment   (pg),  below  which   again   lies   a   layer  of 


:anglion-celh 


\h- 1- 


No   refractive    struetur 


cs   ure. 


lowever. 


jV^-^-W 


1 


present,  the  cavity  of  the  cup  communicating  freel}^  with  the 


352 


m VERTEBRA TE  MORPHOLOQ Y. 


external  water  through  a  small  circular  opening  in  the  front 
flattened  wall  of  the  cup.  The  eye  is  a  camera  constructed  on 
the  "  pin-hole  "  type,  the  image  being  defined  by  the  exclusion 
of  all  the  more  divergent  rays  of  light  which  pass  in  from  the 
object  towards  the  eye. 

In  the  remaining  forms  the  eyes  (Fig.  156,  />)  are  large 
globes  imbedded  in  an  orbit  formed  by  the  lateral  portions 
of  the  cephalic  cartilage  and  its  processes.  The  retinal  por- 
tion of  the  eye  closely  resembles  that  of  Nautilus,  consisting 
of  an  external  layer  of  rods  (r)  bounded  beneath  by  a  pigment- 
layer  ipg)  beneath  which  is  a  nerve-layer  (w)  enclosed  within 
a  connective  tissue-sheath  in  which  cartilage  (c)  is  developed. 
The  optic  nerve  dilates  into  a  retinal  ganglion  before  being 
distributed  to  the  retina,  the  rods  of  which,  it  will  be  notetl» 
are  turned  towards  the  source  of  light.  The  eye-cup  differs^ 
however,  from  that  of  Nautilus  in  being  comjdetely  closed, 
and  the  cells  which  form  the  outer  and  inner  layers  of  the 
outer  wall  of  the  cup  secrete  chitinous  material  Avhich  acts 
as  a  lens  (?),  forming  a  powerful  biconvex  condenser.  In  ad- 
dition to  this  the  eye  is  further  complicated  by  the  develop- 
ment of  a  series  of  folds  from  the  skin  in  its  neighborhood. 
One  such  fold  is  developed  from  the  front  Avail  of  the  optic 
sac,  surrounding  the  region  occupied  by  the  lens  and  form- 
ing an  iris  (n-),  the  circular  opening  in  its  centre  correspond- 
ing to  the  pupil  of  the  Vertebrate  eye.  A  second  likewise 
forms  nearer  the  base  of  the  optic  sac  and,  growing  forward, 
may  enclose  a  space  bounded  behind  by  the  iris  and  lens, 
resembling  the  anterior  chamber  of  the  Vertebrate  eye,  the 
portion  of  the  fold  immediately  in  front  of  the  lens  becoming 
transparent  and  forming  a  cornea  {co).  The  iinterior  chamber 
is  not,  however,  closed  in  all  forms,  but  remains  in  communi- 
cation wdth  the  exterior  by  an  aperture  produced  by  a  failure 
of  the  edges  of  the  fold  to  unite  completely.  Finally,  in  sonu^ 
forms  other  folds,  which  from  analogy  have  been  termed  eye- 
lids, develop. 

The  reseaibliince  of  such  an  eye  to  that  found  in  the  Vertebrates  is  ex- 
ceedingly striking,  but  a  detailed  study  of  tlie  structure  and  mode  of  .origiiv 
of  the  various  parts  demonstrates  conchisively  tliat  tlie  similarities  are  ana- 
logical only  and  not  homological.     Uue  of  the  most  important  of  the  ilitfer 


TYPE  MOLLUSCA. 


353 


he  front 
icted  on 
xclusioii 
rom  the 

L-e  large 
portions 
11  al  por- 
>iisi8tiii<f 
)ignieiit- 
(1  Avithiu 
veloped. 
;e  being 
e  noted, 
»  difters^ 
'  closed, 
s  of  the 
icli  acts 
In  ad- 
develop- 
jorhood. 
he  optic 
id  forin- 
res})ond- 

likewise 
forward, 
,nd  lens, 

eye,  the 
lecomiug 
chamber 
ommuui- 
a  failure 
,  in  sonu^ 
;iied  eje- 


rates  is  cx- 
e  of  .onjj;iii 
es  aro  ana- 
the  ilitfei"- 


ences  is  found  in  the  arrangement  of  the  layers  of  the  retina,  tlio  rods  being 
turned  towards  the  light  as  is  usual  in  Invertebrate  eyes,  while  in  the  Verte- 
brates they  are  reversed,  the  nerve-fibre  layer  lying  above  them,  the  light 
of  necessity  penetrating  it  before  reaching  the  rods.  The  structure  of  the 
lens  is  again  very  different,  being  cellular  and  formed  as  an  invagination  of 
the  ectoderm  in  the  Vertebrates,  while  in  the  Cephalopods  it  is  a  cuticular 
structure.  These  are  fundamental  differences  and  may  suffice  to  show 
wiuit  is  meant,  but  many  other  dissimilarities  may  readily  be  found. 

Otocysts  also  occur  imbedded  in  a  capsule  forming  part 
of  the  cephalic  cartilage.  They  have  the  characteristic  Mol- 
luscan  form  and  receive  a  large  nerve  arising  from  the  cere- 
bral  ganglion.  Osphradia  occur  only  in  Nautilus,  where  they 
form  a  pair  of  sensory  papillae  one  of  which  lies  at  the  base 
of  each  of  the  more  ventral  ctenidia.  Other  Cephalopods, 
though  lacking  these  structures,  are  yet  jn-ovided  with  special 
olfactory  organs  in  the  form  of  a  i)air  of  fossae  or  grooves 
lined  by  ciliated  and  sensory  cells  and  situated  above  the  eye 
in  the  position  occupied  by  the  eye-tentacles  of  Nautilus 
(see  p.  358),  from  which  they  may  possibly  have  been  derived. 

The  excretory  organs  consist  of  two  comparatively  large 
sac-like  nephridia  except  in  Nautilus,  in  which,  in  harmony 
with  the  number  of  ctenidia  and  auricles,  there  are  four.  In 
Octopus  and  the  other  members  of  the  group  Octopoda  the 
two  nephridia  are  quite  separate  from  one  another,  but  in  the 
group  Decapoda,  to  which  Loligo  aad  Sepia  belong,  they  are 
placed  in  coinmunicatiou  with  one  another  by  transverse 
canals  one  of  Avhich  may  be  produced  dorsally  into  a  large 
sac  occupying  a  great  portion  of  the  anterior  region  of  the 
body.  The  ventie  cavaj  and  branchial  veins  lie  between  the 
walls  of  this  anterior  sac  and  the  jjaired  posterior  nephridia, 
and  along  the  course  of  the  veins  the  walls  of  the  excretory 
sacs  are  richly  folded  (Fig,  154,  ne),  constituting  the  venous 
a])peudages,  for  a  long  time  considered  to  be  the  excretory 
organs  in  their  entirety.  The  posterior  paired  nephridia 
l)reseut  the  same  relations  to  the  exterior  and  to  the  entero- 
ccel  which  exist  in  other  Mollusca,  opening  by  two  distinct 
apertures  into  the  mantle-cavity  on  the  one  hand,  and  on  the 
other  communicating  with  the  large  enterocoel  which  has 
been  shown  to  be  the  equivalent  of  the  pericardial  cavity  of 
the  Crasteropods  and  Pelecypods. 


3o4 


IN  VERTEBRA  TE  MORPHOLOG  Y. 


The  reproductive  organs  are  situated  near  the  dorsal  ex- 
tremit}^  of  the  visceral  hump.  The  sexes  are  alwaj's  sepa- 
rated iu  different  individuals,  there  being  occasionally  well- 
marked  differences  between  the  two  sexes  of  the  same  species, 
as  in  Argonauta,  the  female  of  Avhich  possesses  a  well-devel- 
oped shell  which  tlie  male  lacks.  The  ovary  (Fig.  157,  ov)  is 
single  and  is  enclosed  in  a  capsule  (c)  formed  hy  the  walls  of 
the  enterocoel  or  viscero-pericardial  cavity,  into  which  the 
organ  seems  to  project,  though  morphologically  it  is  entirely 
outside  it. 

The  germ-producing  region  is  nearly  always  the  anterior 
surface  of  the  organ,  the  stalked  ova  surrounded  by  their 
follicle-cells  projecting  forward  into  the  capsule,  into  the 
cavity  of  which,  i.e.  into  tlie  viscero-perioardial  cavity,  they 
burst  when  mature.     In  some  forms  the  germ-producing  sur- 


^^^"^'^ 


ov 


Fig.  157,— Female  Reimjoductivk  Ohoans  of  Tremoctopus  tnolaceus 

(ufter  IJRocKI. 

c  =  cnpsule.  ov  =  oviiry. 

oil  =  ovi(l\ict.  rs  =  .scniiii.'il  receptacle. 

og  ~  ovhiucal  gland.  wc  =  ((rlomic  cuual. 

face  becomes  more  highly  folded  and  more  or  less  dendritic 
ill  form,  the  area  over  whi'-li  the  ova  are  formed  becoming; 
thus  much  greater.  The  ova  reach  the  exterior  after  tlioy 
have  passed  into  the  cavity  of  the  ca]isu]e  by  means  of  one 
or  two  complicated  ducts  (od)  opening  into  the  mantle-cavity. 
In  N((Htih(,s  two  ducts  are  ])reseut,  that  of  the  left  side,  liowevfr. 
being  non-functional,  and  in  tlm  Octopoda  and  Home  Decapods, 
Huch  HH  ( Jm ifinsJ i'<'>)}n's.  I'oth  dui'ts  u!'o  ')rt>seiit.  In  otlipr  toruis 
but  a  single   duct  persists,  which,  contrary  to  what  occurs  in 


TYPE  MOLLUSCA. 


365 


Nautilus,  is  that  of  the  left  side.  The  oviduct  opens  into  tJie 
inautle-cavity  at  the  extremity  of  a  well-iuavked  papilla,  its 
terminal  portion  being  richly  supplied  Avith  glands,  and  iu 
addition  in  some  forms  two  small  pear-shaped  glands  are 
attached  to  it  in  this  region.  In  connection  with  the  female 
ducts  there  should  be  mentioned  a  pair  of  glands  which  take 
\nitt  in  the  formation  of  the  investments  of  the  ova,  but  Avhich 
open  quite  separate  from  the  oviduct  into  the  mantle-cavity. 
These  are  the  nidamental  ghinds  which  are  present  in  the 
majority  of  forms,  excluding  the  Octopoda,  and  consist  of  a 
pair  of  large  pyriform  structures  lying  on  the  posterior  sur- 
face  of  the  visceral  mass  ;  iu  connection  with  them  in  some 
forms  are  developed  accessory  nidamental  glands  consisting 
of  a  central  and  two  lateral  portions  whose  ducts  open  into 
the  mantle-cavity  in  chjse  proximity  to  those  of  the  nidamen- 
tal glands  proper.  As  stated,  the  gelatinous  mass  within 
which  the  ova  are  imbedded  is  probably  manufactured  by 
these  glands. 

The  testis  iu  its  general  relations  resembles  the  ovary, 
being  single  and  eucloseil  in  a  capsule  whicli  is  a  portion  of  the 
visoero-pericardial  cavity.  The  organ  is  .ittached  to  the  wall 
of  the  capsule  by  a  thin  band  of  tissue  and  is  iu  most  cases 
uluiost  completely  surrounded  by  the  capsule,  into  the  cavity 
oi!  which  the  spermatozoa  are  slied  when  niatuie.  From  the 
wall  of  the  capsule  the  vas  deferens  arises  and  is  usually  a 
single  tube  opening  upon  the  left  side  of  the  body  into  the 
mantle-cavity.  In  NuntiJuH  there  are,  as  iu  the  female,  two 
tlucts,  tho  right,  however,  being  functionless,  l)ut  in  other 
forms  a  paired  arrangement  is  very  rare.  The  proxinjal  por- 
tion of  tlui  duct  is  a  coiled  vas  detVrcns,  which  ()[)ens  into  a 
tliick-walled  glandular  seminal  vesicle  which  on  its  part  by 
means  of  a  narrow  duct  ])asses  into  a  saclike  structure  kjiown 
as  Xeedham's  pouch  which  finally  passes  into  the  muscular 
penis.  In  most  forms  the  duct  connecting  the  seminal  vesicle 
with  Needham's  pouch  receives  tho  secretion  of  a  special  gland 
known  as  the  ])rostate. 

The  majority  of  the  accessory  structines  connected  with 
the  nude  ducts  are  concerned  in  tlu*  formation  o*'  cases  or 
spermatoi)hores  iu  whicli  a  number  of  sjjcrmatozou  are  eu- 


366 


INVERTEBRATE  MORPHOLOGY. 


closed.  Such  cases  are  cyliudrical  structures  with  a  double 
wall,  and  are  provided  at  one  extremity  with  a  somewhat 
complicated  apparatus  for  the  ejection  of  the  spermatozoa. 
The  exact  method  of  their  formation  is  not  understood,  but 
apparently  the  seminal  vesicles  and  the  prostate  plaj'  an  im- 
portant part  in  the  process,  the  Needham's  pouches  being  a 
reservoir  in  which  they  may  be  stored  up  until  required  for 
fertilization. 

Since  the  genital  capsule  is  a  portion  of  the  viscero-pericardial  cavity, 
and  the  reproductive  ducts  are  continuations  of  its  walls,  these  structures 
must  also  be  regarded  as  prolongations  of  the  enterocoel;  and  indeed  second- 
ary communications  may  exist  between  them  and  the  viscero-pericardial 
cavity  proper.  The  genital  <.'apsule  is  not  completely  separated  off  from 
tiie  rest  of  the  enteroca^l,  so  that  it  might  be  possible  for  the  reproductive 
elements  to  pass  from  its  cavity  into  the  viscero-pericardial  cavity  proper, 
and  so  to  the  exterior  through  the  nephridia,  though  this  method  of  exit 
does  not  seem  to  l)e  made  use  of. 

A  I'emarkable  moditication  of  one  of  the  armlike  processes  of  the  foot 
occurs  in  the  males  of  certain  species  in  connection  with  reproduction. 
The  arm — in  Trcmocfopus  and  l^hilonexis  the  third  arm  of  the  right  side 
of  the  body  counting  from  the  anleric)r  mid  line,  in  Aryonuuta  (Fig.  lo8) 


A  B 

Fio.  158.— Male  of  Arqnnnuin  wxtm  IIe(  ■iocotymzed  Arm 

(ttfler  H.  iMi'i.LKH  from  IlA'rmiiEKi. 

A  -  ami  slill  enclosed  williln  ii  membranous  sac. 
B  =  ui  m  freed  from  the  sue. 

the  third  of  the  left  side— is  at  first  enclosed  within  a  Sftc,  by  the 
bursting  of  which  it  l)ecomes  free,  the  walls  of  the  sac  l>eing  reHectoil 
back  so  as  to  form  a  pouch  which  in  some  unexplained  manner  receives  a 


™i 


TYPE  MOLL  use  A. 


357 


sperraatophore.  The  terminal  portion  of  the  arm,  which  is  traversed 
throughout  its  entire  length  by  a  canal,  is  developed  into  a  long  terminal 
filament  through  which  the  spermatozoa  may  pass  During  copulation 
the  arm  is  probably  thrown  off  and  passes  into  the  luantle-cavity  of  the 
female,  the  manner  in  which  the  spermatozoa  reacli  the  ova  being,  however 
not  yet  understood.  When  first  discovered  in  the  mantle-cavity  of  a  female 
tlie  arm  was  regarded  as  a  parasitic  worm,  and  the  name  Hevtocotijlms  was 
applied  to  it-a  term  which  is  still  retained  on  account  of  its  convenience 
In  other  genera  of  Cephalopods  one  arm  is  generally  peculiarly  modified  in 
the  male— in  the  Decapoda  usually  the  fourth  of  tlie  left  side  and  in  the 
Octopoda  usually  the  third  of  the  right  side,  though  frecjuent  exceptions  are 
found.  This  arm  is  termed  the  liectocotylized  arm,  though  it  is  doubtful 
•whether  it  takes  any  part  in  copulation. 

As  will  be  seeu  from  the  above  deseriptiou  the  genus 
Nautilus  differs  iu  many  important  particulars  from  the  re- 
maiuiug  genera  of  Cephalopods,  and  the  class  is  therefore 
divided  into  two  orders.      " 


1.  Order  Tetrabranchia. 

This  order,  of  which  the  genus  Nnuiilus  (Fig.  159^  is  the 
sole  living  representative,  was  in  former  periods  of  the  earth's 
history  the  dominant  group  of  the  Cephalopods— the  Ortho- 
cerites  of  the  Pala'ozoic  and  the  Ammonites  of  the  Mesozoic 
heiug  extinct  members  of  it.     It  is  characterized  bv  its  mem- 
bers possessing  four  cteuidia,  four  auricles  to  the  heart,  and  lour 
iiephridia;  and  in  addition  there  maybe  mentioned,  as  further 
peculiarities,  the   presence  of  paired  reproductive  ducts,  of 
wl.u'h  the  right  one  alone  is  functional,  and  also  of  direct 
♦•omi.iunication  of  the  viscero-pericardial  cavity  with  the  ex- 
terior  by  two  pores,  and  by  the  occurrence  of  a  single  pair  of 
osplmidia.     For  a  more  detailed  account  of  the  peculiarities 
of  NitniUus  the   preceding  general  description  may  be  con- 
sulted.   It  remains  to  discuss  here  the  shell  and  the  structure 
of  the  foot-lobes- structures  which,  with  the  other  characters 
mentioned,  serve  to  distinguish   Nautilus  from  all  its  living 
congeners. 

The  shell  is  voluminous,  coiled,  and  calcareous,  its  cavity 

H'lug  divided  l)y  a  seri(>s  of  transverse  partitions  into  a  nunl- 

her  of  chambers,  in  the  last— that  is  to  say,  the  youngest— of 

which  tlie  aiiihml  lives,  while  the  remaining  ones  are  flih-d  with 


,¥••»•«« 


"•JCI 


n^ 

1 

? 

■ 

1 

i 

!       1 

i 

i 
1 

■ 

'  I 


i* 


368 


INVERTEBUATE  MORFHOLOGY. 


gas.  The  centre  of  each  partitiou  is  perforated,  aud  through 
the  opening  there  extends  to  the  tip  of  the  shell  a  prolongation 
of  the  body  of  the  animal,  termed  the  sipuncle. 

The  foot  of  Nautilus,  or  at  least  that  portion  of  it  which 
fuses  with  the  head,  has  already  been  described  as  forming  a 
number  of  tentiiculiferous  lobes.  These  lobes  are  arranged 
in  the  female  in  two  series — one  ventral,  consisting  of  threa 


Fig.  \n9.— Nautilus  pompilius,—FEii\i.ii,  with  the  Shell  sectioned  Longi- 

TUDINAM-Y  TO  SHOW   ITS  InTEUNAL  StkUCTUUE  (after  Lkunis  from  Hkrtwio). 

1  =  nmiitle.  7  =  nidiimeulal  glaud. 

2  =  dorsal  lobe  of  niantle.  8  =  sliell-uiuscle. 

3  -  tenlades.  9  =  terminal  chamber  of  shell. 

4  =  lu'ad  cap.  10  =  partiiions    between    the    various 

5  z=  oje.  ciiambers. 

6  =  funnel.  U  =  sipuncle. 

lobes  which  immediately  abut  upon  the  mouth,  aud  a  inoro 
dorsal  ringlike  lobe  the  anterior  portion  of  which  is  de- 
veloped into  a  hood  (4)  which  arches  over  and  protects  the  re- 
tracted  tentacles.  Around  the  margins  of  both  the  veutial 
and  dorsal  lobes  are  arranged  the  tentacles,  each  of  which 
is  filiform  and  capable  of  being  withdrawn  into  the  basal  jxu- 
tion,  which  thu:i  serves  as  a  sheath.  In  addition  to  tlic.se 
tentacles  two  other  tentacles  are  f(nind  in  close  ]n-oximity  to 
the  eye,  one  being  on  its  ventral  side  and  the  otiior  on  its 
dorsal.  In  the  male  the  arrangement  is  very  similar,  except 
that  the  median  lobe  of  the  ventral  series  is  transformed  into 
a  lannllated  structure  aud  does  not  bear  tentacles,  wiiih^  a- 
portion  of  each  of  the  lateral  lobes  of  the  inner  series  is  sepii- 


TYPE  MOLLUSC  A. 


359 


through 
aii'-atiuu 


it  vvliicii 
»rmmg  a 
irrauged 
of  three 


;ed  Lonoi- 

1  Hkrtwio). 


lell. 

ie    various 


a  nioro 
h  i.s  iIb- 
ts  the  re- 
B  veutral 
)f  whith 
asal  |)()r- 
to  these 
siniity  to 
u'  on  its 
,r,  ext'('|it 
iiied  iiili* 
,  Avhih>  ii 
9  is  sepii- 


rated  from  the  rest  of  the  lobe—that  of  the  left  side  becoming 
modified  into  a  conical  structure,  lamellated  at  the  extremity 
and  destitute  of  tentacles,  forming  what  is  termed  the  spadix, 
probably  homologous  with  the  hectocotylized  arm  of  the 
male  Octopods  and  Decapods. 

2.  Order  Dibranchia. 

Tlie  members  of  this  order,  which  includes  the  majority 

of  living  Cephalopods,  possess  but  a  single  pair  of  ctenidia, 

uephridia,  and  auricles,  and  lack 

tJie  direct  communication  of  the 

viscero-pericardial  cavity  with  the 

exterior  as  well  as  the  osphradia 

which   occur  in   Nautilus.      The 

portior.  of  the  foot  which  is  fused 

with  the  head  is  diawn  out  "uto 

a  number  of  arms   provided  with 

suckers,  which  seem  to  represent 

the  tentacles  and  their  sheaths 
found  in  Nautilus.  The  suckers 
are  very  numerous  and  may  be 
arranged  in  from  one  to  four  rows 
on  the  ventral  surface  of  the 
arms,  the  margin  of  each  sucker 
being  in  some  forms  strengthened 
by  a  horny  ring,  which  may  be 
toothed.  The  number  of  the 
arms  varies,  being  either  eight 
or  ten  ;  and,  since,  other  struc- 
tural differences  are  associated 
with  this  difference,  the  order 
"uiy  l,e  divided  into  two  suborders  Pro.  m.-F^Ugo  pallida,  D<,nsAr, 

-the  Octopoda  with  eight  arms,  Vikw  (after  Emkbton  from  Vkkuiu,). 
mcluding  tiio  genera  Octopus,  Tremodopm,  and  Argonauta 
(iMg.  08),  and  the  Docapoda  with  ten  arms,  the  genera  Spt- 
ruh,  OmmaMrephes,  Sepia,  and  Loliyo  (Fig.  lOO)  belonging  to 
this  gri)up.  "         /  fob 

In  the  Deeapoda  tho  ten  arina  are  not  of  equal  size,  one 


i4ip 


360 


INVERTEBRATE  MORPHOLOOY. 


on  each  side  of  the  head,  the  fourth,  counting  from  the  ante- 
rior mid-line,  being  k)nger  than  the  rest,  usually  destitute  of 
suckers  except  towards  the  tip,  and  in  most  species  kept 
retracted  within  a  groove  on  each  side  of  the  head  except 
when  required  for  prehension.  They  are  all  good  swimmers, 
and  the  body  is  elongated  and  provided  with  lateral  tins  of 
greater  or  less  extent. 

A  shell  is  present  in  the  Decapod  a,  but  shows  a  great 
reduction  in  size   and  complexity  from    that   of  the  Tetra- 
branchiates  ;  and  in  order  to  understand  its  homologies  in  the 
different  genera  it  will  be  necessary  to  obtain  an  idea  of  its 
form  in  the  fossil  members  of  the  group  which  occur  in  the 
Mesozoic   rocks   forming  the   fam^y   Belemnitida?.      In^  the 
genus  Iklemnites  (Fig.  IGl,  JJ),  for  instance,  the  shell  consisted 
of  a  terminal  conical  solid  portion,  termed  the  rostrum  (?'), 
the  base  of  which  was  liollow  and  contained  a  chambered 
shell,  the  phragmacone  (/j//),  corresponding  to  the  Nautilus 
shell,  the  anterior  portion  of  the  last  chamber  of  this  being 
elongated  into  a  broad  Hat  process  termed  the  proostracou 
(pr).     By  various  nu)diticati(nas  of  this  structure  the  shells  of 
the  different  living  Dec-apods  have  been  developed.    In  Spiruhi 
the  shell  is  coiled  into  a  spiral  and  is  partly  enclosed  by  tlie 
mantle,  the  rostral  and  proiistracal   portions  having  disap- 
peared.    In  all  other  forms  the  shell  has  a  more  or  less  flat- 
tened   for]ii    and   becomes   completely   enclosed   within   the 
mantle,  folds  of  which   .^row  up  around  it.     In  Sepia  (Fig. 
101,  A)  the  proostracou  becomes  almost  obliterated  and  tlic 
rostrum  (/•)  is  exceedingly  small,  the.  phragmacone  (pi)  form- 
ing  the  })rincipal  bulk  of  the  siiell.    This,  however,  has  become 
very  much  modified— that  iiortion  of  it  which  lies  ])osteriortu 
the  sipuncle  {.s)  ceasing  to  develop,  or  rather  becoming  exceed- 
ingly compact  by  the  various  partitions  lying  in  close  con- 
tact with  one  am)tlier  witlumt  any  intervening  air-chambers. 
These  chambers  are,  however,  developed  in  the  portion  ant'  - 
rior  to  the  sipuncle,  but  ar(^  compaiatively  Hat  and  travers.  d 
by  calcareous    spicules,  so  that   the  shell   has  a  somewlml 
spongy  appearance  and  is  exceedingly  light.     In  other  forms, 
however,  the    ].roostracou  is   the    portion    that   i)ersists,  the 


rostrum  ami  i)iinignia 


(•inn 


liotli  (]isa]5]iC;iring  (Fig.  K>1,  C 


TYPE  M0LLU8CA. 


3C1 


lie  ante- 
dtute  of 
es  kept 
I  except 
imuiers, 

I  lius  of 

a  great 
e  Tetra- 
es  ill  the 
3a  of  its 
r  in  the 
In  the 
ionsisted 
;rnm  (;•), 
ambered 
Nmdilus 
lis  being 
lostracou 
shells  of 

II  Spirilla 
d  by  the 
g  disaji- 
less  Hat- 
thill  the 
pia  (Fij^'. 

and  tlic 
pi)  form- 
s  become 
steriorlc 
g  exceed- 
lose  c'oii- 
hainbois. 
tiou  aiiti'- 
travel's*  (I 
.oniewli.'ii 
er  foriu-^, 
sists,  tlif 
01,  0),  -- 


that  fiually  nothing  is  left  but  a  plate  imbedded  in  the  man- 
tie,  formed  entirely  of  chitinous  material  and  destitute  of  any 
calcareous  substance.  This  forms  the  so-called  "  pen "  of 
such  forms  as  Loligo  and  Ommastrephes  {Fifr.  IGl,  D),  a  slight 


FiG.  161,-DrAORAMs  r.v  SiiEM.  ov  A,  Sepia:  R  BelemviUs  (fossil);  C    Os- 
tr„cou;iti.i.  (lassi!);  and  D,  Ommadrn'hes  u.u.v  v^m',) 
ph  =  i.hm-mocone.  ;.  ^  ,,„„,,„„ 

pr  -  l.roOstracon.  ,  ^  ,i,,„„^.|^. 

tj'iekening  of  the  dorsal  end  of  it  in  some  forms  representing 
tlie  remains  of  the  phragniacone. 

In  the  Octopo.la  the  eight  arms  are  practically  equal  in 
i""g  h,  and  the  body  is  more  massive  than  in  the  ])ecaj)ods 
and  less  suited  for  active  swimming.  The  visceral  hum,)  is  a 
more  or  less  globular  mass,  destitute  as  a  rule  of  lateral  lins. 
;"ul  m  all  forms  a  shell  comparable  to  that  of  the  J)ecapods 
■^  wanting.  Tn  the  females  of  Jnmanta,  however,  a  non- 
'•  'a.nlHn-ed  calcareous  shell  is  present,  to  which  the  body  of 
|l'<'  ammal  does  not  closely  adhere,  but  whicl.  is  iield  in  I'osi- 
"uu  by  the  broad  plate-like  anterior  arms  which  embrace  it 


362 


IN  VERTEBRA  TE  MORPHOLOO  Y. 


\  \ 


It  seems  to  be  a  secretion  of  the  ectoderm  of  the  mantle  and 
visceral  hump,  the  anterior  arms  contributing  only  a  thin 
external  layer. 

Development  and  Affinities  of  the  Cephalopods.  —  The  ova  of  those 
Cephalopods  which  have  been  studied  are  richly  provided  with  yolk,  in 
consequence  of  which  the  development  becomes  considerably  modified, 
definite  traces  of  the  Veliger  condition  being  entirely  lost.  It  seems  clear, 
however,  from  the  marked  development  of  the  head,  the  presence  of  a 
radula,  and  the  general  arrangement  of  the  viscera,  that  the  ancestry  of  the 
group  is  to  be  sought  for  among  the  primitive  Gasteropods,  but  in  forms 
more  primitive  than  any  existing  forms.  The  symmetrical  shape  of  the 
body  and  the  character  of  the  viscero-pericardial  cavity  suggests  forms 
intermediate  in  development  between  the  Amphineuraandthe  Diotocardiate 

Prosobranchs. 

So  far  as  the  various  groups  are  concerned  there  can  be  little  doubt  but 
that  the  Tetrabranchs  are  the  more  primitive  forms,  showing  as  they  do 
less  specialization  of  the  foot,  what  must  be  considered  a  more  primitive 
shell,  and  a  more  general  tendency  towards  a  paired  arrangement  of  the 
organs  than  is  found  in  the  Dibranchs.  The  duplication  of  the  ctenidia 
and  nephridia  mu§t,  however,  be  considered  a  secondary  acquisition.  The 
Decapods,  again,  seem  to  be  on  the  whole  more  primitive  than  the  Octo- 
pods,  the  character  of  the  crelom  and  the  presence  of  a  shell  in  the  former 
being  points  to  which  attention  may  be  called  in  this  connection. 

The  Affinities  of  the  i/oZZwsca.— Attention  has  already  been  called  to 
the  similarity  of  the  typical  Gasteropod  and  Pelecypod  larvas  to  the  An- 
nelid Trochophore,  and  the  evident  conclusion  has  been  pointed  out  that 
the  Annelids  and  Mollusca  are  to  be  traced  back  to  a  common  ancestor 
represented  by  the  Trochopliore.  It  is  difficult  otherwise  to  understand 
the  remarkable  similarity  which  exists  between  the  two  larva?— similarities, 
including  not  only  the  general  arrangement  of  the  locomotor  cilia,  but  ex- 
tending as  well  to  internal  organs,  such  as  the  nephridia.  In  two  respects, 
however,  the  Molluscan  Veliger  differs  from  the  Annelid  Trochophore ;  it 
possesses  a  shell  and  a  foot.  These  features  are,  however,  readily  ex- 
plicable as  a  throwing  back  in  the  ontogeny  of  important  structures  origi- 
nally developing  at  a  much  later  period  in  the  life  of  the  animal— a  phe- 
nomenon of  by  no  means  unfrequent  occurrence.  It  must  bo  admitted, 
however,  that  frequent  modifications  of  the  Trochophore  arrangement  arc 
to  be  found,  as  has  been  indicated  in  the  descriptions  of  the  Amphineura, 
and  these  become  especially  interesting  from  the  fact  that  in  the  former  a 
primitive  arrangement  of  the  parts  oi  the  body  must  be  recognized.  If 
the  Trochophore  represents  an  ancestor,  then  it  might  be  expected  that  it 
would  be  found  more  perfectly  represented  in  the  Amphineura  than  in  tiie 
highly  specialized  Gasteropods,  or  even  than  in  the  Pelecypods. 

It  is  important,  then,  that  the  possibility  of  some  of  the  similar  struct- 
ures of  the  Trochoi)hoi'e  and  Veliger  having  been  iiidependently  acquired 


TYPE  MOLLUSC  A. 


363 


Qtle  and 
r  a  thin 

of  those 
[i  yolk,  in 
modified, 
ems  clear, 
ence  of  a 
stry  of  the 
t  in  forms 
ipe  of  the 
3sts  forms 
tocardiate 

doubt  but 
is  they  do 

primitive 
ent  of  the 
le  ctenidia 
tion.     The 

the  Octo- 
the  former 

1  called  to 
to  the  An- 
d  out  that 
n  ancestor 
inderstand 
imilarities, 
ia,  but  ex- 
o  respects, 
ophore ;  it 
eadily  ex- 
ures  origi- 
lal — a  plic- 
admittod, 
icemen  t  are 
nphineura. 
le  former  a 
^nized.  If 
ited  that  it, 
than  in  the 

lilar  struct- 
!y  acquired 


should  be  kept  in  mind,  especially  in  view  of  another  idea  as  to  the  gene- 
alogy of  the  Mollusca  which  has  been  advocated  by  certain  authors  Ac- 
cording to  this  theory  they  have  sprung  from  Turbellarian-like  ancestors  the 
creeping  surface  of  the  worm  having  become  more  muscular,  and  so  having 
given  rise  to  the  foot  of  the  MoUusk,  the  dorsal  region  of  the  body  elevat 
ing  into  the  visceral  hump.  The  nervous  system  of  the  Amphineura,  with 
Its  ladder-  Ike  arrangement,  miglit  readily  be  deduced  from  the  arransre- 
inen  found  in  the  Platyhelminths,  and  thus  many  points  on  which  the  Tro- 
chophore  theory  throws  no  light  become  intelligible. 

This  tlieory  concerns  itself  mainly  with  tlie  adult  forms,  yet  it  is  not 
unpossible  that  a  reconciliation  between  it  and  theTrochophore  theory  mar 
be  possible.     It  has  already  been  pointed  out  that  the  Trochonhore  mav 
possibly  be  the  representative  of  a  Turbellarian  larva,  and  the  same  idea 
may  be  applied  to  the  Veliger.     In  other  words,  it  is  possible  that  the 
Mollusca  may  have  been  derived  from  the  Turbellaria,  and  that  the  ances 
tral  worms  possessed  in  tlieir  life-history  a  larva  whicli,  independently  of 
the  adults,  underwent  a  series  of  modifications  leading  to  the  Veliger     The 
Vehger  would  then  be  the  descendant  of  a  Turbellarian  la'-va  while  the 
adult  xMollusk  would  be  directly  descended  from  the  Turbellarian      This 
view  may  be  contrasted  with  that  which  regards  the  Trochophore  (includ 
nig  the  Vehger  under  this  term  for  convenience)  as  the  ancestor  by  means 
or  the  following  scheme: 


TUEBELLAEIAN    THEOEY. 


Turbellarian  larva==Turbellarian 
(ancestor)  \ 


"Troeliophore 
TEOCHOPHOEE  THEOEY. 
''Turbellarian 


Annelid 


MoUusk 


Turbellarian  larva 
(ancestor) 


Trochophore 


Annelid 


Mollusk 


SUBKINGDOM  METAZOA. 

TTPE  MOLLUSCA. 

I.  Class  AMPHINEURA—Visceral  hump  not  developed;  bilaterally  sym- 
metrical; shell  represented  by  scattered  spicules  or  by  a  series 
of  ealuareous  plates;  anus  tormiual. 


aBIJS** 


I 


364 


INVERTEBRA TE  MORPHOLOO T. 


1.  Order  Solenogastres. — Shell  represented  by  scattered  culcareous 

spicules.     JVeomenia,  Proneomenia,  Choetoderma,  Dondci'sia. 
3.  Order  Polyplacophora. — Shell  formed  by  eight  plates  on  dorsal 
surface  of  body.     Chiton,  Trachydennon,  ChitoneUns. 
II.  Class  Gasteropoda. — Visceral   hump  usually  well   developed     body 
asymmetrical;  shell  univalved  and  usually  spirally  coiled,  some- 
times absent;  anus  not  terminal. 
1.  Order  Prosobranchin. — Clenidia  present,  situated  in  front  of  the 
heart;  auricle  in  front  of  ventricle;  mantle  edL  j  not  fused  with 
body. 
Heart  with  two  auricles;  two  nephridia  (Diotocardia).     Haliotis, 
Turbo,  Trochus,  JYeritina,  Fleurotoinaria,  Fissurella,  Patella, 
Acintea. 
Heart  with  a  single  auricle  and  a  single  nephridium  {Monotocar- 
dia). 

Dentition  tienioglossate. 
With  creeping  habit.     Cijprad,  Paludina,  Natica,  Ampul- 

laria,  Littorina,  Ci/clostoma,  Calyptraa,  Strombus. 
Wi  h  pelagic  habit  {Hetei-ojioda).      Atalanta,  Carinaria, 
]  terotrac/iea. 
Dfc.-'  :ion  ptenoglossate.     lanthina,  Saalaria,  Solarium. 
Dentition  rachigiossate.     Fusus,  Buccinum,  Nassa,  MureXy 

Purmra,  Oliva,  Marginella. 
Dentition  toxiglossate.     Terebra,  Conus,  Pleurotoma. 
3.  Order  Opisthobranchia. — Clenidia  frequently  absent,  when  pres- 
ent behind  the  heart;  auricle  behind  ventricle;  mantle  vdien 
present  not  fused  by  its  edges  to  body-wall;  shell  frequently 
absent. 
Mantle  present  {Tectibranclda) . 
Foot  with  broad  Hat  sole;  with  creeping  habit.     Bulla,  Jamis, 

Ai)lysia,  Pleurobrandius. 
Foot  with  winglike  parapodia,  jielagic  (Pteropoda). 
With  shell  (jf7teco.w«t«to).    Limadna,  Styliola,  Cymbuliopnis, 
Without  shell  (Gymiinsoinata).     Pnenmodi'rma,  Ciione. 
Mantle  not  developed   {Nndibrauchia).    Phurophyllidia,  PhyV 
liiholK  Limapontia,  Doris,  ^oli.s',  Facellina. 
3.  Order  Pnlmonata. — Ctenidia  wanting;  mantle  fused  by  its  edges 
to  body- wall;  terrestrial  or  aquatic. 
Eyes  at  base  of  tentacles  {BosoinmatopJiora).     Limncca,  P/iysa, 

Planorbis. 
Eyes  at  tip  of  tentacles  (Sti/loni  inafophora).    Helix,  Liinax,  Arion, 
Vaginula,  Daudebardia,  Ondiidium. 
in.  Class  ScAPHOPODA. — Visceral  hump  developed;  bilaterally  symmetrical; 
shell  cylindrical,  open  at  both  ends.     Dentaliuin,  Hipliodenta- 
Hum,  Cadulus. 


I 


calcareous 
ndcrsia. 
oil  dorsal 
y. 

ped  body 
iled,  some- 
ant  of  tlie 
fused  with 

Haliotis, 
I,  Patella, 

Monotocar- 


a,  Ampul- 

nbus. 

'^armaria. 


irium. 
ia,  3Iure,v, 

la. 

vlieii  prcs- 
ntle  when 
fi-equeutly 


'la,  Janvs, 

nbuiiojxsis^ 
'lone, 
ilia,  PhyJ^ 

y  its  edges 

xa,  P/ii/sa, 

a,r,  ArioiL 

minctrical: 
iphodeii/ii- 


TYPE  MOLL  use  A. 


365 


IV.  Class  Pelecypod A— Visceral  hump  not  developed;  bilaterally  sym- 
metrical; mantle  forms  two  lateral  folds;  shell  bivalved;  anus 
terminal. 

1.  Order  P/7>to6/-rtMc/i<rt.— Gill  a  true  ctenidium;  pleural  ganglia  not 

nnited  to  cerebral.     Nucula,  Yoldia. 
3.  Order  i^<7<i/-a«c/t«a.— Gill-filaments  elongated  and  bent  upwards 

at  ends;  cerebral  and  pleural  ganglia  fused.     Anoinia,  3Iytilus, 

Modiolaria,  Area. 

3.  Order  PseudolamelUbranchla.—GlW-fiXameni^  turned   up  at  ends 

and  with  interlamellar  junctions;  cerebral  and  pleural  ganglia 
united.     Peoten,  Ostrea. 

4.  Order  EulamelUbranchia.—Q\\\  filaments  united  to  form  a  plate- 

like gill;  cerebral  and  pleural  ganglia  united.     Venus,  Mya, 
Ematella,  Pholas,  Teredo,  Unio,  Anodon,  Ci/clqs. 

5.  Order  SepUbranehia.~(j\\\  reduced  to  a  muscular  perforated  sep- 

tum between  the  mantle  and  si  )rabranchial  chambers.  Cus- 
pidariu. 
V.  Class  Cephalopoda.— Visceral  hump  developed;  bilaterally  symmetri- 
cal; mantle  a  circular  fold;  foot  (propod mm  ami  mesopodmm) 
forming  arm-like  structures  provided  with  suckers  and  sur- 
rounding the  mouth. 
1.  Order   Tetrabranchia.—WiVa  four   ctenidia    and  with    external 

chambered  shell.     Nautilus. 
3.  Order  Dihranchia.—^M\i\\  two    ctenidia  ;    shell   if  external  not 
chambered,  usually  internal. 
With  eight  arms  to  foot  {(Mopoda).     Argonauta,  Octopus,  Treni- 

octopu.s\  P/i  ilonexis. 
With  ten  arms  to  foot   (Decapoda).      Spinda,   Sepia,   ZoUgo, 
Ommastrephes. 

LITERATURE. 

GENEKAL. 

Gould  and  W.  G.  Binney.     The  Invn-tebrata  of  North  Amenca.     Boston,  1870, 

G.  W.  Tryon  and  H.  A.  Pilsbry.  Mdiiual  of  Conrhology.  In  course  of  publi- 
cation.    I'hihulcliiliia. 

S  P.  Woodward.     .1  Ma  mini  of  the  Mollmea.     3d  ed.     London,  1878. 

E.  R.  Lankester.  Avtide  '•  Mollusca."  Encyclopspclia  Britannica,  9th  Ed. 
iiundon,  18S;i 

W.  Patten.  The  Eyes  of  Mollitsks  and  Arthropods.  Mitth.  a.  d.  Zool.  Station 
Neupel,  VI,  188G. 

AMPHIXEURA, 

B.  Haller.     Die  Orgnnisation  de    Chitonen  dcr  Adrin.     Arbeiten  a.  d.  Zoolog. 

liistitut  Wi.-n,  IV.  1883;  v,  188:{. 
H.  N.  Moseley.     On  the  Presence  of  l<:y<s  in  the  Shells  ofrertaiu  rhltonUhp  and, 


-5 


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11.25 


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■^  IM  III  2.2 

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1.8 


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366 


INVERTEBRATE  MORPHOLOGY. 


Quarterly  Journ.  Microscop.  Science, 


Ar- 


on  the  Structure  of  these  Organs. 

XXV.  1885. 
H.  J.  Pruvot.    L'orgaimation  de  quelquea  Neomeniens  dea  Cotes  de  France. 

chives  de  Zool.  exper.,  2me  Ser.,  ix,  1891. 
S.  Wiren.     Studie7i  uber  die  Solemgastres.    I.  Monographie  des  Cheetodei-ma 

nitidulum.     Svensk  Vetenskap,  Akad.  Handl.,  xxiv,  1892. 

GASTEHOPODA. 

Alder  and  Hancock.    A  Monograph  of  the  British  Nudibranchiate  Mollusca. 

London,  1850-51. 
J.  W.  Spengel.     Die  Oertichsorgane  und  das  Nervensystem  der  Moilusken. 

Zeitscbr.  fUr  wissenscb.  Zoologie,  xxxv,  1881. 
H.  L.  Osborn.     On  the  Gill  in  some  Forms  of  Proaobranchiate  Mollusca.    Studies 

from  the  Biolog.  Labor.  Jobns  Hopkins  Univ.,  in,  1884. 
B.  Haller.    Beitriige  eur  Kenntnias  der  Niere  der  Proaobranchier.    Morpholoff 

Jahrbucb,  xi,  1885. 
H.  Simroth.     Versueh  einer  Naturgeschichte  der  deutschen  Nacktschnecken  und 

threr  europaiachen  Vericandten.    Zeitscbr.  fUr  wissenscb.  Zoologie,  xlii, 

1885. 

W.  0.  Binney.     A  Manual  of  American  Land-ahella.    Bulletin  U.  S  National 
Museum,  No.  28,  1885. 

BelaHaller.     Unterauc/mngeniiber  marinenRhipidoglosseii.    Morpbolog  Jabr 
bucb,  IX,  1883  ;  xi,  1886. 

E.  L.  Bouvier.     Syatime  nerveux,  morphologic  genernle,  et  rlaaaification  dea  Gas- 

terojmlea  proaobrancliea.    Annales  Sciences  Nat.,  Zool.,  Ser.  7me,  in,  1887. 
B.  Hallar.    Die  Morphologie  der  Proabranchier  gcmmmelt  aiif  einer  Er'dumae- 

gelung  durrh  die  konigl.  ital.  Corvette  "  Vettor  Piaani."    Morpbolog  Jabr- 

bucb,  XIV,  1888;  xvi,  189() ;  xviii,  1892. 
P.  Polseneer.     Report  on  the  IHeropoda.     Scient.  Results  of  tbe   Voyage  of 

H.  M.  S.  Cballenger.  Zoology,  i.viii.  1887 ;  Lix,  1888  ;  i.xv,  1888. 
J.  I.  Peck.     On  the  Anatomy  and  Iliatology  of  Cyvibuliopsia  calceola.     Studies 

from  tbe  Biol.  Labor.  Jobns  Hopkins  Univ.,  iv,  1889. 
A.  Lang.     Verauch  einer  Erklarung  der  Aaymmetrie  der  Gasteropoda.   Viertel- 

jabresscbr.  Natnrf.  Oesellscb.  Zl\ricb,  xxxvi,  1891. 

E.  von  Erianger.  Ziir  Entwickelung  vonPaliidinavinpara.  Morpboloir  Jabr 
bucb,  XVII,  1891.  **■ 

H.  von  Ihering.  Morphologie  und  Syatematik  dra  Genitalapparatea  von  Helix 
Zeitscbr.  fUr  wissenscb.  Zoologie,  i,iv,  1892. 

SCAIMIOI'ODA. 

H.  de  Lacaie-Dnthieri.  Iliatoire  de  V organ iaaf ion  et  dv  developpement  dii  Dentak 
Annnles  des  Sci.  Nat.,  Zool.,  4mH  Ser.,  vi,  1856  ;  vii,  1857  ;  viii    1858 

L.  H.  Plate.  Ueher  den  Ban  und  die  Veru>,ridfaehaftsbeziehung'en  der  Sole  no- 
conehcn.     Zoolog.  .labrbUcbor,  Anat.  Abtb.,  v,  1892. 

rEI.KCVI'ODA. 

R.  H.  Peck.  The  Strurture  ■)/  the  Lame.llibranch  Gill.  Quarterly  Journ.  Wl- 
croscop.  Science,  xxvi,  1876. 


C. 

w. 

B. 
P. 
J. 

B. 

J.: 

€.  I 
P.] 


TYPE  MOLLUSCA. 


367 


)p.  Science, 
ranee.  Ar- 
Vtcetodeiina 

i  Mollusca, 

Moiluaken. 

1.    Studies 

tforpliolog. 

lecken  und 
ogie,  XLii, 

5.  National 

olog.  Jabr- 

n  des  Gas- 

,  HI,  1887. 

Erd}imse- 

ilog.  Jabr- 

^'^oyage  of 

8. 

.     Studies 

;.   Viertel- 

)log.  Jabr- 

von  Jlelix. 


C.  Orobben.  Ueber  die  Pericardialdrme  der  Lamellibranchiaten.  Ein  Beitrag 
zur  Kenntnias  der  Anatomie  dieser  Mollmkenklasse.  Arbeiten  a.  d.  Zool. 
Institut  Wien,  vii,  1888. 

W.  M.  Bankin.  Ueber  das  Bqjanus'schen  Organ  der  Teichmuschel  (Anodonta 
Cygnea,  Lam.).     Jenaiscbe  Zeitscbr.,  xxiv,  1890. 

B.  Bawitz.     Der  Mantelrand  der  Aceplialen.    Jenaiscbe  Zeitscbr.,  xxii,  1888  ; 

XXIV,  1890  ;  XXVII,  1892. 
P.  Pelseneer.     Oonti'ibutio?i8  a  I'etude  des  Lamellibranchea.    Archives  de  Bio- 

logie,  XI,  1891. 
J.  Tbiele.     Beitrdge  zur  vergleichenden  Anatomie  der  Amj)?iineui'en,  Zeitscbrift 

ftlr  wissenscb.  Zoologie,  lviii.  1894. 

CEPHALOPODA. 

E.  Q^on.  Article  "  Cephalopoda."  Todd's  Cyclopaedia  of  Anatomy  and  Pby- 
siology,  I.     London,  1836. 

J.  Brock.  Zur  Anatomis  und  Systematik  der  Cephalopoden.  Zeitscbr.  fUr  wis- 
senscb.  Zoologie,  xxxvi,  1882. 

C,  Grobben.     Mjrphologische  Studien  iiber  den  Harn-  und  OeacMechtaapparat 

soicie  die  Leibeahohle  der  Cephalopoden.  Arbeiten  e.  d.  Zoolog.  Instiiut  Wien 
V.  1884. 

P.  Pelseneer.  Sur  la  valeur  morphologique  des  bras  et  la  composition  du  systems 
iierveux  central  des  Cephalopodes.    Arcbives  de  Biologie,  viii,  1888. 


uDentale. 
I,  1858. 
er  Soleiio- 


ourn.  Mi- 


868 


INVERTEBRATE  MORPHOLOOT. 


CHAPTEB   XIII. 


TYPE  CRUSTACEA. 


The  group  Crustacea  includes  a  very  large  number  of 
forms,  most  of  which  are  mariue,  though  many  are  found  iu 
fresh  water  and  a  few  are  even  terrestrial.  A  great  diversity 
of  form  is  found  m  the  various  members  of  the  group,  but  at 
the  same  time  the  general  structure,  except  in.  forms  degen- 
erated by  parasitism,  shows  comparatively  close  similarity 
throughout. 

The  body  is  enclosed  in  a  thick  chitinous  cuticle  which 
not  infrequently  becomes  hardened  by  the  deposition  of 
calcareous  matter  in  it,  producing  what  may  almost  be  con- 
sidered a  shell  and  giving  origin  tv)  the  name  aj)plied  to  the 
group.  This  covering  serves  not  only  for  protection,  but  also 
as  a  point  iVappui  for  the  insertion  and  origin  of  muscles. 
Where  it  reaches  a  considerable  thickness  it  becomes  more  or 
less  regularly  divided  into  segments,  separated  by  intervals  in 
which  the  cuticle  remains  thin,  so  that  movement  of  thu 
various  segments  upon  each  other  are  possible. 

As  a  rule  there  is  attached  to  the  sides  of  each  of  these 
segments  an  api)endage,  also  inclosed  iu  a  more  or  less  thick 
cuticle  and  jointed,  this  jointed  character  having  suggestt'd 
the  reference  of  the  Crustacea  together  with  the  Arachnida 
and  Tracheata  to  a  single  group  termed  the  Arthropoda.  An 
examination  of  the  internal  parts,  especially  of  the  nervous 
system,  shows  that  these  various  body-segments  are  in  realitv 
metameres,  and  that  the  Crustacean  is,  like  the  Annelid.  ;i 
motameric  organism.  A  characteristic  of  tlie  Crustacea,  how- 
ever, is  a  tendency  towards  a  greater  <lifferentiation  and  con- 
solidation of  the  metanu^res  than  is  found  in  the  Annelida,  ;i 
tendency  es])ecially  well  marked  iu  the  anterior  region  of  tlio 
body,  wher>»  a  vai'ving  number  of  the  nu^tanieres  fuse  more  or 
less  perfectly  together  to  form  a  distinct  head,  bearing  the 


~3M 


ijttifa 


TYPE  CRUSTACEA. 


369 


aumber  of 
B  fouud  iu 
t  diversity 
>up,  but  at 
nis  (le^eu- 
similurity 

icie  which 
ositioii  of 
ii  be  cou- 
ied  to  the 
11,  but  also 
f  muscles. 
es  more  or 
itervals  in 
ut   of   thu 

1  of  these 
less  thick 
sugtj^ested 
A.rachui(lii 
locla.  All 
e  nervous 
!  iu  realitv 
A.nueli(l.  ;i 
acea,  how- 
aiul  coii- 
uuelidii,  a 
ion  of  till) 
lO  more  or 
iariug  the 


principal  seuse-orgaiis  aud  the  orgaus  of  mastication  (Fig. 
162),  there  beiug  behind  this  head,  more  or  less  perfectly  dis- 
ti'iguishable,  a  thorax  and  an  abdomen.  Judging  from,  the 
number  of  pairs  of  appendages  arising  from  this  head  region 
it  seems  that  the  typical  number  of  metameres  consolidated 
to  form  it  is  live,  but  to  these  there  must  be  added  an  anterior 
segment  which  does  not  bear  appendages  but  upon  which  the 
eyes  are  developed.  To  these  six  somites  there  are  added, 
especially  in  the  more  highly-differentiated  forms,  a  number 
of  additional  metameres  which  properly  beloug  to  the  thorax, 
the  apparent  extent  of  the  head  region  beiug  thus  increased. 


Fig.  162.— :A  Dedapod  ChustaCKan,  Cambarua. 

There  is  indeed  throughout  the  Crustacea  a  tendency  towards 
what  has  been  called  "  cephalizatiou,"  i.e.,  a  condensation  of 
the  anterior  metameres,  and  as  a  rule  tlie  higher  the  form  the 
greater  is  this  condensation  aud  the  greater  the  apparent  ex- 
tent of  the  head  region.  The  number  of  segments  composing 
tlie  thorax  aud  abdomen  is  exceedingly  variable  in  the  lower 
forms,  but  in  the  higher  there  are  constantly  eight  thoracic 
iuid  seven  abdominal  segments,  the  posterior  one,  termed  the 
telson,  being  alone  destitute  of  appendages.  Frequently, 
especially  in  the  higher  forms  (Fig.  162),  the  thoracic  seg- 
ments consolidate  to  a  greater  or  less  extent,  the  segmentation 
(»t'  this  region  of  the  body  being  indicated  iu  some  forms  only 
by  the  apjiendages  and  the  nerve-ganglia,  and  furthermore? 
lateral  folds  of  the  body-wall  may  project  backwards  from  the 
sides  and  dorsum  of  the  head  or  anterior  thoracic  regions, 
enclosing  the  thorax  or  even  the  entire  body  in  a  firm  cara- 
pace or  else  in  a  bivalved  shell,  someiimos  provided  with 
adductor  muscles. 


s***-. 


370 


IN  VERTEBRA  TE  MORPHOLOG  T. 


The  study  of  the  embryology  of  some  of  the  highor  Crustacea  has 
brought  out  the  fact  that  in  these  there  are  indications  of  a  segment  desti- 
tute of  appendages  but  represented  by  a  pair  of  nerve-ganglia,  immedi- 
ately  succeeding  the  eye-bearing  anterior  segment.  In  tliese  cases,  then, 
the  head  really  consists  altogether  of  seven  segments.  AVhether  this  seg- 
ment represents  the  first  appendage-bearing  segment  of  the  lower  forms 


Pig.  163. --Crustacean  Appendages. 
A,  antennule  of  Craytish,  Camharus;  B,  auteuuulu  of  Copepod,  Oitliona  (after 
UIK8BHKCHT);  C,  auteuuii  of  Camharus;  D,  antenna  of  Phyllopod,  Eulimnadia 
(after  Packard);  as,  sensory  hairs. 

or  whether  in  these  also  it  exists  in  a  degenerate  condition  has  not  yet  been 
determined;  for  convenience  at  present  the  six  fully-developed  head- 
segments  may  bo  considered  homologous  throughout  the  group. 

The  appendages  vary  much  iu  form  in  diflfereut  parts  of 
the  body  and  iu  different  forms.     Those  of  the  head  region 


TYPE  CRUSTACEA. 


371 


Listacea  has 
jment  desti- 
lia,  immedi- 
cases,  then, 
ler  this  seg- 
ower  forms 


'thona  (after 
Vulimnadia 


ot  yet  been 
ped  bead- 

parts  of 
d  region 


are  modified  to  serve  as  seuaory  organs  and  organs  of  masti- 
cation. The  first  pair,  termed  the  first  antennce  or  antennules, 
are  usually  sensory  in  function,  though  occasionally  also  loco- 
motor (Ostracoda  and  some  Copepoda),  and  are  frequently 
supplied  with  peculiar  setpe  supposed  to  be  olfactory  in  addi- 
tion to  others  probably  tactile  in  function  (Fig.  163,  B).  They 
consist  in  their  typical  form  of  a  basal  portion  composed  of 
three  or  four  joints,  the  terminal  one  bearing  one  (Fig.  163,  B) 
or  two  (Fig.  163,  J)  many-jointed  flagella.  The  second  pair,  the 
second  antennce  termed  also  simply  antennce  CFig,  163,  C  and  D), 
are  also  principally  sensory  and  consist  typically  of  a  two-joint- 
ed basal  portion,  bearing  two  many-jointed  branches.  One  of 
these,  that  upon  the  outer  side,  frequently  becomes  reduced  to 
a  scalelike  rudiment  (Fig.  163,  C),  the  inner  branch  persisting  as 
the  fiagellum.  The  third  pair,  the  mandibles,  serve  as  mas- 
ticatory organs  and  are  generally  much  modified  in  correspon- 
dence with  this  function.  Typically  (Fig.  164,  A)  they  consist 
of  a  two-jointed  basal  portion  bearing  two  branches.  The 
proximal  joint  of  the  basal  portion,  however,  becomes  much 
indurated  by  the  thickening  of  the  chitinous  cuticle  and  also 
toothed,  forming  the  mandible  proper,  while  the  remaining  joint 
and  the  two  branches  undergo  reduction  even  to  disappear- 
ance, being  krown  when  present  as  the  mandibular  palps 
(Fig.  164,  C,  mp).  Tho  fourth  pair  are  the  first  maxillm  (Fig. 
104,  B  and  D)  and  serve  like  the  mandibles  for  mastication,  un- 
dergoing a  somewhat  similar  modification.  They  do  not,  how- 
ever, become  so  indurated,  though  one  or  both  of  the  basal 
joints  may  be  provided  with  stift'  setee  and  serve  as  a  jaw,  and 
the  two  branches  more  frequently  persist  than  in  the  mandi- 
bles. The  fifth  pair,  the  second  maxilla',  are  also  masticatory 
and  resemble  the  first  in  the  modifications  which  they 
undergo. 

The  thoracic  and  abdominal  appendages  in  all  but  the 
lowest  forms  can  be  reduced  to  a  typical  appendage  consisting 
of  a  two-jointed  basal  portion  tipped  by  two  branches  also 
jointed.  In  appendages  employed  for  swimming  both 
branches  persist  (Fig.  165,  A),  and  may  possess  a  broad 
])latelike  form,  but  when  modified  for  walking  the  outer 
branch    disappears.       From   limbs   modified   in   this   latter 


it 


372 


INVERTEBRATE  MORPHOLOGY. 


Fi0.  164.— Ckdstacean  Appenuages. 
A,  mandible  of  Copepod,  Notodelphys  (from  Bronn);  B,  first  maxilla  of  Noto- 
delphys  (from  Bhonn);  C,  nmndible  of  Cambarus;  D.  first  maxilla  of  Cam- 
barus. 
en  =  eudopodite.  ex  =  exopodite.  mp  =  mandibular  palp. 


ex 


Fig.  165. — Cuustacean  Appendages. 
A,  second  thoracic  appendage  of  Mt/sis  (after  Sahs);  B,  second  tlioracic  appen- 
dage of  an  Amphipod. 


Hi 


TYPE  CRUSrACEA. 


373 


ilia  of  Noto- 
11a  of  Cavi- 

ir  palp. 


mauuer  the  grasping  claws  (Fig.  165,  B)  or  cLeli»  are  devel- 
oped by  tl'.e  liexioii  of  the  terminal  joiut  on  the  subterminal  or 
by  the  elougatiou  of  the  angles  of  the  latter  into  a  more  or 
less  strong  process  against  which  the  terminal  joint  may  be 
approximated. 

The  description  given  above  of  the  various  appendages  is 
of  course  general,  the  modifications  found  in  the  various 
forms  being  almost  endless.  Indeed  in  parasitic  forms  the  ap- 
peudages,  except  those  concerned  in  mastication,  may  entirely 
disappear,  all  gradations  between  fully-developed  append- 
ages and  the  merest  rudiments  being  found  in  various  forms. 


icic  appeu- 


Fig.  166.— Sixth  {A)  and  Second  (B)  TnoijAcxc  Appendages  op  Bkanchio- 

POD,  Apus  (after  Zaddach  from  Bronn). 
hr  =  bract.  fl  =  Uabelluni.  l~6  -  iuuer  lobes. 

From  what  has  been  said,  however,  it  may  be  seen  that  typi- 
oally  the  Crustacean  appendage  may  be  considered  a  biramous 
structure,  consisting  of  a  two-Jointed  basal  portion  termed 
the  protop(,dite  and  two  jointed  branches  termed  the  exopodite 
and  emfopodite  (Fig.  165,  ex,  en)  accordinj,'  to  their  relation  to 
the  median  axis  of  the  body.  Additional  rami  are  frequently 
developed  upon  the  i)r()t()podite— such,  for  example,  as  that 
termed  the  cpipudife  (Fig.  167,  ep)  and  the  branchia  (hr).  How- 
ever, although  such  a  limb  may  be  considered  typical,  it  is 
not  necessarily  also  the  most  primitive.  Indeed  wheii  the 
simplest  forms,  such  as  the  Phyllopoda,  are  examined  it  will 
be  found  that  the  more  posterior  appendages  have  a  very 
clilierent  composition.  Thus  in  the  genus  Apm  the  sixth 
tlioracic  appendage  (Fig.  166,  A)  consists  of  a  central  two- 


a'— - 


M:;: 


374 


INVERTEBRATE  MORPHOLOGY. 


jointed  axis  ending  in  a  rounded  lobe  and  bearing  upon  its 
inner  edge  six  lobes  (1-6),  some  of  which  are  united  to  the 
axis  by  a  joint.  On  the  outer  side  are  two  large  lobes,  the 
distal  ono  being  termed  the  fiabellum  (/),  while  the  proximal 
one  is  the  bract  (br)  and  serves  respiratory  purposes.  The 
entire  appendage  has  thus  a  leaflike  form.  In  one  of  the 
more  anterior  appendages,  however,  an  interesting  modifica- 
tion of  this  will  be  found.  Thus  in  the  second  thoracic  ap- 
pendage (Fig.  166,  B)  the  axis 
will  be  found  to  be  more  dis- 
tinctly divided  into  two  joints, 
each  bearing  two  of  the  internal 
lobes  somewhat  reduced  in 
size,  while  the  terminal  one  in 
addition  carries  two  other  lobes, 
the  fifth  and  sixth,  which  have 
become  somewhat  elongated. 
The  fiabellum  and  bract  remain 
nearly  the  same  as  in  the 
first  post  -  genital  appendage. 
If  now  such  an  appendage  be 
compared  with  the  second  tho- 
racic appendage  of  the  Shrimp 
Palcemonetes  (Fig.  167),  a  direct 
homology  of  the  parts  may  be 
discovered.  The  axis  of  the 
Phyllopod  limb  is  represented 
by  the  protopodite  while  the 
exopodite  (ex)  and  endopodite 
{en)  represent  the  two  terminal 
inner  lobes,  the  others  having  disappeared;  the  fiabel- 
lum is  represented  by  the  epipodite  (ep)  and  the  bract  per- 
haps by  the  branchia  (br),  attached  to  the  epipodite  in  this  par- 
ticular limb,  but  free  on  the  more  posterior  ones. 

It  would  appear  probable  from  these  facts  that  the  bira- 
mous  limb  is  really  a  derivative  from  the  more  complicated 
foliate  appendage  possessed  by  the  Phyllopods ;  the  foliate 
condition,  however,  has  given  place  to  such  a  great  extent  to 


Fig.  167.— The  Second   Maxilli 
FED  OF  Palmmonetes. 
br  =  braucbia. 
en  =  endopodite. 
ep  =  tpipodite. 
ex  =  exopodite. 


TYPE  CRUSTACEA. 


375 


the  biramous  that  it  is  most  conveuieiit  to  regard  tlie  latter  as 
the  typical  coutlitiou  in  the  Crustacea. 

Respiratory  organs  are  not  always  present,  but  wVen  they 
are  they  take  the  form  of  thin-walled  outgrowths  of  the  body, 
wall.     lu  some  forms  in  which  the  surface  of  the  body-wall  is 
increased  by  the  development  of  a  bivalved  shell  or  carapace 
the  hning-surface  of  the  fold  serves  for  respiration,  and  may 
be  thrown  into  a  number  of  folds  so  as  to  increase  the  extent 
of  surface,  as  in  the  Gasteropod  Patella.     In  the  majority  of 
cases,  however,  more  or  less  branched  hollow  processes  are 
seated  upon  the  sides  of  the  body  or  on  a  greater  or  less 
number  of  the  appendages,  their  cavities  communicating  with 
the  lacunar  spaces  of  the  body,  so  that  the  blood  can  circulate 
through  them  and  receive  aeration  through  thea-  thin  walls 
In  the  Isopoda  a  certain  number  of  the  appendages  are  de- 
voted  to  the  respiratory  function,    both    the  exopodite  and 
endopodite  being  lamellar  and  thin-walled,  or  else  the  endo- 
l)odite  alone  may  have  this  function,  the  exopodite  serving  as 
a  covering-plate  for  the  protection  of  the  inner  respiratory 
ramus. 

As  already  stated,  the  body  is  covered  by  a  chitinous  or 
more  or  less  calcareous  cuticle.     This  is  secreted  by  the  cells 
of  the  hypodermis,  as  it  is  termed,  which  correspond  to  the 
ectoderm  of  other  forms  and  rest  below  on  a  more  or  less 
well-developed  layer  of  connective  tissue.     A  dermal  muscu- 
lar system  is  entirely  unrepresented  in  the  Crustacea,  owing 
no  doubt  to  the  development  of  the  thick  cuticula  ;  but  never- 
theless muscles  are  well-developed.     These  take  the  form  in 
the  body  of  four  longitudinal  bands,  two  situated  dorsally  and 
two  ventrally,  giving  off  slips  to  be  inserted  into  the  cuticle 
of  each  metamere,  flexion  and  extension  of  the  various  meta- 
lueres  upon  one  another  being  thus  permitted.     In  addition 
muscles  extend  from  the  body-wall  to  the  various  appendages 
and  between  the  various  joints  of  these  structures,  being  in 
all  cases,  it  is  needless  to  say,  situated  within  the  body  and 
the  appendages.     In  some   cases,    more   especially  in  those 
forms  in  which  the   appendages  are   adapted    for  walking, 
special  chitinous  plates  or  processes  project  into  the  body- 
cavity  from  the  ventral  surface  forming  the  endophragnml  sys- 


^31 


11 


ll# 


376 


INVEHTEDIiA  TK  MOlil'lIOLOG  Y. 


tern  aucl  serving  for  the  attaclimeut  of  the  muscles  passing  to 
the  appendages.  In  forms  furnished  with  a  bivalved  shell 
special  adductor  muscles  for  its  closure  are  frequenth'  devel- 
oped ;  and  in  the  higher  Crustacea,  in  which  the  so-called 
stomach  is  usually  provided  with  a  series  of  chitiuous  teetli, 
special  muscles  are  developed  for  their  movement. 

The  ccelom  of  the  Crustacea  consists  for  the  most  part  of 
a  series  of  cavities,  without  definite  walls,  between  the  viscera 
and  the  muscle-bundles  and  extending  out  into  the  ajjpend- 
ages  and  the  braucliiio.  One  of  these  occupies  the  mid-line 
below  the  dorsal  surface  of  the  body,  and  contains  the  heart, 
whence  it  is  known  as  the  pericardial  sinus.  It  is  bounded 
below  by  a  distinct  partitif)n,  the  pericardial  septum,  but 
seems  to  be  a  schizoccelic  space,  since  it  contains  blood,  and  is 
therefore  not  comparable  to  the  pericardial  cavity  of  the 
Mollusca.  A  true  enterocoel  does  exist,  however,  in  some  of 
the  higher  forms  (e.g.,  Palcemonetes),  consisting  of  a  sac  Ij'ing 
in  the  anterior  thoracic  region.  It  surrounds  the  anterior 
aorta  as  a  narrow  cavity  and  behind  expands  so  as  to  cover 
the  anterior  portion  of  the  reproductive  organs,  and  then 
})asses  ventrally  into  the  schizoccelic  cavity  which  surrounds 
the  intestine.  It  is  a  perfectly  closed  sac,  having  no  com- 
munication with  the  pericardial  sinus  beneath  which  it  lies, 
and  contains  a  coagulable  fluid  in  which  no  corpuscles  have 
been  observed. 

The  sticlike  cavity  into  which  the  anteiuiary  gUmd,  to  be  described 
later,  opevis  is  also  to  be  regarded  as  a  true  enterocoil;  but  attention  miisl 
;i»gain  be  called  to  the  iuadvisability  of  maintaining  a  wide  distinction  be- 
tween schizocoelic  and  enterocoelic  spaces.     (See  p.  231.) 

The  circulatory  system  is  comparatively  simple.  In  many 
forms  a  heart  and  distinct  blood-vessels  are  entirely  wanting, 
the  blood  circulating  through  the  lacunar  ccelom  by  tlio 
niovemeuts  of  the  appendages.  In  the  majority  of  forms, 
hoAvever,  a  pulsatile  heart  (Fig.  168,  /*)  is  present,  lying  near 
the  dorsal  surface  of  the  body  in  the  pericardial  sinus,  ex- 
tending in  some  forms  throughout  the  entire  thoracic  and 
abdominal  regions  of  the  body.  More  usually,  however,  the 
heart  is  limited  to  the  thoracic  region,  or  occasionally  is 
almost  eutirel}'  confined  to  the   abdomen,   its   anterior  ex- 


!■'» 


TYPE  CRUSTACEA. 


877 


tremity  encroaching  but  slightly  upon  the  thorax  (Isopoda) 
It  IS  provitied  with  a  varying  number  of  openings  alon/^  its 
sides,  through  which  the  blood  gains  entrance  to  its  cavity 
from  the  pericardial  sinus— the«e  openings,  termed  ostia 
being  guarded  by  valves  opening  inwards  and  preventing 
regurgitation  of  the  blood  during  systole.  From  either  end 
of  the  heart  arteries  arise  which,  after  a  longer  or  shorter 
course  and  many  or  few  branchings,  open  widely  into  the 
lacunar  spaces.  From  these  the  blood  passes  in  some  forms 
into  a  venous  sinus  situated  on  the  ventral  surface  of  the 


an 


Fig.  168. -Diagram  of  Structure  op  Crust ackan  {Cambariuls 


an  =  anus 

ca  =  carupiice. 

ee  =  cerebral  guugliou. 

h  =  heart. 

i  =  intestine. 

I  =  digestive  gland. 
m  =  mouth. 
mp  =  opening  of  vas  deferens. 


ne  =  nephridium. 

s  =  stomach. 
sa  =  sternal  artey. 

te  =  testis. 

tl  =  telsou. 
vd  =  vas  deferens, 
vn  =  ventral  nerve. 
1-6  =  abdominal  segments. 


body,  and  thence  is  distributed  to  the  branchi*,  passing  from 
them  back  to  the  pericardial  sinus,  and  so  to  the  heart  a.^ain 
The  blood  IS  usually  colorless,  tliough  occasionally  greenish, 
m  which  case  it  contains  a  respiratory  copper-containing  pig! 
nient  termed  hsemocyanin,  or  reddish,  in  which  case  the  pig- 
went  is  haemoglobin.  It  consists  of  a  plasma  in  which  float 
aiiKeboid  nucleated  corpuscles. 

The  digestive  system  consists  of  an  almost  straight  tube 
extending  from  mouth  (Fig.  168,  m)  to  anus  (an)  and  divisible 
luto  three  regions.  The  mouth  is  bounded  in  front  by  an 
overhanging  lip,  and  behind  by  a  lower  lip  which  arises  as 
two  separate  parts,  which  by  some  writers  have  been  regarded 


i 


'^ 


378 


IN  VERTEBRA  TE  MORPHOLOG  Y. 


[4 


as  appendages,  though  the  absence  of  a  corresponding  nerve- 
ganglion  tells  very  stron[,'ly  against  such  an  idea.  The  ante- 
rior portion  of  the  digestive  tract  arises  in  the  embryo  as  an 
ectodermal  invagination,  and  is  fre^iuently  lined  throughout 
by  a  chitinous  cuticle.  In  the  higiier  forms  (Malacostraca) 
the  posterior  portion  of  this  foregut  is  enlarged  to  form  a  so- 
called  stomach  (Fig.  108,  s),  in  which  the  chitinous  lining 
thickens  to  form  a  co)nplicated  arrangement  of  teeth,  Avhicli, 
moved  by  special  muscles  extending  frcu  the  stomach  to  the 
walls  of  the  body,  serve  for  the  comminution  of  the  fooil. 
No  salivary  glainls  occur.  The  midgut  is  frequently  of  very 
small  extent,  and  has  usually  connected  with  it  a  digestive 
gland  (Fig.  108,  I)  consisting  either  of  from  one  to  four  pairs 
of  simple  or  but  slightly  branched  cciecal  tubes,  or  else  of  ;i 
mucJibranched  compact  gland  opening  into  the  intestine  1).\ 
two  or  more  ducts.  The  hindgut  (i),  like  the  foregut,  arises 
as  an  ectodermal  invagination,  and  is  usually  lined  with  chitin 
and  unprovided  with  special  glands. 

The  nervous  system  preseniis  a  typically  metameric  condi- 
tion throughout  the  greater  portion  of  the  body,  n  pair  of 
ganglia  occurring  in  each  segment,  united  by  paired  connec- 
tives with  the  gangUa  of  the  preceding  and  succeeding  metu- 
nieres  (Fig.  108,  vn).     In  the  anterior  portion  of  the  body, 
however,  as  well  as  posteriorly,  a  certain  amount  of  conccn- 
tration  and  fusion  of  the  various  ganglia  occu-s.     An  ideal 
condition  in  wldch  no  fusion  has  taken  place  would  show  a 
pair  of  cerebral  ganglia  (Fig.  101),  cr)  with  which  more  or  less 
complicaied  optic  ganglia  are  connected.     From  the  cevel)r;d 
ganglia  couiu  ctives  pass  backward  and  unite  with  a  pair  of 
'^auglia  {(/),  clearly  indicated  in  the  embryos  of  many  of  tli»; 
higher  forms,  but  not  yet  detinitely  known  in  the  Entoni.^ 
straca,  though  ii   seems  probable  tliat  they  occur  in  tli.^' 
also.     The  inetaiaere  and  api)endageo  wlu(-h  shouhl  proiiei  U 
bt^  associated  with  them  seem  to  have  disappeared  ;  that  is 
to  say,  they  are  the  sole  representatives  of  a  metanie'e  mh  r- 
veniiig  between  the  cerebral  and  antennulary  segujents.    Thrso 
^^an'_^lia  are  united  by  !i  pair  of  connectives  with  a  third  piiir 
Mending  nerves  to  the  antennuU'fl  (if),  and  these  again  with  a 
fourtli^pair  belonging  to  the  antennary  metamere  {y*),  and  so 


liug  uerve- 
Tlie  aute- 
bryo  as  au 
;lirouglioiit 
.laoostraca) 
form  a  so- 
lous  lining' 
etli,  Avliioli, 
iiaeli  to  tlie 
t'  tlie  food, 
itlv  of  very 
a  digestive 
)  four  pairs 
>r  else  of  a 
utestine  bv 
egut,  arises 
witli  cliitin 

Qeric  coiuli- 
-,  a  pair  of 
I'fcd  coiiiicc- 
ediug  luetu- 
F  the  body, 
;  of  c'oiu'cii- 
.  Au  ideal 
mid  show  ;i 
i»)re  or  less 
tho  cevebri'd 
th  a  pair  of 
inaiiv  of  tliti 
he  Eut»^iiiO' 
lur  in  these 
lid  properly 
red  ;  tliat  is 
iiiiufvo  iiitcr- 
ents.  Thesis 
a  third  pair 
igaiu  with  a 
;  {(/),  and  so 


TYPE  CRUSTACEA. 


379 


on,  -i.  paa-  of  ganglia  occurring  in  each  metamere  throughout 
the  body.  Such  a  condition  as  this  is  found  only  in  em- 
bryonic stages,  and  even  there  not  always  perfectly.  The 
ganglia,  representing  the  preanteunulary  metamere  fuse  with 
the  cerebral,  as  do  also  the  antennularv,  and  in  higher  forms 
the  antennary  ganglia,  there  bein^-  thus  formed  a  complex 


a'.._.,p 

FlO.  169.— DfAOUAM  OP  Neuvous 

System  ok  Ckihi acean. 
ee  =  cerehrul  giinglion. 
P''  =  second  " 

g'  =  antemiiiliiry  " 
i/''  -  anteiiimry      " 
vin  =  iimiiilil)uliir    " 
mx\  vix'-'  -  iiiiixilliiry  ganglia. 
(e  —  (Bsopliagiis. 
</<'  -  flrst  tlioiacic  ganglion. 


Pig.  170.— Nkuvous  System  op 
(A)  AN  Isoi'oi),  AneUim,  and 

(IJ)  A  BUACIIYUHAN  DEtAPOO, 
Maja  (after  MilnkKuwaudh). 


cerebrum,  whioli,  in  contrast  to  the  simple  cerebrum  {anhi- 
cnrhnnn)  of  the  Annelida,  may  l)e  kn,)wn  as  a  synccrebrum. 
The  remaining  ganglia  may   remain   ])erfectly   separate,  the 

eoimectives    ioiiii'mr    fli^j    •!>(>!•■-    "jifiivi -n-     -» "       u    • 

t...ii,.l,    ..1 i__      1  »  ri 


much  shortened, 


if: 


fuse.    Thus  in  the  C 


or  a  greater  or  less  nund)er  of  thoni 


may 


rayiisii  the  ganglia  of  the  three  posterior 


: 


"■.  Iw'W ' 


J.^ 


380 


INVERTEBKATE  MOItPJIor.OG Y. 


liead-metameres  unite  with  those  of  the  two  iiiiterior  thoracic 
segmeuts  to  form  a  single  gangliouic  mass  lying  behind  the 
ojsophagus  autl  sending  nerves  to  the  appendages  of  the 
somites  represented  in  the  fusion.  Similarly,  in  the  posterior 
region  of  the  body  of  the  Isopoda  all  the  ganglia  of  the 
abdominal  region  may  fuse  to  a  more  or  less  simple  mass 
(Fig.  170,  A,  ah),  and  an  extreme  condition  of  fusion  is  to  be 
found  in  some  Crabs  (Fig.  170,  B),  in  which  all  the  ganglia 
behind  the  antennary  segment  fuse  to  a  single  mass  {i(d)), 
lying  in  the  thorax — a  condition  standing  in  relation  to  the 
reduction  of  the  abdomen  and  the  extensive  concentration  of 
the  head  and  thoracic  regions  which  are  characteristic  of 
these  forms. 

A  sympathetic  nervous  system  seems  to  be  generally 
present,  consisting  in  its  most  complete  condition  of  an  un- 
})aired  nerve  arising  from  the  syncerebrum  and  passing  buck- 
wards  to  be  distributed  to  the  stomach,  and  of  a  medi.ni 
nerve  (Fig.  170,  A,  m)  extending  from  one  pair  of  post(es(»])li- 
ageal  ganglia  to  the  other,  lying  between  the  two  connectives. 

Sense-organs  reach  a  high  degree  of  develo})ment  in  the 
grou]).  Hairs  occur  in  abundance  on  the  appendages  nnd 
body,  the  majority  no  doubt  having  nu^rely  a  mechanical 
function  ;  but  among  them  will  be  found  some  beneath  wliicli 
lie  one  or  more  ganglion-cells,  giving  rise  to  a  nerve  wliicli 
passes  into  the  hair.  These  hairs  ai'e  supposed  to  be  tactile 
in  function.  On  the  autennules  of  many  forms  and  nioit; 
rarely  upon  the  antenme,  hairs  of  sjiecial  forms  occur,  usually 
in  bunches  or  in  rows.  They  may  be  club-shaped  or  cylin- 
drical,  iind  each  has  a  nerve-libre  extending  into  it  without 
dilating  into  a  ganglion-cell  bmeiith  its  base.  To  these  liairs 
an  olfactt)ry  function  has  been  assigned,  and  it  is  noticoahlf 
that  they  are  usually  more  abundant  u})on  the  antennuli's  >>( 
the  males  than  on  those  of  the  females — an  arrangeiiiiiit 
v/hicl»  suggests  a  probable  service  as  guides  in  finding  llif 
latter. 

Eyea  are  very  generally  ])resent  in  the  Crustacea,  ami 
reach  usually  a  hi^h  degree  of  etliciency.  Two  forms  of  cm' 
are  known  a  metlian  unpaired  t)ne,  frecpiently  spoken  of  ;ih 
the  simi)lo  eye,  anil  the  lateral  or  comjiound  eyes.     The  iia- 


TYPE  CRUSTACEA. 


381 


lYAiveA  eye  is  present  in  the  larval  stages  of  probably  all 
Crustacea,  and  persists  iu  a  more  or  less  perfect  form  in  the 
adults  of  most  Entoniostraca,— a  group  wJiich  contains  the 
more  primiti.-^  forms,— and  has  even  been  detected  in  those 
of  some  of  the  higher  forms  (e.g.  Cmngon).  It  consists  when 
well  developed  of  three  patches  of  pigment,  forming  cups  iu 
each  of  which  lies  a  group  of  clear  cells  from  whi  di  nerve- 
libres  arise  passing  to  the  optic  nerve. 

The  lateral  eyes  are  composed  of  a  number  of  units  each 
of  which  possesses  all  thii  parts  of  a  visual  organ  and  is 
termed  an  ommatidium,  and  consequent- 
ly these  eyes  have  been  regarded  as  an 
aggregation  of  a  number  of  individual 
eyes,  whence  the  term  compound  usually 
applied  to  them.  Each  ommatidium  is 
a  complicated  structure  consisting  of 
several  parts  (Fig.  17i).  The  outermost 
layer  of  each  is  a  transparent  cornea 
which  is  continuous  with  the  general 
cuticle  of  the  body,  and  in  some  forms 
is  only  distinguished  horn  this  by  its 
trjuisparency.  More  frequently,  how- 
ever, this  cuticle  becomes  more  or  less 
porfectl}'  divided  into  a  series  of  corneas 
of  an  hexagonal  or  tetragonal  shape, 
one  correspt)nding  .o  each  ommatidium, 

1.1  i«  e     ,^  It  .     .  CltrsTACKAN 

the  surtace  ot  the  eye  thus  acquiring     j^^j^^ 
a  faceted  appearance.     Below  the  cuti-     c  =  cone-cell, 
ch'    come    (he    hypodernial  cells    (^7/)  ^'//=  corneal  liypodcimis. 
which  secrete    it,    arranged   irregular) v  ^'''''=  <'iy^'"lli"<' <<»iif. 
without  reference  to  the  ommatidia  in  ^J'J^ ''i^'"' •'■';>•"'"• 
the  simpler    non-faceted    eyes,    but   m  Uh  ^  iiiabdom. 
the   faceted  eyes  with  two  hypodernial  cell.--,  lying    beneatli 
each     cornea     and    constituting    the     corneal    hvpodermis. 
IJelow  these  come  the  cone  cells  (T),  two  to  four  in  niunber 
as  a  rule  ;  these  are  elongated  cells  a  portion  of  wliose  pro- 
toplasm becomes  converted  into  a  refractive  translucent  bodv. 


Fig.   171. 


DrAOlJAM     OF 
O.MM  ATI- 


le  CI 


ystall 


ine  cone 


{('(n, 


comoosec 


I  of 


as  maiiv  seijments  a> 


!KK: 


53 


i 


f52 


there  are  cone-colls  taking  part   iu  its  formation,  and 


sur- 


1 


382 


INVEUTKBliATE  MOliPIIOLOG 7. 


rounded  upou  the  outside  by  a  delicate  layer  of  protoplasm 
placing  the  part  of  each  cell  above  the  cone  in  continuity  with 
the  part  lying  below  it.  In  the  higher  forms  there  occur, 
partially  surrounding  the  cone-cells,  two  pigmented  cells 
which  seem  to  be  sensory  in  function  and  are  termed  the 
distal  retiuular  cells  {DR).  They  are,  however,  unrepresented 
in  the  lower  forms,  in  which  the  sensory  portion  or  retinula  is 
represented  by  a  single  circle  of  usually  5  cells  {PR)  lying 
l)roximally  to  the  cone-cells  and  surrounding  a  chitinous  rod 
which  is  manufactured  as  a  secretion  from  their  approximated 
surfaces,  and  is  termed  the  rhabdom  {Uh).  These  cells  are 
also  pigmented  and  are  prolonged  below  into  uerve-libres, 
which,  piercing  the  basement-membrane  u])on  which  the  om- 
matidia  rest,  pass  to  the  optic  ganglia.  In  the  higher  Crus- 
tacea, in  which  a  distal  retinula  is  present,  the  rhabdom  is 
formed  by  a  circle  of  eight  cells  (one  of  which  is  almost 
aborted,  so  that  there  appear  to  be  only  seven).  These  con- 
stitute the  proximal  retinula,  and  appear  to  correspond  to  the 
single  retinula  of  the  simpler  forms.  Finally,  a  number  of 
accessory  cells,  usually  pigmented,  may  surround  each  oni- 
matidium,  separating  it  from  its  neighbors,  but  not  appearing 
to  be  essential  constituents  of  the  e^'e. 

The  view  according  to  wliich  those  lateral  eyes  are  regarded  as  an  ag- 
gregation of  a  nurnbor  of  indepemlent  eyes  has  already  been  referred  to. 
It  seems  qiiestional)le,  Ijowever,  if  tliis  be  tiie  correct  interpretation  of 
tiiem  in  view  of  tiie  occnrrencc  of  so-called  compound  eyes  in  tiie  Mollusca 
(Area)  and  tlie  Polycha'tous  Ainielida.  It  seems  more  probal)le  that,  as 
in  these  forms,  the  Ci'iistacean  eye  is  to  be  regarded  as  a  separation  into  a 
number  of  more  or  less  isolated  parts  of  an  originally  continuous  retina, 
a  corresponding  division  of  tin*  originally  simple  refra(;tive  apparatus 
also  taking  place.  This  view  seems  to  harmonize  «iost  satisfactorily  with 
the  facts  of  development. 

Occasional  de})artures  from  the  usual  arrangement  of  the 
eyes  are  to  be  found — as  for  instance  in  Phronhna,  one  of  tlio 
Amphi})oda,  in  which  two  pairs  of  compound  eyes  occur  on 
the  head.  Mention  may  also  be  made  hero  of  the  peculiav 
eyelike  structures  occurring  in  /'jiplnnisia,  one  of  the  Schizo 
])oda.  They  occur  on  the  basal  joints  of  the  aj)})eudages  of 
certain  of  the  thoracic  metameres,  as  well  as  upon  the  ventral 


TYPE  CRUSTACEA. 


383 


otoplasm 
uity  with 
:e  occur, 
ted  cells 
•raed  the 
)reseuted 
iliuula  is 
'A>)  lying 
uous  rod 
:3ximated 
cells  are 
^'e-fibres, 
I  the  oni- 
ler  Crus- 
ibdom  is 
s  almost 
liese  cou- 
ud  to  the 
amber  of 
3ach  om- 
ppeariug 


[  as  an  ag- 
•eferrod  to. 
retatioii  of 
le  Molliisca 
)1('  that,  ii.s 
tioii  into  11 
loiis  retina, 
appanitiis 
itorily  Willi 

iiit  of  the 
ne  of  the 
occur  on 
I  peculiar 
e  Schizo- 
jdagrs  of 
le  vi'iitral 


surface  of  the  abdomen,  and  appear  to  be  rather  phospho- 
rescent than  optic  organs. 

Otocysts  occur  throughout  the  group  Decapoda,  to  which 
the  Crayfish,  Lobster,  and  Crab  belong,  and  consist  of  sacs 
lined  by  sensory  seta3  and  containing  otoliths.  They  aro 
situated  on  the  basal  joint  of  each  of  the  antennules  and  in 
some  forms  are  completely  closed,  though  usually  their  cavity 
communicates  with  the  exterior,  being  guarded  by  a  number 
of  closely-approximated  bristles.  In  the  Schizopoda  similar 
otocysts  occur  in  the  endopodite  of  the  last  pair  of  abdominal 
api)endages,  and  iu  the  Amphipod  Oxycephalm  two  lie  above 
the  syncerebrum.  These  structures,  which  are  usually  spoken 
of  as  auditory  organs,  seem  to  be  rather  sense-organs  of  equi- 
librium. 

In  the  larva)  of  many  forms  and  in  the  adults  of  some 
Eutomostraca  one  or  two  papilla-like  processes  project  from 
the  anterior  surface  of  the  head  and  are  supposed  to  be  sen- 
sory in  function,  though  what  purpose  they  may  subserve  is 
unkuovv^n.  Strong  nerves  pass  to  these  frontal  sense-organs 
which  appear  to  be  of  considerable  importance. 

The  excretory  system  consists  of  two  pairs  of  nephridia, 
one  or  other  of  which  may  be  absent  in  many  forms.  One  of 
these  develops  in  connection  with  the  antennary  segment  and 
opens  to  the  exterior  on  the  basal  joint  of  the  antenna)  (Fig. 
108,  ne),  whence  it  is  known  as  the  antennary  gland,  some- 
times, however,  receiving  the  name  of  the  green  gland.  It 
reaches  its  highest  devel()])ment  among  the  Malacosiraca, 
occurring  iu  many  Eutomostraca  only  iu  larval  stages,  later 
on  degenerating.  In  its  simplest  condition  it  consists  of  a 
coiled  tube  whose  lunien  a])pears  in  souie  cases  to  be  intra- 
cellular, though  iu  others  it  is  undoubtedly  intercellular,  and 
which  terminates  internally  in  a  saclike  dilatation  whose 
wall  is  richly  supplied  with  blood-lacuna-.  In  the  higher 
xornis  (Fig.  172,  A)  a  great  complexity  is  brought  about  by 
*;  ■  development  of  lateral  branches  from  the  tubular  portion, 
and  the  terminal  sac  {s)  may  enlarge  and  fuse  with  that  of 
the  oj)po8ite  side  to  form  a  cavity  of  considerable  size  lying 
in  the  anterior  portion  of  the  thorax  and  termed  the  nophro- 
l)eritoiieal  Hac. 


384 


INTERTEBliATE  MORPHOLOGY. 


fir 


n 


The  second  uephridium  (Fig.  172,  B)  develops  in  couuec 
tion  with  the  secoud  maxillary  segment,  and  opens  usually 
upon  the  appendage  of  that  segment.  It  is  especially  devel- 
oped in  the  Entoniostraca,  in  which  it  may  lie  in  the  folds  of 
the  body-wall  which  form  the  shell,  and  hence  is  usually 
known  as  the  shell-gland.  It  occurs  also  in  the  larval  stages 
of  many  Malacostraca,  and  may  possibly  persist  in  a  degen- 
erated condition  in  the  adults  of  some  forms.     In  structure  it 


sa4 — 


til 


Fig.  172.—^,  Diagham  of  Nephuidium  (Gueen-gland)  op  Aatacus  (after 

Marchal);  B,  SiiELL-GiiANO  «)P  EuUmnndia. 

a  =  teimiiml  sac.  sa  =  saccule. 

resembles  closely  the  antennary  gland,  but  does  not  present 
tlie  complexity  frequently  found  in  that  gland. 

The  majority  of  the  Crustacea  are  bisexual,  hermaphro- 
ditism occurring  only  in  forms  wliich  have  a  ])arasitic  habit 
and  in  some  which  are  sessile  in  adult  life  (Cirrhipedia).  The 
ovaries  or  testes  (Figs.  173,  A  and  B)  are  paired  orgaus  lying 
alongside  of  the  intestine  or  slightly  dorsal  to  that  orguii^ 
transverse  connecting  bars  in  some  cases  passing  from  tlic 
organ  f)f  one  side  to  that  of  the  oth(>r.  Each  organ  mav  h.' 
regarded  as  a  tube,  sometimes  simple,  sometimes  branchtMJ, 
and  lined  on  its  interior  by  an  epitludium  which  gives  ris(> 
to  the  germ-colls.  Speciivl  germ-producing  regions  are  fr(>- 
quently  developed,  as,  for  instance,  at  the  extremities  of  the 
tubes  or  ahmg  one  side  (Isopoda),  the  cells  in  otlior  regions 
ceasing  to  give  rise  to  ova  or  S})ormat()zoa.  The  reproductiv(> 
elements  pass  to  tlie  exterior  hy  s])ecial  ducts,  oviducts  {od) 


[n  couuec- 
is  usually 
illy  devel- 
e  folds  of 
s  usually 
i^al  stages 
1  a  clegeii- 
ructure  it 


TYPE  CRUSTACEA. 


385 


itacus  (after 


t  preseut 

rniapliro- 
itic  habit 
ia).  The 
aus  lying 
at  oi'gaii, 
from  the 
1  luay  1)1' 
)  ranch  I'd, 
;ives  rise 
are  fre- 
es of  the 
•r  regions 
rod  active 
lucts  {(kI) 


or  vasa  deferentia  {vd),  connected  with  each  organ,  and  open- 
ing usually  upon  the  ventral  surface  cf  the  body  at  or  near 
the  junction  of  the  thoracic  and  abdomiural  regions.  The 
origin  of  these  ducts  has  not  yet  been  discovered,  but  it  has 
been  suggested  that  they  may  represent  a  third  pair  of  ne- 
phridia.  Accessory  structures,  such  as  receptacula  semiuis 
and  cement-glands,  for  the  attachment  of  the  ova  in  the  fe- 
males, and  spermatophore-sacs,  in  which  the  spermatozoa  are 
encapsuled  in  spermatophores  in  the  males,  are  frequently  de- 


ov 


Fm.  173.— 4,  OvAHY,  AND  B,  Testis  ok  Mysis  (after  sars). 
oil  —  oviduct.  tb  =  transverse  bar  of  ovary. 

ov  =  ovary.  te  =  testis. 

vd  =  vas  deferens. 

veloped  in  connection  Avith  the  ducts,  and  in  the  Malacostraca 
certain  of  the  appendages  in  the  neighborhood  of  the  genital 
openings  are,  especially  in  the  males,  moditied  so  as  to  serve 
as  copulatory  organs. 

Owing  to  the  great  variety  of  form  and  structure  met 
Avith  in  the  various  species  of  Crustacea  the  grouj)  is  sfc])ara- 
ble  into  a  large  number  of  subdivisions.  Two  principal  classes 
are,  however,  readily  discernible,  of  which  the  tirst  is 

I.  Class  Eiitoiiiostraea. 

In  this  class  the  number  of  segments  (»f  which  the  body  is 
composed  varies  greatly  in  the  various  groups  and  even  in 
closely-related  genera.  The  abdominal  region  is  in  some 
forms  very  mucli  abreviatetl  and  is  destitute  of  appendages,  a 
nile  which,  however,  finds  exception  in  certain  Plvllopods  iu 


s 


.■"::3i3 


386 


INVERTEBRATE  MORPHOLOGY. 


ma 


¥• 


^i 


which  some  of  the  segments  behind  the  genital  openings, 
which  may  be  taken  as  indicating  the  line  of  separation  be- 
tween the  two  regions,  are  provided  with  appendages.  Folds 
arising  from  the  head  region  and  forming  either  a  carapace 
or  a  bivalved  shell  are  frequently  present  and  the  animals  are 
for  the  most  part  small,  the  largest  reaching  a  length  of  about 
€ight  centimetres,  while  the  majority  measure  less  than  a  milli- 
metre. The  unpaired  eye  usually  persists  in  the  adult,  as 
does  also  the  shell-gland,  the  antennary  gland,  on  the  other 
handj  being  usually  rudimentary  or  absent.  A  masticatory 
stomach  is  never  present,  and  a  further  characteristic  is  found 
in  the  fact  that  the  larva  which  hatches  from  the  egg  is  almost 
invariably  a  Nauplius  (see  p.  417). 

1.  Order  Phyllopoda. 

The  Phyllopoda  are  principally  confined  to  fresh  water, 
the  genus  Artemia,  however,  being  found  in  salt  lakes,  while 
a  few  Cladocera  are  marine.     They  seem  to   be    the   most 
primitive  of  all  the  Crustacea  and  present  the  greatest  variation 
in  the  number  of  metameres  composing  the  body,  some  spe- 
cies possessing  over  forty  pairs  of  appendages,  while  in  others 
again  the  number  is  reduced  to  nine.     All  the  thoracic  ap- 
pendages, however,  as  a  rule  bear  branchial  lobes,  and  in  some 
oases  (Apus)  present  the  mauy-lobed  and  imperfectly-jointed 
condition  which  has  been  considered  the  most  primitive  form  of 
the  Crustacean  limb  (see  p.  373).     The  antennules  are  usually 
small  and  abundantly  provided  with   olfactory  hairs,  while 
the  antenna  (except  in  Apus,  in  which  they  entirely  disappear) 
are  long  and  serve  as  locomotor  organs.     The  mandibles  are 
reduced  to  simple  masticatory  plates  without  palps,  and  the 
maxilliB  undergo  likewise  considerable  reduction.     A  heart  is 
always  present,  but  no  blood-vessels  exist,  the  blood  passing 
from  the  heart  into  lacunar  spaces. 

1.  Suborder  Bra?ichiopoda. 

The  Branchiopoda  have  all  a  plainly-segmented  body  con- 
sisting of  many  segments,  and,  with  the  exception  of  Branehi. 
pus  and  Artemia,  are  provided  with  a  fold  of  the  body-wall 


TYPE  CJiUSTACEA. 


387 


•penings, 
Ltion  be- 
.  Folds 
carapace 
mals  are 
of  about 
u  a  inilli- 
adult,  as 
be  otber 
sticatory 
is  found 
is  almost 


li  water, 
is,  wbile 
le  most 
ariatiou 
me  spe- 
i  otbers 
acic  ap- 
iu  some 
-joiuted 
form  of 
usually 
s,  wbile 
appear) 
bles  are 
and  tbe 
heart  is 
passiug 


dy  con- 
iy-wall 


wbicli  may  form  a  dorsal  carapace,  as  iu  Apus,  or  a  bivalved 
sbell,  as  in  Limnadia,  Limnetis,  and  Estheria  (Fig.  174),  an 
adductor  muscle  being  developed  for  tbe  closure  of  tbe  sbell 
witbiu  wliicb  tbe  entire  body  may  be  witbdrawn.  Tbe  anten- 
nules  are  as  a  rule  small  and  are  provided  witb  olfactory 
bairs;  tbe  antenna?,  on  tbe  otber  band,  are  well  developed  ex- 
cept in  Apus,  in  wliicb  tbey  are  in  some  species  quite  small 
and  in  otbers  entirely  wanting.  In  tbe  sbelled  forms  tbey  are 
biramous,  consisting  of  a  several-jointed  protopodite  termi- 
nated bj'  two  many-jointed  fiagella,  and  serve  as  oarlike  loco- 
motor  organs,  but  in  Branchipus  tbey  are  sbort  strong  struc- 


FiG.  174. — Estheria  com'ph.rimanus  (after  Packard). 
a<'  =  auteuiiule.  at-  —  iUilLiiiiii.  m  =  slioll-jniiscle. 

tures  witbout  any  locomotor  function,  serving  in  tbe  males 
as  cbasping  organs  of  use  in  copulation.  Tbe  mandibles  are 
reduced  to  tootbed  plates,  lacking  a  palp,  and  tbe  first  max- 
illiP  sliow  an  almost  similar  reduction,  wbile  tbe  second  are 
entirely  wanting  in  some  genera,  sucli  as  Limnetis.  The  suc- 
ceeding appendages  are  not  limited  to  the  thoracic  region  of 
the  body,  taking  tbe  genital  opening  as  tbe  limit  between  the 
two  regions.  Tbus  in  xipus  cancri/orniis  there  are  eleven 
thoracic  append.ages,  while  bebind  tbe  genital  ring  tliere  are 
no  less  tban  over  bfty  locomotor  limbs,  and  in  sucb  forms  as 
Limnetis  and  Estheria  (Fig.  IT-l)  it  is  difficult  to  distinguisb 
between  tbe  tborax  and  the  anterior  abdominal  segments. 

Tbe  beart  of  the  Branchiopoda  is  a  more  ox  less  elongated 
organ  witb  several  ostia  and  is  usuully  limited  to  the  anterior 
portion  of  tbe  thoracic  cavity,  thougb  in  Branchipus  it  extends 


8S: 


2'l 

12 


:« 


5  * 


388 


INVERTEBRATE  MORPHOLOGY. 


into  the  anterior  abdominal  region.  Lateral  eyes  are  present 
in  addition  to  the  unpaired  median  eye.  In  Branchipm  they 
are  situated  upon  the  sides  of  the  head  upon  well-detined 
stalks,  but  in  Apiis  they  are  closely  approximated  on  the 
dorsal  surface  of  the  cephalo-thoracic  carapace,  while  in  the 
shelled  forms  they  are  united  together  to  form  a  single  eye 
whose  double  nature  is  revealed  only  by  a  study  of  the  details 
in  its  arrangement. 

A  peculiar  feature  in  the  life-history  of  the  members  of  this  group  is  the 
€ompai'utive  iufrequency  of  males,  their  proportion  to  females  being  so 
small  that  for  some  time  they  were  not  known  to  exist.  The  females  are 
able  to  reproduce  parthenogenetically— males  appearing  only  under  certain 
conditions  which  are  not  as  yet  satisfactorily  understood.  The  eggs  de- 
velop generally  in  brood-pouches  situated  upon  certain  of  the  thoracic  ap- 
pendages {Apus,  Limnadia)  or  else  are  affixed  to  fiiamentar  processes  of 
these  appendages  (Estheria). 

2.  Suborder  Cladocera. 

The  Cladocera  are  distinguished  from  the  Brauchiopoda  by 
the  segmei;tati(jn  of  the  body  being  much  less  clearly  defined 
and  by  the  small  and  more  definite  number  of  appenda'-^es, 
there  being  only  from  four  to  six  pairs  of  thoracic  limbs.  A 
bivalved  shell  arising  from  the  maxillary  segments  and  pro- 
vided with  an  adductor  muscle  is  always  present ;  it  does  not 
enclose  the  head,  but  the  rest  of  the  body  may  be  completely 
withdrawn  within  it  except  in  some  genera,  such  as  Ji'vadne 
and  Polyphemus,  in  which  it  is  transformed  into  a  brood- 
chamber,  leaving  the  body  almost  unprotected. 

The  antennules  are  always  small  unjointed  structures  pro- 
vided with  a  bunch  of  olfactory  hairs  usually  terminal  in  po- 
sition, and  the  antenuje  are  strong  biramous  locomotor  organs. 
The  mandibles  are  simple  toothed  plates  without  palps,  and 
the  second  maxillae  are  usually  entirely  wanting  in  the  adults. 
The  tlioracic  limbs  are  six  in  number  in  the  genus  Sida  and 
are  all  lamellate  and  abundantly  supplied  with  marginal  setas 
but  in  Daphiia  (Fig.  175),  Moina,  and  allied  forms  the  number 
is  reduced  to  five,  and  the  more  anterior  ones  are  more  or  less 
modified  tovr'ards  simple  cylindrical  jointed  appendages,  a 
condition  found  in  all  the  four  thoracic  appendages  of  Evadne 


TYPE  CRUSTACEA. 


389 


J  present 
pv^  they 
l-deliiied 
on  the 
le  iu  the 
Dgle  eye 
e  details 


roup  is  the 
s  being  so 
imales  are 
ler  certain 
le  eggs  de- 
loracic  ap- 
ocesses  of 


ipoda  by 
'  defiued 
3iidu<fes, 
iiibs.  A 
md  pro- 
iloes  liot 
upletely 
\  Kvadne 
L  brood- 


ires  pro- 
lil  iu  po- 
■  orgiuis. 
Ips,  uiid 
}  adults. 
Ida  and 
ml  setir, 
number 
e  or  less 
lages,  a 
Evadne 


Pig.  175. — DapJmm  pulex  (from  Hertwig). 


b  =  brood-poucb 
e  =  immature  ova. 
g  =  cerebral  ganglion. 
go  =  optic  ganglion. 
h  =  heart. 
^  =^ermii)al  region  of  ovary, 


0  —  ovary. 

s  =  shell  gland. 

1  =  anteniiule. 

2  =  antenna. 

3  =  mandilile. 

5-9  =  thoracic  limbs. 


-^•K 


^"-'mm 


390 


INVEUTEBHATE  MOUFIIOLOG Y. 


m 


ii 


and  Polyphemus,  the  branchial  lobes  being  at  the  same  time 
rudimentary  or  entirely  wanting.  The  abdomen,  which  is 
composed  of  four  segments,  possesses  on  its  dorsal  surface 
elevations  for  the  closure  behind  of  the  brood-chamber,  and 
on  its  terminal  segment  set*  are  usually  developed ;  it  does 
not,  however,  bear  any  appendages. 

The  heart  is  an  oval  structure  situated  in  the  thoracic  re- 
gion and  possesses  but  a  single  pair  of  ostia.  The  lateral 
eyes  are  in  all  cases  fused  to  form  a  double  eye  situated  in 
the  median  line  of  the  head  and  capable  of  movement  within 
a  socket  by  means  of  muscles  which  are  attached  to  it. 

The  majority  of  the  Cladocera  jiro  fresh- water  forms, 
though  some,  such  as  Evcuine,  are  marine.  The  ova  undergo 
development  in  a  brood-chamber  formed  by  the  space  in- 
cluded between  the  shell-valves  and  the  dorsal  surface  of  the 
abdomen,  and  in  Evadne  and  Polyphemus,  as  already  stated,  the 
entire  shell,  which  is  somewhat  reduced  in  size,  is  adapted  to 
serve  as  walls  for  the  chamber. 

As  in  the  Branchiopoda,  collections  of  Cladocera,  es- 
pecially if  made  during  the  spring  or  summer,  will  show  an 
enormous  preponderance  of  females,  and  several  generations 
may  be  reared  without  a  single  male  making  its  appearance. 
The  eggs,  which  have  a  thin  egg-membrane  and  little  yolk, 
develop  parthenogenetically  and  produce  females,  and  this 
method  of  reproduction  will  continue  so  long  as  the  condi- 
tions, such  as  temi)erature  and  food,  remain  satisfactory; 
hence  the  eggs  of  this  kind  are  generally  known  as  "  summer 
eggs."  Towards  autumn,  however,  or  whenever  the  condi- 
tions tend  to  become  unfavorable,  males,  distinguishable  by 
their  smaller  size,  the  absence  of  a  brood-pouch,  and  their 
more  highly-developtu!  sn^ns-  organs,  as  well  as  by  the  de- 
velopment of  hooked  setie  on  the  anterior  appendages  wliicli 
serve  as  clasping  organs,  make  their  appearance,  and  at  the 
same  time  the  females  begin  to  deposit  ova  much  larger  in 
size  than  the  summer  eggs  and  containing  a  considerable 
amount  of  yolk.  These  "  winter  eggs  "  develop  apparent!} 
only  after  fertilization.  In  Polyphetniis  they  possess  a  thick 
shell,  but  in  other  forms  special  arrangements  .occur  to  render 
them  resistent  to  cold,  drying,  etc.     In  some  fornTs  the  ni.i- 


TYPE  CRUSTACEA. 


391 


jarae  tinu) 
,  which  is 
al  surface 
mber,  aud 
lI  ;  it  does 

loracic  re- 
'he  lateral 
lituated  in 
311 1  within 
>it. 

er  forms, 
a  undergo 
space  in- 
ace  of  the 
itated,  the 
dapted  to 

>cera,  es- 
show  an 
nerations 
pearance. 
ttle  yolk, 
aud  this 
lie  coudi- 
sfactory ; 
*  summer 
le  coudi- 
hable  by 
ind  their 
r  the  de- 
;es  wliicli 
id  at  tln^ 
larger  in 
siderable 
)parently 
}  a  thick 
to  render 
the  ma- 


ternal shell  is  sloughed  and  serves  as  a  protecting  case  ^ut 
more  usually,  as  in  Daphnia,  Moimt,  aud  others,  a  sac"'  c- 
shaped  thickening,  the  eplnpnimn,  appears  on  the  dorsal  wall 
.if  the  brood-pouch  at  the  time  of  the  passage  of  the  winter 
egg  into  it,  and  this  thickening  is  thrown  off  with  the  egg  and 
forms  a  protective  covering  for  it. 

3.  Order   Ostracoda. 

The  Ostracoda  resemble  the  Cladocera  in  the  segmentation 
of  the  body  being  but  slightly  marked  aud  in  possessii..^  a 
bivalved  shell  provided  with  an  adductor  muscle.  The  shell 
however,  encloses  the  head  as  well  as  the  thoracic  and  ub-' 
domiual  regions,  and  furthermore  but  two  thoracic  limba 
exist. 

The  auteuuules  and  autennro  are  both  uniramous  append- 
ages and  serve  for  creeping,  though  the  former  are  also  pro- 
vided with  olfactory  hairs.    The  maudible  consists  of  a  tooth- 
bearing  plate  and  a  strong  jointed  palp  which  in  some  forms 
also  functions  as  a  creeping  limb,  and  behind  it  are  two  well- 
developed  maxilhB.     The  first  of  these  is  distinguished  bv  the 
development  of  the  jaw  portion  and  the  reduction  of  the  palii 
and  in  Cypris  and  Cijthere  bears  a  large  plate  with  nume'  ,)us' 
marginal  setre  which  is  usually  termed  a  branchial  lobe.    The 
second  maxilla,  on  the  other  hand,  shows  considerable  modi- 
ficatiou  in  different  genera.     In  Cypridma  (Fig.  176,  .l/c')  it  is- 
jawlike  and  bears  a  large  branchial  lobe  (wanting  on  the  first 
pair),  and  in  Cypris  is  adapted  for  the  same  function,  but  bears 
m  addition  to  the  rudimentary  branchial  lobe  a  short  two- 
jointed  palp,  which  in  Haloc,/pris  becomes  enlarged  to  form  a 
three- or  four-jointed  limb,  while  finally  in  Cythere  the  append- 
age is  practically  a  walking  limb,  its  jaw  function  not  being, 
developed.      The  tirst  thoracic  appendage  is  an   elongated 
mauy-jointed  limb  except  in  Cypridina  (Fig.  170,  t'),  where  it 
possesses  a  jaw  function,  and  tlie  second  is  also  limblike.     In 
I/alocypris  this  latter  appendage  is,  however,  rudimentary,  aud 
in  Cypris  and  (),pridma  (Fig.  17(),  T')  it  is  dorsally  directed 
and  serves  for  cleansing  the  inner  surface  of  the  shell  from 
J-ieigu  bodies,  in  the  latter  genus  arising  some  distance  ui> 


Sit 


SIfS;: 


■^ 


'i 


892 


INVEIiTEBltA TE  MOliPIIOLOO  Y. 


upou  the  sides  of  the  body  aud  forming  a  long  cylindrical 
uiijointed  appendage. 

Eespiration  is  usually  effected  by  the  general  surface  of 
the  body  and  the  inner  walls  of  the  shell  duplicature,  thou<,di 
in  certain  Cypridinidre  a  double  row  of  respiratory  processes 
are  situated  upon  the  dorsal  surface  of  the  body  near  the 
second  thoracic  appendage.  The  so-called  branchial  lobes  on 
the  inaxilhe  probably  sr.bserve  the  respiratory  function  only 
by  renewing  the  water  in  contact  with  the  body  surface.     A 

oOc      H 


Fig.  nQ.—Ci/priiUna  mediterranea,  Female  (after  Claub). 


At^  =  auteiiiiule. 
A(^  =  iiiiteuuu. 
h  =  heart 
Mnp  =  niiiutlibiilar  pulp. 
Mx\  Mx'  =  tiist  (lud  suc'outl  maxilla. 


0  =  simple  eye, 
Oc  —  roinpomid  eye. 
Pr  —  fioiitiil  orgai). 
8m  =  sliLll-rnu.scle. 
0,  T*  =  first  and  second  thoracic 
appendages. 


single  mediun  eye  alone  is  ])resent  in  Cypru  and  Cytherc,  l)iit 
in  addition  a  pair  of  lateral  compound  eyes  occurs  in  ('i/pr!- 
dina.  The  frontal  sense-organ  is  a  single  strong  process,  in 
certain  forms  lying  slightly  al)()ve  and  betwec  the  antennults. 
A  heart  is  ])res(Mit  in  Cifpridimi  and  Ihilorypris  as  a  sacliko 
organ  with  two  lat«^ral  ostia  and  is  not  j)r()longed  into  arterios. 
In  (hjprifi  and  i'ythere  it  is  entirely  wanting. 

The  Ostracoda  occur  both  in  fresh  water  and  in  the  ocefiii. 
The  genus  CypriH  and  itn  allies  are  for  the  most  part  atjuati*-, 
wliih^  the  other  genera  mentioned  are  exclusively  marine. 


cylindrical 

surface  of 
ire,  tliouf,di 
y  processes 
ly  near  the 
al  lobes  on 
iction  only 
lurface.     A 


TYPE  CRUSTACEA. 


393 


lU8). 


^e. 


!oik1  tliomclc 

'ijtherc,  ])iit 
1  iu  Cypri- 
jrocess,  ill 
mteunult's. 
H  a  sacliko 
to  arteries. 

the  ocBiiii. 
rt  aqiiatio, 
lariue. 


3.  Order  Copepoda. 

The  members  of  the  order  Copepoda  present  great  varia- 
tions  in  form,  due  to  the  fact  that  there  are  a  number  of  para- 
sitic  forms  belonging  to  it  some  of  which  show  so  much  de- 
generation that  their  relationships  to  the  non-parasitic  forms 
only  become  apparent  by  a  study  of  their  development. 
Typically,  however,  the  body  is  generally  elongated  (Fig.  177) 
and  consists  of  ten  segments  in  addition  to  those  of  the  head, 
the  five  anterior  ones  usually  bearing  appendages  and  con- 
stituting the  thorax,  while  the  live  posterior  lack  appendages 
and  form  the  abdomen,  the  terminal  segment  of  which  bears 
a  pair  of  cau  lal  inrcm  provided  with  setfe.  la  female  indi- 
viduals the  tv  T  anterior  abdominal  segments  fuse  together  to 
form  a  genital  doable  segment,  and  in  all  cases  the  head  seg- 
ments fuse  together,  while  the  anterior  thoracic  segment 
usually  fuses  with  this  consolidated  mass.  Xo  shell-duplica- 
ture  occurs.  In  the  parasitic  iovmn  there  h  a  tendency  for 
the  various  segments  to  beco)>\e  indistinct  and  all  trace  t)f 
them  may  vanish,  the  abdomen  in  some  cases  becoming  also 
extremely  reduced  in  size.  Add  to  this  that  lobes  and  pro- 
cesses are  frequently  developed  upon  the  body  and  it  vill  be 
understood  lunv  far  these  degenerate  forms  depart  from  the 
typical  arrangement. 

The  antennules  (Fig.  177,  af)  in  all  free-swimming  Cope- 
poda  form  long  nniny-jointed  swimming-organs  used  in  an 
oarlike  manner.  They  consist  of  a  certain  nund)er  of  stout 
basal  joints,  terminated  by  a  single  hmg  multiarticulate 
Hagellum,  no  trace  of  a  biramous  condition  being  apjiarent.  In 
addition  to  their  locomotor  function  they  also,  as  in  otlier 
forms,  serve  as  sense-organs,  olfactory  hairs  being  scattered 
along  the  flagellum,  and  in  male  individuals  they  are  si)eciallv 
iiioditied  to  form  c]as,)ing  organs  for  use  in  copulation.  The 
uiiteunie  {nf)  are  much  smaller  and  are  frecimmtly  biramotis, 
and  the  mandible  {mn)  has  usually  a  palp,  wiiile  the  first 
niaxilh©  (wx'),  bearing  strong  masticatory  bristles  on  their 
biiSiU  joints,  also  show  more  or  loss  iiidicatiou  of  a  biraiuous 
condition.  The  second  raaxillie  (mx*),  so^uetimes  termed  the 
mi',xillipeds,  have  generally  been  regarded  as  representing  a 


■lk« 


Slls 


394 


INVERTEBRA  TE   MORPIIOLOO  T. 


mx' 


-  mx' 


single  imir  of  appendages  whose  exopodites  and  endopodites 

liaA'e  separated  from  each 
^Jj  .,  other.  It  is  now  known,  how- 
ever,  that  they  really  repre- 
jj^a  sent  two  pairs  of  appendages 
which  have  lost  their  exopo- 
™°  dites  and  have  been  approxi- 
mated. The  anterior  pair  are 
small  plates  provided  with 
numerous  masticatory  setro  ou 
their  inner  edges,  and  are  the 
true  second  maxilhc,  while 
the  posterior  pair,  elongated 
and  limblike,  are  really  thorii- 
cic  limbs  and  so  may  l)o 
termed  maxillipeds.  Tli(> 
other  thoracic  appendages 
(<'-<')  are  typically  biramous 
and  serve  for  swimming. 

This  description  refers  to 
the  free-swimming  forms  ;  in 
parasitic  species  much  modi- 
fication of  the  a[»pen(higt's 
ensu(>s.  The  antennuhis  lose 
their  long  oarlike  character 
and  may  even  be  degenerated 
to  strong  hooks  wliich  serve 
to  fasten  the  animal  to  its 
host,  a  degeneration  whieh 
the  antennje  may  also  under- 
go. The  mouth-parts  beconu' 
Ml.—Calanua  hyperboreus  (after  adapted  to  a  piercing  func- 
tion, and  the  mandibles  mk^ 
represented  by  sharp  stylet- 
like  structures,  sometimes  eii- 
closed  in  a  tube  formed  by  the 

lips,    a   sucking-organ    being 
thus    produced.     The    tirst    nuixilho    undergo    consideralde 


Fio 

(JlKHDHKCHT). 

(ui,  =  iinus. 
aC  —  aiiU  liiiiilti. 
af  =  iintennii. 
mn  -  intuidililu. 
mx\  nix'  =  first  mid  sec-oiid  nmxilla' 
<'-<'  =  ihomcic  uppoiidiigcs. 


TYPE  CRUSTACEA. 


395 


Qdopodites 
rom  each 
lowu,  how- 
illy  repre- 
ppeudages 
leir  exopo- 
n  approxi- 
or  pair  are 
ided  with 
)ry  setro  on 
ud  arc  the 
Ihp,    while 

e  hi  11  gated 
sally  thoru- 
>  may  l)e 
Is.  T]i(> 
[)peiidages 

biraiuous 
luing. 
1  refers  to 
forms  ;  in 
inch  modi- 
;»l)eiula}j;es 
imiles  lose 

churact«n' 
egeiierntcd 
liich  serve 
lual  to  its 
ioii  whith 
lIho  uudei- 
rts  become 
reliig  fiiiic- 
idibles  jiiti 
arp  stylet- 
iietimes  eii- 
med  bv  the 

•J 

•gaii  beiiij^ 
iiiHiderahle 


reduction,  while  the  second  pair  is  frequently  adapted  to  form 
organs  for  adhering  to  the  host,  and  finally  the  thoracic 
appendages  may  undergo  various  stages  of  degeneration,  iu 
some  forms  entirely  disapjjearing. 

Branchial  organs  are  entirely  wanting  throughout  the 
order,  respiration  taking  place  over  the  entire  body  surface. 
A  heart  is  present  in  a  few  forms  (Calani(he)  consisting  of  a 
saclike  organ  with  but  a  single  pair  of  ostia,  but  in  the 
majority  of  cases  it  is  wanting.  A  single  median  eye  is  gen- 
erally present,  and  in  a  few  forms,  Pontella,  Corycceus,  and 
ArgidiiH,  lateral  eyes  are  also  present,  though  absent  as  a 
rule  throughout  the  group.  Each  lateral  eye  in  Corycanis 
consists  of  a  single  onimatidium,  but  in  Argnliis  is  compound 
and  similar  to  the  lateral  eyes  of  the  Brauchiopoda. 

The  Copepoda  are  throughout  bisexual  even  in  the  cases 
of  the  parasitic  forms.    The  vasa  defereutia  are  provided  with 
an  enlargement  in  which  the  spermatozoa  are  included  within 
a  capsule,  forming  a  spermatophore  which  during  copulation 
is  dei)()sited  in  the  neighborhood  of  the  female  genital  open- 
ing.    The  spermatozoa  being  discharged  from  the  spermato- 
])liore-capsule,  by  a  special  discharging  apparntus  with  which 
it  is  provided,  make  their  way  into  a  receptaculum    seminis 
which  communicates  with  each  oviduct,  the  ova  being  fertilized 
iluring   their    passage   to    the    exterior.     These  are    usually 
carried  iu  one  or  two  masses  attached  to  the  first  abdominal 
.segment  of  the  female,  though  in  some  forms,  such  as  NofotieJ. 
/)////.s',  they  undergo    their   development   in    a  brood-chamber 
formed  by  the  duplication  of  the  integument  of   the   dorsal 
surfaces  of  the  fourtii  and  fifth  thoracic  segments.     A  peculiar 
dimorphism  of  the  sexes  occurs  in  some  of  the  most  highly 
iiiodihed    parasites,   such    as   Chondvacanthun,   Achtheros,    and 
others,  the  male  being  very  much  smaller  than    the   female 
Jind  showing   much  less   degradation,  frecpieiitly  presenting 
Avrll-developed   eyes  and    more    or  less    perfectlv-developed 
.■ili|)endagef;,  «o  that  it  is  able  to  lead  for  a  time  a  free  exist. 
I'lii-e,     It  is  to  be  regarded  as  a  larval  stage  sexually  mature, 
sincir  it  resembles  clo.sely  the  female  when  in  the  sbige  immedi- 
ately before  fixation  to  its  host,  tiie  greater  ])art  of  the  (leirpn. 
e  after  that  has  been  acco 


■lir 


sib:; 


■51 


1' 


Two  suborders  are  recognizable. 


ipliubt 


m 


396  INVERTEBRATE  MORPHOLOGY. 

1.  Suborder  Eucopepoda. 

This  suborder  iucluJes  the  majority  of  the  Copepoda,  and 
its  members  are  characterized  by  having  only  tlie  first  thoracic 
segment  fused  with  the  head  and  by  possessing  usually  a 
well-developed  abdomen.  Many  are  free-swimming,  some  in- 
habiting fresh  water,  as  Cyclops  and  Canthocamptus,  while 
others  are  more  especially  marine,  such  as  Ilarpacticus,  Valamis 


nix« 


Fig.   178.—^,   Philirhthyfi  xiphin  seen  from  the  nonsAt,  Surface  (nfi.T 
C'LAfs);  li,  Acfilfieres  percarum  (fiom  Bkonn). 

(Fig.  177),  find  Cetochihis,  the  latter  sometimes  occurring  in 
enormous  schools,  and  forming  an  important  food-supply  for 
fish  and  the  baleen  whales.  Some,  on  the  other  hand,  lead  a 
commensalistic  life,  occurring  in  the  branchial  chamber  of 
Tunicates,  e.g.  Noiixh'Jphijs,  while  a  large  number  of  forms  are 
])arasitic.  The  degree  of  parasitism  varies  greatly  in  dirtercnt 
forms  ;  thus  many  are  ca))ablo  of  free  existence,  beconiini^ 
parasitic  only  occasionally,  such  naCori/avm  and  tlie  brilliantlv- 
c(jlored  Sttpphin'uu,  while  others,  such  as  h)y(i.sihis,  ])arasitic 
on  the  gills  of  fislies,  and  Cnh'yus  and  Pduddru/i,  though  essou- 


epoda,  and 
rst  thoracic 
5  usually  a 
ig,  some  iu- 
ptus,  while 
'ius,  Calamis 


TYPE  CHUSTACEA. 


397 


lUnFACE    (nfi.T 

.^curriug  in 
-supply  for 
aud,  lead  a 
jhamlxM'  of 
f  forms  arc 
in  dirteroiit 
,  becoiniiii,' 
brilHaiitly- 
iH,  ])arasitic 
rnigh  essen- 


tially parasitic,  still  retain  more  or  less  perfectly  the  segmen- 
tation and  general  appearance  of  free-swimming  forms,  the 
modifications  which  they  have  undergone  affecting  principally 
the  antennae,  which  are  modified  for  purposes  of  adhesion  to 
the  host,  the  mandibles,  which  are  piercing  organs,  and  in  some 
cases  the  maxillre,  which  may,  like  the  antennjB,  become  hook- 
like. Frequently,  however,  the  body  assumes  aberrant  forms, 
as  in  Philichthys  (Fig.  178,  A),  aud  the  segmentation  may  en- 
tirely disappear,  as  in  Penella,  Lerncea,  Chondr acanthus,  Achtheres 
(Fig.  178,  /?),  and  Anchorella,  these  last  two  forms  presenting 
a  peculiar  modification  of  ...le  second  maxilhe  in  the  females, 
the  two  appendages  fusing  at  their  tips  to  form  a  chitinous 
adhesive  disk  which  serves  as  an  organ  of  adhesion.  In  the 
majority  of  these  forms,  as 
already  noted,  the  thoracic 
appendages  may  become  more 
or  less  rudimentary;  indeed 
even  in  the  less  modified 
forms,  such  as  Erqamlu.s,  the 
appendages  of  the  fifth  thora- 
ic  segment  may  be  wanting. 


nix 


3.  Suborder  Branclnura. 

In  the  Branchiura  the 
cephalic  and  thoracic  seg- 
ments are  fused  together  to 
form  a  shield-shaped  ce})halo- 
tliorax,  while  the  abdomen  is 
small  and  divided  into  two 
platelike  halves  which  have 
a  rich  blood-suppl}',  appar-  ^^^-  '^"^^■—Arpnlim  foliaceua  (after 
ontly  serving  resi)iratory  ])ur-.  „<,  ^  amrnllles. 

poses,    and     in     the     males  l  =  di>resiive  glaud. 

contain  the  testes.  wa;  =  second  muxilla. 

The  basal  joint  of  the  an-  '"'=  '*>'''• 

tennules  (Fig.  i7(>,  at')  is  devel-  '  "  ^''"''• 

oped  into  a  strong  hooked  process,  aud  the  mandibles  and 


12 
-SI 


tirst  maxillo),  which   are    stylet-like,  are    enclosed 


lU  a 


tube 


}  I 


398 


INYERTEBRATE  MORPHOLOGY. 


iormed  by  the  fusion  of  the  upper  aud  lower  lips.  The 
second  maxillse  {mx)  develop  at  their  bases  large  suckers, 
while  the  first  thoracic  ai)pendages,  here  termed  maxilli- 
peds,  are  limblike  aud  have  also  hooked  processes  upon  the 
basal  joints.  These  are  succeeded  by  four  pairs  of  biramous 
swimming  appendages. 

A  well-developed  heart  is  present,  giving  rise  to  arteries 
extending  throughout  the  length  of  the  body.  A  pair  of 
lateral  compound  eyes  {oc)  are  also  present,  and  a  further 
difterence  from  the  majority  of  the  Eucopepoda  lies  in  the 
fact  that  the  eggs  are  not  carried  by  the  female,  but  are  de- 
posited on  foreign  bodies. 

All  the  forms  are  parasitic,  in  some  cases,  as  Argulus, 
upon  fresh-water  fishes,  but  they  also  possess  the  power  of 
swimming  actively. 

4.  Order  Girrhipedia. 

The  Girrhipedia  or  Barnacles  are  without  exception  ma- 
rine forms,  and  in  the  adult  condition  either  adhere  to  foreign 

P. 


Fig.  180.— Cypuis  Larva  of  Lepas  (a.ner  Cumb). 
Ah  —  abdoiiR'n.  Oc  =  eye. 

AV  =  iiutennuk's.  Ov  =  ovary. 

Cg  =  duct,  of  cement-gland.  p  =  penis. 

0  =  opeuinjr  of  oviduct.  2'''  =  third  tborncic  foot, 

bodies,  leading  a  ])erfectly  sessile  life,  or  olse  bore  in  the  slioll^^ 
of  certain  Mollusca,  or  finally  are  parasitic.  It  will  be  con- 
venient to  describe  first  of  all  the  organization  of  the  HcsHilc 
and  boring  forms,  later  considtu-ing  briefiy  the  parasitic  forms 
which  show  many  peculiarities  due  to  degeneration, 
course  of  de^ 


[•ing 


'P 


ipe( 


P 


through  a  larval  stage  similar  in  general  appearance  to  .in 


TYPE  CHUSTACEA. 


399 


ips.  The 
;e  suckers, 
d  maxilli- 
3  upon  the 
t  biramous 

to  arteries 
A  pair  of 
a  further 
ies  iu  the 
)ut  are  cle- 

s  Argulm, 
5  power  of 


sption  ma- 
to  foreign 


foot. 

the  she]l>< 
11  be  con- 
he    HCS.Hilc 

iitic  forms 

ia  all  pass 
lice  to  iiii 


OstracoJe  and  hence  termed  the  Cypris-stage  (Fig.  180). 
The  body  is  enclosed  in  extensive  folds  of  the  body-wall 
termed  the  mantle,  and  the  antenuules  {at')  are  characterized 
by  being  directed  forwards  and  terminating  in  an  adhesive 
<lisk  upon  which  open  the  ducts  of  cement-glands.  Adher- 
ing to  a  foreign  body  by  these  disks,  the  adhesion  being 
made  permanent  by  the  secretion  of  the  glands,  a  rotation  of 
the  body  upon  the  anteunse  through  90°  takes  place,  so  that 
the  animal  comes  to  lie  upon  its  back,  the  ventral  surface 
looking  away  from  the  point  of  fixation.  The  antennules 
persist  as  rudimentary  structures,  and  the  adult  animal  really 
seems  to  be  fixed  by  the  dorsal  surface  of  the  head,  which 
may  elongate  to  form  a  stalk  bearing  the  body  proper  at  its 
extremity  {Lepas,  Fig.  181). 

The  body  shows  no  indication  of  segmentation,  but  a  head 
region  may  be  distinguished  from  the  thorax  and  this  from  a 
short  abdomen  by  means  of  the  appendages.  The  character 
of  the  antennules  has  already  been  mentioned;  the  anteiime 
are  wanting  in  adults,  and  the  mandibles  and  first  maxilhe 
are  simple  toothed  plates  destitute  of  palps,  while  the  second 
juaxilhe  are  small  and  fused  together  to  form  a  kind  of  lower 
lip.  The  thoracic  appendages  (Fig.  181,  B)  are  biramous,  the 
l)asal  i)ortion  supporting  two  long  multiarticulate  and  usually 
setose  filaments.  In  typical  cases  six  pairs  of  these  app',;ud- 
ages  occur,  but  they  may  be  reduced  to  four  {Alcippe)  or 
three  pairs  {Cn/pfophiahi.s).  In  the  living  animal  flexions  of 
these  appendages  towards  the  ventral  surface  of  the  body 
take  place  almost  rhythmically,  currents  of  water  being  thus 
impelled  towards  the  mouth  together  with  any  food-particles 
they  may  contain.  The  abdomen  does  not  bear  appendages, 
Init  from  it  arises  a  long  slender  cirrus  (Fig.  181,  />*,  cir)  which 
contains  the  terminal  })ortions  of  the  vasa  defereiitia. 

The  mantle-folds  which  occur  in  the  Cypris-larva  persist 
in  the  adult,  and  calcification  of  their  walls  takes  place,  giving 
lise  to  a  calcareous  shell,  composed  of  several  pieces,  which 
encloses  the  animal.  In  the  genus  Lepus,  the  goose-barnacle, 
this  shell  consists  of  five  ])ieces.  On  the  dorsal  side  there  is 
a  single  unpaired  piece  which  receives  the  name  of  the  carhia 
(Fig.  181,  ^1,  C(i)') ;  at  the  sides  and  resting  below  cm  the  uppar- 


::» 

"'"1 

f"  '-•Si ' 

.If— •- 

.■..3iCJ 
'^'"^ 

-'35 


400 


INVEHTEBRATE  MORPHOLOGY. 


most  part  of  the  stalk  are  the  two  acuta  (sc),  while  above 
these  are  the  terga  {te),  also  paired,  the  opening  into  the  in- 
terior lying  between  the  terga  and  the  scuta  of  opposite  sides. 
In  Scalpellmn  between  the  two  scuta  a  sixth,  unpaired,  piece, 
the  rostrum,  is  inserted,  and  in  the  same  genus  between  the 
scuta,  terga,  and  carina  and  the  summit  of  the  stalk  small 
accessory  pieces  occur ;  and  if  one  imagines  a  disappearance 


Fig.  \?>1.—Lepas  fascicular  is.    A,  exterior;  "  "•'icture. 


ag  =  antemiary  gland. 
Car  =  cariim. 
Cir  =  cirrus 
M  —  shell -muscle. 
Od  =  oviduct. 


Ov  —  ovary 
pe  =  peduncle. 
Sc  =  scutum. 

t  =  testis. 
Te  —  tergum. 
Vd  =  vus  deferens. 


of  the  stalk  of  such  a  form,  an  enlargement  of  these  accessory 
pieces,  usually  six  in  number,  and  their  articulation  to  form 
a  wall-like  circle  around  the  body  of  the  animal,  the  scuta 
and  terga  closing  it  in  and  forming  as  it  were  a  roof,  an  idea 
of  the  arrangement  of  the  shell  of  Balanus,  the  acorn-barnacle, 
will  be  obtained. 

No  special  respiratory  organs  exist,  the  entire  surface  of 
the  body  probably  performing  this  function,  nor  does  a  heart 
seem  to  occur   in  any  member  of  the  group.     The  nervous 


TYPE  CRUSTACEA, 


401 


die  aboA'e 
bo  the  iu- 
site  sides, 
ed,  piece, 
tweeu  tlie 
alk  small 
)pearauce 


accessory 
a  to  form 
the  scuta 
f,  au  idea 
•baruaele, 

urface  of 
3S  a  heart 
}  uervouii 


system  consists  in  Lepas  of  a  syncerebrum  and  five  or  six 
ventral  ganglia, — of  which  the  last  is  probably  composed  of  at 
least  two  fused  ganglia,  and  a  certain  amount  of  fusion  has 
also  probably  occurred  in  the  first.  In  Balamis  the  fusion 
has  reached  its  greatest  extent,  the  entire  ventral  chain  of 
ganglia  having  fused  to  a  ringle  mass.  The  median  unpaired 
eye  is  usually  represented,  and  in  some  forms  rudimentary 
lateral  eyes  are  present,  showing,  however,  a  marked  degen- 
eration from  the  large  compound  eyes  which  occur  in  the 
Cypris-like  larva. 

As  a  rule  the  Cirrhipedia  are  hermaphrodite  in  accord- 
ance with  their  sessile  or  parasitic  life.  The  testes  (Fig. 
181,  B,  t)  lie  one  on  each  side  of  the  digestive  tract,  and  the 
vasa  deferentia  {vd)  after  dilating  into  seminal  vesicles  pass 
to  the  long  cirrus  (cir)  borne  by  the  abdomen,  at  the  tip  of 
which  they  open  by  a  short  common  duct.  The  ovaries  lie 
in  Lepas  (Fig.  181,  B,  ov)  in  the  stalk,  and  in  stalkless  forms, 
such  as  BaUinus,  in  the  basal  fold  which  corresponds  to  the 
stalk,  and  the  oviducts  {od)  passing  upwards  and  then  back- 
wards open  on  the  basal  joints  of  the  anterior  thoracic  ap- 
pendages. Although  hermaphroditism  is  the  rule  throughout 
the  order,  yet  in  some  cases  small  males  have  been  found 
which  have  received  the  name  of  "  complemental "  males. 
These  occur  in  the  genus  Ihla  and  in  some  species  of  Sccdpel- 
liim  and  live  like  parasites  in  folds  of  the  mantle  of  the  her- 
maphrodite forms.  In  form  they  do  not  advance  greatly 
beyond  the  Cypris  stage,  and  possess  in  addition  to  the  anten- 
uules  only  four  pair  of  small  thoracic  limbs,  the  mandibles  and 
maxilLe  as  well  as  the  mouth  being  entirely  wanting,  while 
the  digestive  tract  is  rudimentitry.  In  other  species  of  Seal- 
pellupi,  and  in  the  genera  Alcippe.  and  Cri/pfopJiialus,  these 
pigmy  males  are  also  present,  but  the  forms  in  which  they 
live  are  no  longer  hermaphrodites  but  females,  so  that  bi- 
sexuality  with  sexual  dimorphism  occurs  in  these  forms, 

It  might  be  supposed  from  the  u;ener.al  occurrence  of  Ijisexuality  ainoiig^ 
the  Crustacea  that  these  last  cases  represented  the  first  stage  in  the  dis- 
appearance of  the  males,  leading  finally  to  hermaphroditisiu.  Since,  how- 
ever, Alcippe  and  Cri/pti)phialus  are  tlie  most  degenerate  of  the  Cirrhi- 
peds  so  far  discussed,  it  would  seem  that  this  is  not  the  case,  but  rather 


403 


INVERTEBRATE  MORPHOLOGY. 


1 

4 


that,  on  the  assumption  of  a  sessile  life  berraaphroditism  became  character- 
istic of  the  order,  the  bisexualism  of  these  boring  forms  l^eing  secondarily 
acquired.  The  fact  that  the  pigmy  males  present  larval  characters  sug- 
gests the  idea  that  their  occurrence  may  be  an  extreme  case  of  proterandry. 
If  in  the  hermaphrodite  forms  it  is  a  rule  that  the  spermatozoa  mature 
earlier  than  the  ova,  thus  preventing  self-fertilization,  it  is  conceivable  that 
this  early  maturation  of  the  testes  might  be  carried  back  almost  to  the 
Cypris  stage  and  pigmy  males  be  thus  developed. 

Not  uufrequeiitlj  barnacles  choose  the  bodies  of  other 
animals  upon  which  to  fasten,  as  for  instance  upon  the  cara- 
pace of  Limulus,  or  on  the  skin  of  whales,  and  the  genus 
Anelasma  fastens  itself  upon  the  surface  of  the  body  of  a 
Shark,  its  stalk  penetrating  into  the  tissues  and  developing 
rootlike  processes  and  so  enabling  it  to  lead  a  parasitic  life. 
As  a  result  of  this  the  calcareous  plates  cease  to  develop, 
the  niantle  having  merely  a  leathery  consistency  and  the 
mandibles  and  maxillcB  remain  rudimentary.  This  degenera- 
tion is  carried  still  further  in  Proteolepas  (Fig.  182),  which 

lives  as  a  jJarasite  in  the 
mantle-cavity  of  other  Oir- 
rhipeds  and  has  a  maggotlike 
appearance,  the  body  being 
distinctly  divided  into  eleven 
segments  and  lacking  all 
traces  of  a  mantle.  The 
mouth-parts  are  modified  so 
as  to  be  suctorial,  and  the 
thoracic  feet  are  entirely 
wanting,  while  the  digestive 
tract  becomes  rudimentary. 
Finally,  a  group  of  forms, 
known  as  the  liJdzocepJiala,  fasten  themselves  to  the  abdomen 
of  crabs  and  become  transformed  into  cylindrical  or  saclike 
structures  entirely  destitute  of  digestive  tract  and  appendages, 
rootlike  processes  arising  from  the  anterior  end  of  the  body 
and  traversing  the  body  of  the  host,  by  whose  juices  the 
parasite  is  nourished.  The  genus  SaccuUna  consists  of  an  an- 
terior short  cylindrical  portion  from  the  extremity  of  Avhich 
the  rootlike  processes  arise  and  which  perforates  the  integu- 
ment of  the  host.     From  the  base  of  this  a  circular  fold  arises 


Fig.  183. — Proteolepas  (from  Bronn). 

in  =  muscle. 

ov  =  ovar}'. 

vs  =  vesicula  seminalis. 


le  character- 
secondarily 
racters  siig- 
)roterandry. 
•zoa  mature 
eivable  that 
nost  to  the 

of  other 
the  caia- 
he  gemis 
oclj  of  a 
evelopiug 
isitic  life, 
develop, 
and   the 
legeuera- 
2),  which 
!    ill    the 
her    Oir- 
aggotlike 
:ly    being 
to  eleveii 
king     all 
e.       The 
dified  so 
and    the 
entirely 
digestive 
uieutaiT. 
if    forms, 
abdomen 
r  saclike 
•eudages, 
the  body 
lices  the 
of  an  au- 
of  which 
J  integu- 
Id  arises 


TYPE  CRUSTACEA. 


403 


which  encloses  between  its  walls  and  the  wall  of  the  body  a 
cavity  which  serves  as  a  broo'l-pouch  and  communicates  with 
the  exterior  by  a  terminal  opening  capable  of  being  closed  by 
a  sphincter.  The  body  proper  contains  only  the  nervous 
system,  reduced  to  a  single  ganglion,  and  the  ovaries  and  the 
paired  testes,  as  well  as  a  pair  of  cement-glands  connected 
with  the  female  genital  openings. 

The  development  of  Saccidiiia  presents  some  extraordinary  features. 
It  resembles  in  its  early  stages  the  develupment  of  the  other  Cirrhipeds 
and  reaches  a  typical  Cypris  stage  during  which  it  fastens  itself  by  the 
anteiinuk's  to  the  body  of  a  crab.  The  tissues  of  the  larva  then  retract 
lliemselves  from  the  cuticle,  and  a  remarkable  degeneration  of  the  body 
together  with  an  amputation  of  the  entire  thoracic  and  abdominal  regions 
then  ensues,  leaving  an  oval  mass  of  tissue,  richly  pigmented,  attached  to 
the  body  of  the  crab  by  the  empty  cuticle  of  the  antennules.  At  the 
anterior  end  of  this  mass  a  hollow  dartlike  process  arises  which  is 
l)uslied  forward  through  the  hollow  cuticle  of  the  antennules  and  pierces 
the  body-wall  of  the  host,  the  parasite  apparently  flowing  then  through  the 
dart  and  so  becoming  an  endoparasite.  Within  the  body  of  the  crab  the 
development  of  the  Saecidina  takes  place  from  the  apparently  undiffer- 
entiated mass  of  tissue  by  which  it  is  represented,  and  growing  rapidly 
produces  an  absorption  of  the  ventral  integument  of  the  host,  which  allows 
the  saclike  body  to  protrude  to  the  exterior.  It  is  to  be  noted  that  para- 
sitic Cirrhipeds  (Laura)  have  been  found  in  the  stem  of  a  Gorgonian  and 
also  in  the  body-cavity  of  Echinoderms  {Dei id rog aster).  These  forms 
show  many  peculiarities  of  structure  and  have  been  grouped  together  iu 
the  suborder  Ascothoracida. 

II.  Class  Malacostraca. 

The  Malacostraca  are  distinguished  from  the  Entomo- 
straca  by  the  definiteness  throughout  the  entire  class  of  the 
number  of  metameres  entering  into  the  composition  of  the 
body.  The  head  consists  of  five  segments  which  are  invari- 
ably fused,  and  the  thorax  is  composed  of  eight,  of  which  the 
anterior  one,  or  indeed  all,  may  unite  with  the  head  to  form 
a  perfect  or  imperfect  cephalothorax.  The  abdomen  is  the 
onl}'  region  in  Avhich  variation  of  number  takes  place,  and 
this  variation  is  confined  to  a  single  group  of  forms  (Lepto- 
straca).  In  these  the  abdcnnen  is  composed  of  eight  segments, 
while  in  all  other  forms  it  possesses  only  seven,  counting  iu 
both  these  cases  the  terminal  segment  which  bears  the  anus 


•mi 

8S» 

wtuS 

J:* 

IBS;; 

It*-'— 


3 

r 


404 


IN  VERTEBRA TE  MORPHOLOG  Y. 


and  is  known  as  the  telson.  All  these  segments  with  the 
exception  of  the  telson,  and  in  the  Leptostraca  of  the  seg- 
ment immediately  in  front  of  it,  bear  appendages.  Folds  of 
the  integument  forming  a  eephalothoracic  carapace  are  fre- 
quently present,  but  it  is  rare  that  a  bivalved  shell  occurs. 

The  stomach  is  always  provided  with  chitinous  tteth  and 
forms  an  efficient  masticatory  organ,  and  lateral  eyes  are 
present  except  in  some  Cumacea  and  in  some  forms  belong- 
ing to  other  groups  which  inhabit  caves  or  the  depths  of  the 
ocean,  under  which  conditions  the  eyes  become  rudimentary. 
The  openings  of  the  female  reproductive  organs  are  always 
situated  on  the  basal  joints  of  the  appendages  of  the  sixth 
thoracic  segment,  and  the  male  openings  on  the  appendages 
of  the  eighth  segment.  The  antennary  gland  is  usually  well 
developed,  while  the  shell-gland  is  either  rudimentary  or 
wanting  in  the  adult. 

Although  numerous  rather  small  forms  belong  to  this 
class,  yet  on  the  whole  they  much  surpass  in  size  the  Ento- 
mostraca,  some  forms  even  reaching  a  length  of  over  50  cm. 
A  few  forms,  such  as  Euphamia  and  Fenams,  leave  the  egg  as  a 
Nauplius,  but  in  the  majority  this  stage  is  passed  before 
hatching,  the  embryo  first  leading  a  free  existence  at  a  later 
Btage  in  the  larval  form  known  as  the  Zijea,  though  in  some 
cases  hatching  may  be  retarded  until  later  stages,  in  fact 
sometimes  until  the  adult  form  is  acquired. 


I.  Subclass  Leptostraca. 

The  Leptostraca  are  exceedingly  interesting  forms,  present- 
ing similarities  to  the  Entomostraca  on  the  one  hand  and  to 
the  Malacostraca  on  the  other,  thus  connecting  the  two 
classes.  They  are  exclusively  marine  in  habitat  and  possess 
a,  thin  bivalved  shell- duplicature  which  is  provided  with  an 
adductor  muscle  and  is  prolonged  in  front  into  an  unpaired 
plate  which  covers  the  dorsal  surface  of  the  head. 

The  antennules  (Fig.  183,  at')  consist  of  a  three-jointed 
basal  portion  bearing  in  addition  to  the  multiarticulate  fiagel- 
lum  a  scalelike  exopodite,  a  structure  wauling  in  the  anteuutu 
(af),  which  otherwise  have  a  similar  form.     The  mandil'os 


TYPE  CRUSTACEA. 


405 


witli  the 
f  the  seg- 

Folds  of 
B  are  fre- 
Dccnrs. 
tteth  aud 

eyes  are 
is  beloug- 
ths  of  the 
imeutary. 
re  always 
the  sixth 
peiidages 
lally  well 
Biitary  or 

;  to  this 
lie  Euto- 
sr  50  cm. 
J  egg  as  a 
d  before 
it  a  later 
in  Some 
;,  in  fact 


,  pre  sen  t- 
d  aud  to 
the  two 
1  possess 
i  with  an 
unpaired 

e-jointed 
,te  flagel- 
antenn.u 
landil'os 


bear  a  palp,  as  do  also  the  first  maxilhe,  it  being  in  these  latter 
appendages  prolonged  into  a  long  slender  limblike  {mx) 
structure  which  is  directed  dorsally  and  serves  for  cleansing 
the  inner  surface  of  the  shell.  The  second  maxillfo  are 
biraraous  foliate  structures,  as  are  also  the  eight  thoracic 
appendages  {t),  each  of  which  bears  upon  its  basal  joints  a 
platelike  epipodite  which  is  respiratory  in  function.  The 
four  anterior  abdominal  appendages  {ah*)  are  strong  biramous 
swimming-legs,  while  the  two  posterior  are  small  aud  unira- 
mous.      Behind  the  last  appendage-bearing  segment  are  two 


sm  nix 


Fig.  1%^.—Nehalia  Oeoffroyi,  Male  (after  Clacs). 
ab*  =  abdominal  appendage.  Ji  =  heart. 

adr  =  antennary  gland  mx  =  process  of  first  miixilla. 

ae  =  antennule.  sm  =  shell-muscle. 

a(^  =  antenna.  t  =  thoracic  appendage. 

te  =  testis. 

others  without  appendages,  the  terminal  one  being  the  telson, 
the  Leptostraca  possessing  one  more  metaraere  than  the  rest 
of  the  Malacostraca. 

The  heart  is  an  elongated  organ  extending  from  the 
maxillary  region  as  far  back  as  the  fourth  abdominal  seg- 
meut ;  it  possesses  several  ostia,  and  is  prolonged  anteriorly 
iiiid  posteriorly  into  aortre.  The  antennary  gland  is  present 
aud  a  rudimentary  shell-gland  also  persists.  The  lateral  eyes 
are  borne  upon  short  stalks. 

The  group  contains  but  few  species,  the  majority  belong- 
ing to  the  genus  Nehidia  (Fig.  183). 


Mil,. 

•llir 
■»•. 

1% 

■I? 

•iS;: 


■s. 


406 


INVERTEBRATE  MORPHOLOGY. 


II.  Subclass  Thoracostraca. 

The  Thoracostraca  are  characterized  by  the  occurreuce 
throughout  the  group  of  a  well-developed  duplicature  of  the 
body-wall,  arising  from  the  posterior  head-segmeuts  aud 
covering  iua  greater  or  less  uumber  of  the  thoracic  segments, 
constituting  what  is  termed  a  cara])ace.  On  the  dorsal  sur- 
face it  fuses  Avith  the  body-wall,  but,  at  the  sides  encloses  a 
respiratory  chamber  in  which  the  branchiic,  when  present,  lie. 
According  as  the  carapace  extends  over  all  or  only  over  the 
anterior  thoracic  segments  a  mf)re  or  less  perfect  ce})hal()- 
thoi-ax  is  formed,  a  fusion  of  the  covered  thoracic  segments 
with  each  other  and  with  the  head-segments  occurring,  the 
abdominal  segments  remaining  in  all  cases  distinct. 

Branchia>,  consisting  of  bunches  of  hollow  thin-walled 
processes  whose  cavities  communicate  with  the  lacunar  spaces 
of  the  body,  are  borne  by  certain  of  the  appendages  except  in 
the  Mysidea'.  The  lateral  eyes  except  in  the  Cumacea  are 
stalked  and  the  autennary  gland  is  usually  well  developed. 


1.  Order  Schizopoda. 

The  carapace  in  the  Schizopoda  covers  in  the  entire 
thorax,  but  a  certain  number  of  the  posterior  thoracic  seg- 
ments remain  ununited  with  it.  The  antenuules  are  biru- 
mous,  as  are  also  the  antenuse  (Fig.  184),  tiie  exopodite  iu  the 
latter  case  being  represented  by  a  scalelike  structure.  Tho 
Liioracic  appendages  are  all  similar  and  are  biramous,  the 
endojjodites  being  limblike  structures  tip])ed  by  claws, 
while  the  exo])odites  are  multiarticuhite  tiagelhi.  In  tlie 
genus  A)(phan.si(i  the  two  last  ))airs  are  quitu  rudimentary, 
their  brauchia'  remaining,  however,  well  develoj^ed.  The  two 
anterior  pairs  iu  the  genus  7l///.s/.s'  have  their  basal  joints  en- 
larged to  form  jaws  and  cousecpiently  are  distinguished  as 
maxilliiKHls,  but  in  Euphnmut.  this  distinction  does  not  occur. 
The  abdominal  a[)[)endages  in  the  females  are  generally  small 
with  tlio  exception  of  the  sixth  j)air,  and  in  the  genus  il///.s/v 
are  quite  rudimentary.  In  the  mah»s  of  all  genera  tliey  arc, 
liowever,  well-developed  bii-amous  swimming-f('(»t,  and  tln' 
sixth  pair  iu  both  sexes  forms  witli  the  telscjn  a  tail-iiu. 


TYPE  CRUSTACEA. 


407 


Braucliise  are  present  in  3Iysis  only  in  the  form  of  small 
epipodiul  elevations  of  the  thoracic  appendages,  and  in  Siriella 
as  coiled  tubular  structures  on  the  protopodites  of  the  abdom- 
inal appendages  of  the  males.  In  Euphamia,  however,  they 
form  large  ramified  bunches  attached  to  the  protopodites  of 
the  thoracic  limbs  and  are  present  even  on  the  rudiments  of 
the  seventh  and  eighth  pairs  ;  they  are  not,  however,  enclosed 


Fig.  184. — Mysis  relicta  (after  Sars). 
hp  —  biood-poucb.  ot  =  otocyst. 

within  a  chamber  formed  by  the  lateral  portions  of  the  cara- 
pace, but  project  freely  to  the  exterior. 

Otocysts  occur  in  the  inner  lamelLe  of  the  sixth  abdominal 
appendages  (Fig.  184:,  ot),  and  in  Kuphansla  a  number  of  eye- 
like phos})horesceut  organs  occur  on  the  basal  joints  of  the 
second  and  seventh  thoracic  appendages  as  well  as  upon  the 
ventral  surface  of  the  four  anterior  abdominal  segments. 
They  are  spherical  in  shape  and  each  consists  of  a  cup  of 
cells  containing  red  pigment  covered  in  by  a  lens. 

The  Schizopoda  are  essentially  marine,  though  some 
species  of  the  genus  Mysis  (Fig.  IBl)  occur  in  fresh  and 
brackish  water. 


«!5 


tSS;: 


'5:30 


■?. 


2.  Order  Gumacea. 

In  tliis  order  the  carapace  covers  only  the  anterior  three 
or  four  thoracic  segments,  five  or  four  of  them  remaining  dis- 
tinct. The  antennules  are  short  and  in  the  male  biramous, 
while  the  antennie,  though  in  the  female  almost  rndimentarv, 
may  be  as  long  as  the  entire  body.  The  two  anterior  thoracic 
■ippendages  form  nnixillipeds,  their  basal  joints  serving  for 
niasiicntion  while  the  succeed 


ling 


V 


)like,  all 


hilt  the  last  or  three  last  possessing  snuill  exopodites.     The 


408 


IN  VKHTEBItA  TE  MORPIIOLOG  Y. 


sixth  abdomiual  segment 
bears  a  pair  of  biramous  ap- 
pendages with  a  long  single- 
jointed  protopodite,  the  re- 
maining segments  being  in 
the  female  destitute  of  ap- 
pendages, but  in  the  male  the 
anterior  2  {DiastyUs),  3,  or  5 
{Campylaspis)  segments  may 
bear  biramous  swimrning-feet. 

The  lateral  eyes  are  never 
stalked  and  may  be  closely 
approximated  or  even  fused 
on  the  dorsal  surface  of  the 
cephalotliorax.  They  uro 
generally  composed  of  but 
few  omniatidia  and  in  some 
species  are  entirely  wanting. 

The  Cumacea  are  exclu- 
sively marine  and  are  more 
especially  characteristic  of 
the  colder  seas. 

3.  Order  Stomatopoda. 

As  in  tln)  Cumacea  tlir 
carapace  covers  oidy  some  of 
the  anterior  thoracic  seg- 
ments, the  last  three  or  four 
remaining  distinct,  but  tlif 
abdomen,  instead  of  boiiiLr 
slender,  is  even  stouter  tliaii 
th(i  tliorax  and  ends  in  a  ter- 
minal   tail-tin.     The   anterior 

.    -,  portion  of  the  head,  bearint,' 

Pio.  \Hry. —Dtasii/hn  sfygtn,  Mai,k  (oftor  '  1,1/ 

HARsfroniLANo).  the  eyes    and    the   two    ])itirs 

«,  =  (uitciiimlc.         «'«  =  eii(l()|)o(lito.       of  autenuie,  is  separated  from 

M.=:llllt(!l)Da.  t'JJriL'XODoditL'.  ,  ,    ,  ..  ,        .. 

aft=iil)(lominRlnp       ?)  =  iil)(r()miiml  up-  «"hI  movabie  iipoii  Ihf  ThmI  ul 


cl/i= 


p.-n(luj?oH.     ,„  „,,l'«''"l'ws-      the  cephulo-thorax,  and  onlv 
=  cumimcc.  Il-l III  =  thovnilv.  .,  '  ..,,•" 


st'giiicnis,      the    more    anterior    thoracis' 


TYPE  CliVSTACEA. 


409 


segment 
amous  ap- 
>ug  siugle- 
3,    the    re- 

beiug  iu 
ite  of  ap- 
e  male  the 
is),  3,  or  ") 
leuts  may 
imiug-feet. 
\  are  never 
be  closely 
sven  fuse<l 
ace  of  the 
Cliey  are 
id  of  but 
tl  in  some 
,'  wanting, 
are   exclu- 

are  more 
;eristic     of 


topoda. 

macea   the 
ly  some  <»f 


racic 


sen 


ee  or  four 
;,  but  tlic 
of  beinu' 
Duter  than 
Is  in  a  ter- 
10  anterior 
id,  1[)eariii.t,' 

two  ]))iirs 
rated  from 

tilt!  vest  <it 
:,  and  only 
r    thnracii' 


segments  are  fused  with  the  carapace,  though  it  covers  in 
several  others. 

The  antennules  consist  of  an  elongated  three-jointed  basal 
portion  bearing  three  many-jointed  tiagella,  while  the  anten- 
n.^  are  generally  shorter,  the  exopodite  being  represented  by 
a  large  scale.  The  maxillse  are  comparatively  small,  and  the 
appendages  of  the  five  anterior  thoracic  appendages  are 
crowded  forwards  and  are  termed  maxillipeds,  being  limb- 
like  structures  destitute  of  exopodites,  but  possessing  well- 
developed  epipodites,  and  with  the  terminal  joint  capable  of 
liexion  upon  the  next  succeeding  one.  The  second  maxilli- 
ped  IS  especially  long  and  large,  and  with  its  strong  terminal 
and  penultimate  joints  forms  a  very  efficient  weapon  fen-  secur- 
ing prej.     The  three  posterior  appendages  of  the  thorax  are 


Fig,  \%i\.—Squilla  mantis  ffmm  T.et'nis). 
a'  =  anteumiles.  p^  ^  iDuxillipedg 

a^  =  anteiiiiDB.  p  =  tl.omcic  limbs. 

oc  =  compound  eyes.  pa  =  ubdomiiml  liml,s. 

slender  biramous  structures,  the  somewhat  stronger  abdomi- 
nal api>endageH  being  also  biramous  and  somewhat  lamellar 
swimming-feet.  The  last  pair  are  especially  enlarged  and  di- 
rected backwards,  forming  with  the  telson  the  strong  tail-fin 

Bunches  of  branchial  filaments  occur  upon  the  outer  lamel- 
1m>  ol  the  abdominal  appendages  with  the  exception  of  the  last 
])air.  The  heart  is  much  elongated,  extending  from  the  ante- 
rior thoracic  region  as  far  back  as  the  fifth  abdominal  seg. 
i.ient  and  i)ossessing  numerous  pairs  of  rstia.  It  is  prolon-tnl 
.•u.toriorly  and  posteriorly  into  aortro  and  gives  off  laterally 
lu  each  segment  a  ])air  of  avtia-ies. 

The  Stomatopods  are  all  marine  and  pass  through  a  com- 


l>lioated 


tl 


Kvnm  oi  ni«iam»»rpii().s«!s  during  development.     S 


( 


I  mux 


principal  genera  are  SquUla  (Fig.  IHii),  Ly.iosqnilla 
f  defy  Iks, 


ome 
and 


imp 

Mix 
"HA 


I 


410 


IN  VERTEBRA  TE  MORPIIOLOG  Y. 


4.  Order  Decapoda. 


lu  the  Decapods  the  carapace  is  well  developed,  covering 
in  the  thorax  completely  (Fig.  1G2),  the  segmeutsof  that  region 
of  the  body  fusing  with  ii  dorsally,  so  that  a  perfect  cephaio- 
thorax  is  present.  The  autennules  generally  possess  two 
terminal  multiarticulate  flagella,  and  the  antenuie  frequently 
lack  the  scalelike  exopodite  which  occurs  in  other  groups 
(e.g.,  Schizopoda).  In  the  second  maxilliTe  the  exopodite  is 
transformed  into  a  platelike  structure  which,  swinging  to  and 
fro,  serves  to  renew  the  water  in  the  branchial  chamber  lying 
between  the  lateral  portions  of  the  carapace  and  the  body- 
walls.  On  account  of  this  action  this  appendage  is  usually 
spoken  of  as  the  scaphognathite.  The  three  anterior  thoracic 
appendages  are  maxillipeds,  the  third  one  frequently  becom- 
ing almost  limblike,  a  characteristic  which  distinguishes  the 
live  posterior  pairs  of  appendages  which  are  adapted  for  walk- 
ing and  are  hence  termed  the  pereiopods.  Tliey  lack  all 
traces  of  exopodites,  though  usually  bearing  epipodites  and 
branchiae,  and  a  certain  number  of  the  anterior  ones  are  fre- 
quently chelate,  thus  serving  for  the  prehension  of  food.  The 
number  of  the  pereiopods  has  suggested  the  name  given  to 
the  order.  The  abdominal  appendages  are  sometimes  want- 
ing or  very  rudimentary,  but  when  present  are  biramous  swim- 
ming-feet and  are  hence  termed  pleopods — a  term  equally 
applicable  in  some  other  groups. 

The  branchia'  lie  entirely  within  the  branchial  chamber 
and  are  developed  in  connection  with  the  thoracic  append- 
ages. They  may  be  seated  U})on  the  basal  joints  of  tlie  ap- 
pendages (podobranchia),  or  upon  the  joint  between  the  ap- 
pendage and  the  body-wall  (arthrobranchia),  or  finally  upon 
the  body-wall  itself  (pleurobranchia).  All  three  kinds  may 
occur  on  the  same  segment,  so  that  the  entire  number  of  gills 
may  be  much  grej'ier  than  that  of  the  appendages,  amount- 
ing in  the  Lobster  to  no  less  than  twenty  in  each  branchial 
chamber. 

The  heart  is  a  short  saclike  organ  lying  in  the  thorax  and 
possessing  as  a  rule  three  ]iairs  of  ostia,  one  pair  being  situ- 
ated on  the  dorsal  surface,  one  upon  the  sides,  and  the  third  t)n 


TYPE  CRUSTACEA. 


411 


the  veutral  surface.  Arteries  pass  off  from  both  ends  of  the 
heart.  Otocjsts  are  always  developed  iu  the  basal  joiuts  of 
the  autenuules. 

3.  Suborder  J/«(?n/ra. 
Iu  the  Macrura  the  abdomeu  ts  well  developed  aud  usu- 
ally as  loug  as  the   cephalothorax,  aud  is  provided  with  its 
full  complenieut  of  appendages,  the  sixth  pair  formiug  with 
the  telsou  a  tail-fiu.     Exceptious  to  these   arraugeuieuts  oc 
cur  ;  lu  the  Heriuit-crabs,  Eupagurus,  which  inhabit  the  empty 
.shells    of    Gasteropod    Mol- 
lusks,  the  abdomen  is  gener- 
ally soft  aud  uusymmetrical, 
since  it  is  coiled  around  the 
columella   of   the    shell,    but 
terminates  in  a  movable  tail- 
fin  which  serves,  together  with 
the  remaining   pleopods   and 
the  last  (and  sometimes  also 
the   penultimate)    pereiopod, 
wliich  is  bent  dorsally,  to  re- 
tain the  animal  in  the  shell. 
The    chehB   of    the    anterior 
pereiopods  are  generally  uu- 
0(]ual  in  size,   serving  to   oc- 
clude the  mouth  of  the  shell, 
and  occasionally  the  abdomi- 
Jial    a])pendiiges  of  only   one 
side   are    develo])ed.     In   the 
genus  llippa  too  the  abdomeu, 
though  Avith  a  well-develoi)ed 
Mild  calcified  cuticle,  it,  short, 
the  terminal  half  being   bent 

M|.     under    the    thorax,  the  F.o.  187.-J.  a  vorxo /.^r^yir  (n.i«p,e.i 

condition      characteristic  of  '''"•"  Hhooks);   n,  Eupayurus   biru 

the    Crabs    being     thus  n,,.  '""'/"""fn'r i-ki-nks). 
pioachod.      In  some  fo 


ap- 


t'.ef.mrth  andfiftl 


as    Sorqpstt's   and     T.uolfi 


er. 


aent,  but  more  usually  all    th 


1  peren)pods  may  be  rudimentarv 


or  even  ab- 


•on.. 


i^^S'" 


5 


eso  appendages  are  well  dovel- 


412 


IN  VERTEBRA  TE  MORPHOL  0  G  Y. 


oped,  the  anterior  ones  becoming  chelate.  Id  the  Crayfish, 
Carnbarus,  and  the  Lobster,  Homarus,  the  first  pereiopod  is  an 
exceedingly  strong  chela,  and  the  same  arrangement  is  found 
in  Alpheus,  while  in  the  Shrimp,  Pulcpmonetes,  the  second  pe- 
reiopod is  somewhat  longer  than  the  first. 

The  branchiie  are  usually  numerous  and  are  for  the  most 
part  bunches  of  cylindrical  processes,  but  in  Palo'inonetes  and 
the  jal-.'  "•^is  'xiid  prawns  in  general,  which  form  the  family  Ca- 
rididc  n  the  Hermit-crabs  they  are  lamellate.  In  Lucifer 

branclu;..  are  entir3ly  wanting.  The  Macrura  are  essentially 
marine,  a  few  forms,  such  as  Camharus  and  some  species  of 
Palwrnon,  occurring  in  fresh  water.  The  genus  Birgus,  one  of 
the  Hermit-crabs,  commonly  known  as  the  robber-crab,  is 
almost  entirely  terrestrial,  living  in  holes  in  the  ground  and 
climbing  cocoa-nut  palms  for  the  sake  of  the  nuts,  on  which 
it  lives.  In  harmony  with  its  terrestrial  life  the  inner  surhice 
of  the  branchial  chamber  is  thrown  into  folds  richly  supplied 
with  blood-lacunae,  a  lunglike  structure,  recalling  the  lungs  of 
the  Pulmonate  Gasteropods,  being  thus  developed. 

3.  Suborder  Bracliyura. 

In  the  Brachyura  the  body  is  exceedingly  compact,  the 
abdomen  being  very  much  reduced  in  size  and  usually  desti- 
tute of  a  tail-fin,  and  in  addition 
is  bent  up  so  as  to  lie  in  a  groove 
upon  the  ventral  surface  of  the 
cephalothorax.  In  some  casts 
the  cephalothorax  is  almost  glo- 
Ituhii',  though  prolonged  anterior- 
ly into  a  strong  rostral  spine,  as 
in  Ijhhi'm,  the  s})ider-crab  ;  -^yfliilo 
in  other  cases  it  is  more  fiatteiu'il 
and  triangular  in  shape  and  lacks 
a  distinct  rostrum,  as  in  lli' 
edible  crab,  CaUinectes,  the  hulv- 
crab,  Plaiyovychns,  and  the  com 
mon  crab,  Cancer,  ami  in  others  again  is  more  or  les- 
(juadninguhir  and  thicker,  as  in  /*i)inot/ieres.  the  ovHtpr-criih 
Ocypuda,  the  sand-crab,  and  Gdanimiui,  the  tiddler-crab.    Tlii 


Fio.    188.  —  Panopmis    deprcssus 
(afiiT  Embrton  from  Vkrral). 


TYPE  CRUSTACEA. 


413 


}  CrayfisL, 
opod  is  an 
t  is  foimd 
second  pe- 

r  the  most 
lonetes  aud 
family  Ca- 
in Lucifer 
essentially 
species  of 
jus,  one  of 
jr-cral),  is 
ound  aud 
,  on  wliicli 
ler  surface 
f  supplied 
e  luijgs  of 


mpact,  the 
:ally  desti- 
1  addition 
ii  a  groove 
.ce  of  tht» 
>me  cases 
liuost  gl<»- 
1  anterior- 
.  spine,  as 
•ab ;  •^vhilo 
3  tiatteiu'il 
aud  lacks 
,s  in  tin 
the  ladv- 
thc  com 
e  or  less 
kster-criili. 
)rab.    Til. 


antenuules  are  small  aud  they  and  the  eyes  can  be  partially 
concealed  in  a  groove  on  the  anterior  edge  of  the  carapace. 
The  abdominal  appendages,  with  the  exception  of  the  anterior 
cue  or  two  pairs  Avhich  are  adapted  for  copulation,  are  ab- 
sent  in  the  males,  while  the  females  generally  possess  four 
pairs,  to  which  the  ova  are  attached. 

The  gills  are  generally  few  in  number,  except  in  Porcel- 
hina  and  some  allied  forms,  and  are  usually  lamellate  in  form. 
While  essentially  marine  in  habit,  the  Brachyura  are  fre- 
(piently  more  or  less  terrestrial,  the  sand-crabs,  Ocypoda,  and 
the  fiddler-crabs,  Gelasimus,  living  in  holes  in  the  sand  just 
above  high-tide  mark,  while  the  land-crabs,  Gecarcinus,  of  the 
tropics  may  live  some  distance  from  the  sea,  migrating  to  it 
in  armies  during  the  breeding-season.  A  few  forms,  such  as 
the  genus  Telphusa,  are  aquatic. 

III.  Subclass  Arthrostraca. 

The  Arthrostraca,  with  the  exception  of  the  small  group 
of  the  Anisopoda,  are  destitute  of  a  carapace,  and  the  tho- 
racic appendages,  with  the  exception  of  the  first  pair,  are 
jointed  walkiug-limbs  lacking  an  exopodite.  The  anterior, 
or  in  some  cases  the  anterior  two  thoracic  segments  fuse 
with  the  head,  the  appendages  of  these  segments  differing 
from  those  of  the  free  segments,  being  modified  to  assist  in 
the  process  of  mastication,  whence  they  are  termed  maxilli- 
peds.  The  abdomen  is  ,  .nposed  of  six  segments  provided 
with  ai)pendages,  and  of  a  terminal  telson  ;  occasionally  the  va- 
rious segments  fuse  together,  and  in  some  forms  the  abdomen 
is  reduced  to  a  small  unsegmented  structure.  Platelike  ap- 
pendages  attached  to  the  basal  joints  of  some  of  the  thoracic 
limbs  form  by  their  meetii.g  and  overlapping  a  brood-pouch 
in  which  the  ova  undergo  their  development. 

The  lateral  compound  eyes  are  not,  except  in  Tanais,  sup- 
ported on  stalks,  a  characteristic  which  has  suggested  the 
tinin  EdriophfJmhnata  sometimes  applied  to  the  group. 

1.  Order  Anisopoda. 
Tlie  Anisoiiodn.,  are  evduuivfily  marine  forms  in  which  the 
two  anterior  thoracic  segments  are  fused  with  the  head  and 


is;: 

.Jyi».,J 


414 


IN  VERTEBRA  TE  MORPIIOLOO  Y. 


covered  in  at  the   sides  by  duplicatures  of  the  body-wall, 
M'hich  euclose  a  small  respiratory  cavity. 

The  anteimules  and  autemiio  are  iiuiramous  except  in 
ApFCMies  in  which  the  auteuimles  carry  two  terminal  'Hagella. 
The  palps  of  the  anterior  maxilhe  project  into  the  respiratory 
chamber  aud  serve  for  cleansing  it,  and  the  first  thoracic 
limbs,  the  maxillipeds,  bear  each  an  epipodial  branchial  ap- 
})eudage  lying  in  the  respiratory  chamber.  This  limb  aud 
the  succeeding  one  are  chelate,  the  inner  angle  of  the  penul- 
timate joint  being  prolonged  into  a  process  against  which  the 
terminal  joint  may  be  apposed.  The  abdominal  appendages 
are  biramous  swimming-feet  in  Tanais  aud  Apseudes,  the  last 
pair  being  in  Anthura  especially  enlarged  to  form  with  the 
telsou  a  terminal  finlike  structure. 

2.  Order  Isopoda. 

The  majority  of  the  Isopoda  are  marine,  the  genus  Asellns 
(Fig.  189),  however,  occurring  in  fresh  water,  while  Oniscm, 
ForceUio,  and  ArmadilUdium  are  terrestrial,  being  commonly 
known  as  Wood-lice  or  Sow-bugs.  The  body  in  all  forms  is 
more  or  less  flattened  dorso-veutrally  aud  only  the  anterior 
thoracic  segment  is  fused  with  the  head,  the  remaining  sevei' 
remaining  perfectly  distinct.  There  is  no  trace  in  the  aduJt 
of  a  carapace,  and  the  abdominal  segments  are  usually  small 
and  may  be  fused  more  or  less  completely. 

The  maxilhe  are  destitute  of  palps  and  the  maxillipeds 
{mxp)  usually  fuse  together  to  form  a  sort  of  lower  lip.  The 
remaining  thoracic  appendages  are  limblike  and  do  not  bear 
any  respiratory  appendages,  though  lamelhe  are  attached  to 
the  basal  joints  of  several  of  them  in  female  individuals, 
serving  to  form  a  brood-pouch.  The  five  posterior  abdominal 
appendages  are  biramous  aud  lamellar  {ah),  serving  both  for 
swimming  and  for  respiration,  the  anterior  pair  (op)  usually 
becoming  hard  and  forming  an  operculum  which  covers  in 
the  posterior  more  delicate  appendages  and  in  the  terrestrial 
forms  may  have  branching  sjjaces  containing  air  (trachea) 
ramifying  through  them. 

The  heart  (Id),  in  confornuty  to  tlif  position  of  the  respira- 
tory organs,  is  situated  print'i[)ally  in  the  abdomen,  exteudiui; 


bodj-wall, 

except  in 
lal  ^agella. 
.'espiratory 
it  thoracic 
iriichial  ap- 

limb  am] 
the  peuul- 

which  the 
ppeuda^es 
is,  the  hist 
a  with  the 


TTFE  CRUSTACEA. 


415 


le  Oniscu.s, 
comnioL»ly 
11  forms  is 
e  auterior 
liiig  sevei' 
I  the  atluJt 
lally  small 

laxillipetls 

lip.     The 

o  Lot  bear 

ttached  to 

uliviiluals, 

ibdomiiial 

^  both  for 

yp)  usually 

covers  in 

terrestrial 

(trachea' ) 

ie  res])ira- 
exteudiuu 


forwards  only  a  short  distance  into  the  thorax  segment.  It 
possesses  one  or  two  pairs  of  ostia  and  is  closed  behind, 
giving  off  in  front  anti  at  the  sides  numerous  aortse.  A  shell- 
gland  has  been  observed  in  some  Isopoda,  but  the  antennary 
gland  is  wanting. 

Although  the  majority  of  the  marine  forms,  such  as  Idotea 
and  Sphmroma,  lead  a  free  existence,  nevertheless  there  are 
certain  parasitic  forms.  Thus  the  genera  Cymothoa  and  jEga 
are  parasitic  on  the  skin  or  in  the  mouth  of  fishes,  but  also 
retain  the  power  of  swimming  and  consequently  are  not  much 

at'  e        vn  _  1  ]      hf 


Fia.  \^9.—Asellu8  communis,  Diagram  op  STnucruiiE. 

ab  =  abdominal  appendages.  l  =  liver-ciBcn. 

(10  =  aoila.  tnnp  =  maudibular  palp. 

«<•  =  antennule.  mxp  =  maxilliped. 

at-  =  auteiina.  r  =  rectum. 

ce  =  cerebral  ganglion.  «  =  stomucli. 

ch  =  chelate  limb.  t  =  tiioracic  appendage. 

ht  =  heart.  mi  =  veutial  uerve-coid. 

modified.  The  genus  Bopyrus,  which  lives  in  the  branchial 
cavity  of  shrimps,  becomes  in  the  female  some\\  hat  distorted 
in  shape  and  asymmetrical,  and  the  mouth-parts  become 
transformed  into  a  suctorial  proboscis  and  the  eyes  disap- 
pear. The  male,  however,  which  is  mucli  smaller  than  the 
female,  retains  the  eyes  and  does  not  depart  from  the  usual 
symmetrical  body  form.  The  degeneration  of  the  female 
proceeds  much  farther  in  the  genus  Entoniscus,  which  lives 
either  partly  or  wholly  included  within  the  body-cavity  of 
other  Crustacea  and  assumes  a  saclike  unsymmetrical  form, 
recalling  to  a  certain  extent  that  of  some  of  the  ])arasitic 
Copepoda.  At  tlse  time  of  pairing  both  sexes  are  alike  fully 
•segmented  and  with  an  almost  full  comi)lement  of  appendages. 


i— tail 


416 


INVERTEBRATE  MORPHOLOGT. 


After  copulation,  liowever,  the  female  assumes  the  degener- 
ated form,  while  the  male  dies. 


Sill 
^^ 

c 

t 

f! 

ill 


3.  Order  Amphipoda. 

Like  the  Isopoda  these  are  essentially  marine  forms, 
though  the  genus  Gammarus  is  aquatic  and  Orchestia 
(Fig.  190)  partly  terrestrial,  living  among  the  v.-rack  on  sea- 
beaches  just  beyond  the  reach  of  the  waves.     The  body  in 

ht 


Fig.  190.— Diagram  of  Stuuctuke  op  Orchestia  cavimana  (after Nebeski). 

aO  ~  nntennule.  m  =  uioutb. 

at^  =  auieuiia.  mt  -  Malpighian  tubule. 

br  —  brail  cilia.  oc  =  eye. 

ce  =  cerebral  ganglion.  r  =  rectum, 

ch  =  chf^laif!  limb.  rd  =  reprcductive  duct. 

7tt  =  heart.  ro  =  reproductive  organ. 

I  =  liver-cajca.  vn  =  ventral  nerve-cord. 

the  Amphipoda  is  laterally  flattenud  and  presents  therefore  a 
very  different  appearance  from  that  of  the  Isopoda,  though, 
as  in  that  group,  lacking  all  traces  of  a  carapace.  The  first 
thoracic  segment  is  fused  with  the  head,  and  in  Caprella  and 
Ci/nmus  the  second  segment  likewise.  The  appendages  of  the 
head  and  the  maxillipeds  resemble  those  of  the  Isopoda,  and 
the  remaining  thoracic  appendages  are  limblike,  a  certain 
number  of  the  anterior  ones  frequently  possessing  a  terminal 
joint  capable  of  flexion  upon  the  succeeding  one,  or  eveu 
being  chelate.  The  five  posterior  limbs  or  the  third  and 
fourth  only  beai  epipodial  lobes  which  serve  as  branchiae,  and 


le  degener- 


ine   forms, 
Orchestia 
,ck  on  sea- 
he  body  iu 


TYPE  CRUSTACEA. 


417 


ter  Nebeski). 
iibule. 

duct. 

organ. 

!-cord. 

;lierefore  a 
ia,  though, 

The  first 
iprella  and 
iges  of  the 
)poda,  auJ 

a  certain 
a  terminal 
3,  or  eveij 
third  aud 
iichifc,  and 


a  number  of  the  limbs  also  iu  females  bear  lamella)  which 
may  enclose  a  brood-pouch.  The  three  anterior  abdominal 
limbs  are  biramous  and  serve  for  swimming,  while  the  three 
posterior  ones,  also  biramous,  are  frequently  directed  back- 
wards and  serve  as  springing  organs,  the  springing  powers  of 
Orchestia  having  gained  for  it  the  mime  of  the  Beach-flea.  In 
Caprella,  which  crawls  about  over  colonies  of  Hydroids  and 
Polyzoa,  and  Cymmis,  which  is  parasitic  upon  the  skin  of 
whales,  the  abdomen  becomes  almost  rudimentary  and  is  des- 
titute of  appendages. 

The  heart  {U)  lies  in  the  thoracic  region  in  the  anterior 
five  or  six  segments  and  possesses  from  one  {Corophiuni)  to 
three  ostia.  It  is  prolonged  into  an  aorta  at  either  end.  In 
connection  with  the  mid-gut  portion  of  the  digestive  tract,  iu 
addition  to  the  four  so-called  liver-caeca  (l)  is  a  pair  of  gluud- 
ular  cfBca  which  seem  to  be  excretory  in  function  and  have 
been  termed  Malpigluan  tubules  {mt).  An  antennary  gland 
occurs,  but  the  shell-gland  is  apparently  unrepresented  in 
adults. 

Development  of  the  Crustacea.— The  majority  of  the  Crus- 
tacea pass  through  a  more  or  less  complicated  series  of 
metamorphoses,  the  larval  forms  being  highly  suggestive 
when  studied  from  the  phylogenetic  standpoint.  A  few  forms, 
especially  those  inhabiting  fresh  water,  abbreviate  their  de- 
velopment considerably,  so  that  the  young  animal  when  it 
leaves  the  egg  practically  may  diff'er  from  the  parent  only  in 
size {Cambarus),  and  among  the  higher  forms  the  development 
is  generally  abbreviated  to  the  extent  that  a  greater  or  less 
number  of  the  larval  stages,  characteristic  of  lower  forms,  are 
passed  through  while  the  young  animal  is  still  within  the  egg- 
membrane,  only  the  final  stages  being  free-swimming. 

Throughout  the  Entomostraca  the  first  larval  form  Avhicli 
li:.tclies  from  the  egg  is  termed  the  NaupUus  (Fig.  191)  and 
diliers  markedly  fr(,m  the  adult,  chiefiy,  however,  in  the  small 
number  of  appeiidagos  it  possesses.  The  body  in  typical 
iorms  shows  no  trace  of  segmentation  and  possesses  a  single 
median  eye  geuf^rally  \-shaped.  But  three  pairs  of  limbs 
Hie  present,  which  become  transformed  later  into  the  anten- 
imles,  antennie,  and  the  mandibles  of  the  adult.    The  NaupHar 


!!S 


s 

Si* 

■—•IS 


go 


«... 


418 


INVEliTEBliATE  MOltPIIOLOOT. 


i'( 


antennules  are  uuiramous  aud,  like  tlie  other  limbs,  but  indis- 
tinctly jointed,  the  antennso  and  mandibles  bein<,',  however, 
biramous  and  possessing  strong  setiB  at  their  bases  which 
function  as  jaws,  though  both  j^airs  of  appendages  are  essen- 
tially locomotor.  Judging  from  the  appendages,  therefore,  the 
Nauplius  may  be  regarded  as  consisting  of  live  segments,  one 
corresponding  to  the  prostoinial  lobe  of  Annelids  and  contain- 
ing the  primitive  cerebral  ganglion  (archicerebrum),  one  cor- 


FiG.  191.— Nauplius  op  Cetochihis  septentrionalis  (utter  Qhobbeh). 


responding  to  each  pair  of  appendages  and  one  to  the  region 
of  the  body  behind  the  mandibles. 

A  Nauplius  of  this  simple  form  may  be  regarded  as  typical 
and  is  that  which  is  found  in  the  majority  of  the  Copepoda  aud 
in  the  Cirrhipedia  as  well  as  in  some  Branchiopoda  {Edherhi, 
Limnodia).  In  the  Ostracoda  the  arrangement  of  the  limbs 
and  segments  is  the  same,  but  the  bivalved  shell  characteristic 
of  the  adult  is  already  developed,  giving  the  Nauplius  an  ap- 
pearance very  different  from  that  of  the  Copepoda.  Not  uu- 
frequently,  however,  as  for  instance  in  Apus  among  the 
Branchiopoda,  and  Leptodorn  among  the  Cladocera  (the  re- 
maining Cladocera,  so  far  as  is  known,  leave  the  egg  with  the 
adult  form),  the  Nauplius,  though  jiossessing  only  the  three 
.  pairs  of  appendages,  yet  shows  indications  in  the  post-maudih- 
ular  region  of  a  varying  number  of  additional  segments,  and 
to  this  form  it  is  convenient  to  apply  the  name  BletanaupUm. 
As  a  rule  in  the  Entomostraca  further  development  con- 
sists of  a  series  of  moults  (ecdyses),  an  increase  in  the  number 
of  segments  and  appendages  and  modifications  of  the  hitttu' 
taking  place  at  each  ecdysis,  until  the  adult  form  is  attained. 
No  special  larval  forms  beyond  the  Nauplius  are  common  to 


TYPE  CRUSTACEA. 


419 


bs,  but  iudis- 
11  J,',  however, 
bases  which 
es  are  esseii- 
herefore,  the 
jgmeuts,  one 
autl  coutain- 
im),  cue  cor- 


■  Qrobbkn). 

io  the  re<fiou 


sd  as  typical 
^pepoda  aud 
da  {Jfstheriit, 
3f  the  liin}).s 
haracteristic 
iplius  au  aj)- 
ia.     Not  uii- 

amoug  the 
3era  (the  re- 
egg  with  the 
ily  the  three 
)ost-maudil)- 
igmeuts,  and 
^Ietanauplii(K. 
:)pmeiit  con- 
i  the  liumlxr 
if  the  hitter 
1  is  attained. 

coimnon  to 


all  the  members  of  the  class,  aud  it  is  oulyin  the  Cirrhipedia 
that  a  second  definite  larval  form  can  be  distinguished,  the 
Cjpris-larva,  to  which  attention  has  already  been  called  (p.  399). 
lu  the  Malacostraca  the  occurrence  of  a  free-swimming 
Xauplius  is  the  exception  rather  than  the  rule,  and  indeed 
larval  forms  are  practically  wanting  in  some  groups,  such  as 
the  Leptostraca  and  Arthrostruca,  and  in  certain  species  or 
families  of  other  groups  (e.g.  3Tysid(e,  Camharus).  In  the 
genus  Penmis  among  the  Decapods,  and  in  Euphcmsia  among 
the  Schizopods,  a  typical  free-swimming  Nauplius  occurs,  and 
in  Lucifer  the  embryo  leaves  the  egg  in  the  form  of  the  Meta- 
nauplius.  In  the  majority  of  forms  these  stages  are  passed 
over  while  the  embryo  is  still  within  the  egg-shell,  aud  it 
hatches  only  when  it  has  acquired  a  greater  degree  of  develop- 
ment. In  such  forms  as  Renccm,  Ewphansia,  and  Lucifer  the 
Metauauplius  stages  pass  into  what  is  termed  the  Protozom 
(Fig.  192,  A)  a  stage  also  passed  over  within  the  egg  by  the 


mx> 


Fjg.  193.—^,  ProtozoMsa  op  Lucifer  (after  Brooks);   B,  Zoea  of  Palmmoneies 

(after  Faxon). 
At^  =  autenuule. 

AC  =  antenna.  7nx\ 

c  =  cerebral  ganglion.  mp^, 

E  =  compound  eye. 
h  =  heart. 

8  =  stomnch. 


m  =  mandible. 
7nx^  =  maxillae. 
mp'^  =  maxillipeds. 

oe  =  simple  eye. 

r  =  rostrum. 


majority  of  Malacostracaus,  though  occurring  as  the  first 
larval  stage  of  some  Stomatopods.  It  is  characterized  by  the 
development  of  two  maxilla)  aud  the  two  or  three   anterior 


i 

kS"* 
•■III, 


se 


420 


IN  VERTEBRA  TE  MORPHOL  00  Y. 


Ill 


thoracic  appendages  in  addition  to  those  already  present  in 
the  Nauplius,  and  furthermore  by  the  distinct  separation  of 
the  body  into  an  anterior  cephalo-thoracic  portion  covered  by 
B.  carapace   and  a  posterior  abdomen  which  is  usually  but 
imperfectly  segmented.     This  stage  is  succeeded  sometimes 
after  two  or  more  ecdyses  by  the  Zota  (Fig.  192,  B),  a  stage  in 
which  the  majority  of  Decapoda  leave  the  egg.     It  is  distin- 
guished from  the  Protozoea  principally  by  the  perfect  segmen- 
tation of  the  abdominal  region,  tli  ugh  it  still  possesses  no 
appendages,  unless  it  be  rudiments  of  the  sixth  pair,  and  it 
is  furthermore  characterized  by  the   compound   eyes   beiug 
stalked,  a  feature  but  slightly  indicated  in  the  Protozoea,  in 
which  stage  they  make  their  appearance.     The  Zoea  stage  in 
the  Brachyura  is  generally  characterized  by  the  development 
of  spines,  sometimes  of  enormous  length  {ForceUana),  ui)on  the 
dorsum  and  sides  of  the  carapace. 

In  such  a  form  as  Euphausia  the  next  stage  is  the  adult, 
but  in  the  Decapods  other  larval  stages  intervene  before  tlio 
adult  condition  is  reached.  The  first  of  these  is  characterized 
in  the  majority  of  the  Macrura  by  the  appearance  of  the  re- 
maining thoracic  appendages  which  were  unrepresented  in 
the  Zoea,  in  the  form  of  biramous  structures  closely  resem- 
bling the  thoracic  appendages  of  the  Schizopoda,  whence  tlie 
stage  ia  generally  termed    the  Mysis   stage  (Pig.  193).     Tlu; 


Via.  198.-Mvfiis8TAOE  ov  LonsTEH,  ITomarua  americanua  (afters.  I.  SMiin 


abdominal  appendages  also  develop  dining  this  stm^e. 
Among  the  Hermit-crabs  (Paguridie)  and  the  Brachyura  ihv, 
development  is  to  a  certain  extent  abbreviated,  the  pereiop.Mls 
never  being  represented  by  biraniouH  nppHMdjvt'es  but  biiun 
from  the  first  uniramous,  and  in  these  forms  therefore  a 
true  Mysis  stage  never  occurs.     To  the  correspoiidiu^r  Htagr, 


present  iu 
paratiou  of 
covered  by 
usually  but 

sometimes 
I,  a  stage  iu 
[t  is  distiu- 
!ct  segmeu- 
>ssesses  no 
pair,  aud  it 
3jes  being 
otozoea,  iu 
ea  stage  iu 
ivelopmeut 
),  upou  the 

the  adult, 
before  tlie 
iracterized 
of  the  re- 
5seuted  iu 
ely  reseui- 
.'heuce  the 
[93).     The 


TYPE  CltUSTACEA. 


ir  8.  I.  SMirn). 

lis  stage, 
lyura  the 
ereiopodrt 
[)ut  bciug 
lereforo  a 
\i\,:,  stage, 


421 


or  rather  to  one  in  which  the  pereiopods  are  indicated  but 
not  fully  developed,  the  term  Metazoea  is  applied.  Further- 
more in  certain  Ma  crura,  such  as  Scyllarus  and  Palinurus,  the 
Mysis  stage  is  represented  by  peculiarly-shaped  transparent 
larvse  which  have  been  termed  Phyllosoma,  or  glass-crabs. 
The  carapace  is  divided  into  two  portions,  of  which  the  an^ 
terior  or  larger  covers  iu  the  head  region  and  the  posterior 
the  thorax,  the  body  being  throughout  flat  aud  the  ab- 
domen very  small  The  pereiopods,  of  which  in  the  earliest 
stages  there  are  but  three,  are  biramous,  and  the  flrst  maxil. 


Fia.  104.-MEGALOPA-8TAOE  OF  Cancev  irroraius  (after  Emkrton  from  Vkrrill). 
hpeds  are  either  entirely  wanting  or  very  rudimentary.  Dur- 
ing successive  ecdyses  tlu>  missing  ai)peiulage8  are  gradually 
developed,  though  the  actual  trausformntiou  of  the  /^hijUoHoma 
into  the  youngest  Sci/llnrm  w  Palinnrm  stage  (whic'ii  is  de- 
ndedly  smaller  than  the  oldest  Phylhmma)  has\iotyet  been 


observed. 


The 


oni  the  MyRi.«  stagp  (n  tJio  adult 


;.,  ., n. 


a.s  a  rule 


chancre 

)  S| 

among  the  Macrura.     In  the  IJrachyura,  however, 


gradual,  and  no  special!}  definite  larval  forms  are  to  bo  found 


I 
IP 

I 


lift 


;.3H3 


"SI 


422 


INVEltTEBliA  TE  MORPUOLOG  Y. 


i 


the  Metazoea  becomes  trausformed  iuto  a  well-marked  form, 
the  Megalopci  (Fig.  194),  so  called  from  the  usually  largo  size' 
of  the  cephalothorax.  It  resembles  closely  a  Macruiau, 
diflfering  only  iu  the  abdomeu  being  relatively  small,  and 
becomes  converted  iuto  the  adiilt  form  by  the  doubling  of 
the  abdomeu  beneath  the  thorax.  A  Megalopa  stage  occurs 
also  in  the  Hermit-crabs,  but  is  not  so  well  marked  off 
from  the  young  fully-formed  auimals  as  iu  the  Brachyura. 

Affinities  of  the  Crustacea.— Tho  relationships  of  the  higher  groups  of 
the  Miilacostraca  to  one  another  are  clearly  siiown  by  their  larval  forms, 
the  Megalopa  showing  the  origin  of  the  Brachyura  from  Macruran  forms.' 
and  the  Mysis  stage  that  of  tlie  latter  from  Schi/.opod  ancestors.  When 
attempts  are  nuMle  to  go  still  further  difficulties  stand  iu  the  way.  As 
regards  the  Stomatopoda  it  is  to  be  noted  that  they  pass  through  a  stage, 
the  Erichthns,  in  which  the  thoracic  appendages  which  are  present  are 
biramous,  and  it  seems  probable  that  both  they  and  the  Cumacea  are  re- 
ferable back  to  Schizopod  ancestors.  The  Arthrostraca,  on  the  other  liaiid, 
are  probably  traceable  to  Cumacealike  ancestors,  while  the  Leptostraca 
represent  more  nearly  the  Entomostracan  ancestors  than  any  other  group, 
though  widely  diiferentiated  from  them  in  certain  particulars.  It  is  even 
still  more  difficult  to  trace  out  relationships  of  the  various  Entomostracan 
orders,  but  it  seems  fairly  clear  that  IMiyllopodan  forms  such  as  Aptis  are 
to  be  considered  as  representing  more  nearly  than  any  others  the  primitive 
Crustacea. 

As  regards  the  affinities  with  other  groups  verj'  interesting  questions 
arise,  two  possil)ilitics  seeming  to  be  open.  According  to  one  the  Crustacea 
have  been  derived  directly  from  segmented  Amu'lids,  through  forms  repre- 
sented in  a  modified  condition  to-day  by  Aptis.  The  lol)ed  iii)pen(lage  ol 
ApHs  is  a  modified  parapodium,  and  thesegnuMiiation  of  the  body  has  been 
inherited.  What  then  as  to  the  Nauplius?  According  to  this  view  it  has 
praeti('ally  no  ancestral  signiflcatice.  or  at  best  can  be  considered  only  as 
representing  a  Trocliophoro  larva  highly  modified  and  with  many  aiiiili 
characters  thrown  back  upon  it.  This  latter  idea  does  not  seem,  however, 
to  agree  with  tlu>  facts,  since  tlie  Trochopliore  is  an  unsegmented  structure 
and  can  be  eomparal)le  only  to  the  prostomial  and  first  aj)pendage-l)earin- 
segments  of  the  Nauplius.  In  other  words,  the  Nauplius  is  comparalih. 
if  comparai)l(^  at  all,  to  a  Trochopliore  p/ns  certain  additional  segnu'Uls. 
It  has  recently  been  suggested  that  po.ssibiy  the  Nauplius  may  represent 
nut  till'  Trochopliore  but  the  larval  Annelid  with  three  parapodia,  which,  as 
iiulieated  (p.  215),  is  a  well-marked  stage  in  the  development  of  maiiv 
Polyehnita.  Th(*  number  of  segmenta  is  jipparently  similar  in  the  Iwii 
forms,  and  the  idea  is  plausible.  If,  however,  iu  all  Cni.stacoa  a  gauiflio.K 
representing  a  segment,  intervene.-,  b.>t ween  the  archicerebral  ganglia  ami 
the  antennulary  (see  p.  iSTH),  then  the  Nauplius  has  potentially  one  80g 


me 

th( 
pr( 
wil 

a  s 

is  t 
the 
cat 
thii 


11. 


TYPE  CRUSTACEA. 


423 


rked  form, 
'^  larger  size 
Macruiau, 
small,  and 
oubling  of 
age  occurs 
narked  olt' 
shyura. 

ler  groups  of 
larval  forms, 
riiran  forms, 
itors.  WluMi 
he  way.  As 
lugh  a  stage, 

present  are 
aacea  are  r(!- 
)  other  liaiul, 

Leptostraca 
other  group, 
I.  It  is  ovt'ii 
itoinostracaii 
as  Apus  arc 
the  primitive 

ng  questions 
he  Crustacea 
forms  ropre- 
l)pen(iage  of 
ody  has  l)eeii 
J  view  it  lias 
ored  only  its 

many  adult 
m,  however, 
ied  siruetiiie 
lage-lM'ariiii,' 
comparalile. 
id  segments, 
ay  represent 
in,  which,  m 
nt  of  many 

in  the  two 
I  H  ifanifliuiii 
ganglia  and 
lly  one  su^: 


ment  more  than  the  Annelid  larva  and  the  comparison  will  not  hold  If 
the  direct  Annelid  origin  is  to  be  accepted,  it  seems  most  satisfactory  at 
present  to  regard  the  Nauplius  as  a  secondarily  acquired  larval  stage 
without  any  ancestral  significance. 

Another  suggestion  has,  however,  been  made  which  gives  the  Nauplius 
a  significance  and  traces  the  Crustacea  back  to  unsegmented  ancestors  It 
IS  to  the  effect  that  the  Nauplius  can  be  referred  to  Rotiferliko  ancestors 
the  remarkable  Hexarthra  with  its  six  processes  being  supposed  to  indil 
eate  the  line  of  descent.  It  is  exceedingly  doubtful,  however,  whether 
this  similarity  can  be  regarded  as  anything  more  than  a  superficial  one 


TYPE   CRUSTACEA. 


I. 


Class  ENTOMOSTUACA.-Number  of  segments  varies  ;  abdomen  without 
appendages  ;  larva  a  Nauplius. 

1.  Order  Phyllopoda. -Nambev  of  segments  variable ;  appendages 
with  branchiae. 

1.  Suborder  Bmnchiopoda. -Body  plainly  segmented  and  seg- 
ments of  thorax  more  numerous  than  six.  Apm,  Branchipus, 
Esthena,  Limnadia,  Limnetis. 

2.  Suborder  Cladomra.— Body  indistinctly  segmented  ;  with  bi- 
valved  shell ;    four  to  six  thoracic  appendages.      Daphnia 
Moma,  Sida,  Emdne,  Polypheimis.  ' 

a.  Order  Ostracoda. -W\t\i  bivalved  shell ;   body  indistinctly  seg- 
mented ;  two  thoracic  appendages.    Cypris,  Cythere,  Cypri- 
dina,  Halocypris. 
8.  Order  Vopepoda.-WMhont  shell ;  five  pairs  of  thoracic  limbs ; 
many  forms  parasitic  and  degenerate. 
1.  Suborder  EHcopepoda.-Tw^i  thoracic  segment  only  fused  with 
head ;  abdomen  cylindrical  and  segmented  except  in  higlily 
degenerated  forms.     Cyclops,   Cai,ff,omii,ptu,s,   HarparticMs 
Cafanm,  Cetochilns  (free-swimming)  ;  Notodelphi/s  (commen- 
sal istie)  ;  Corycuiui,  Happ/ifrina,  ErnasiluH,  Calfym,  Panda- 
rus  (piirtly  parasitic)  ;   Philichthys,  Penella,  I^rima,  Chon- 
dracaiithiis,  Achtheres,  AiichnreUa  (parasitic). 
3.  Suborder  liranrhiara.—AW  tlioracic  segmcnits  fused  with  head  • 
abdomen  small  and  lamellar,  partly  parasitic.     Arynlus. 
4.  Order ^CV;T///>f.r/,V,._s,.ssiIo  or  parasitic;    segmentation   indis- 
tinct; SIX  pairs  of  thoracio  appendages;  pass  through  Cypri.s 
stage.    Lepa.s,  Scalpellxm,  J Ua,  Jia/anm  (m^mile) ;  Ak'ippe, 
Cryptophialus    (boring)  ;     Proteolepas,    HaocuUna,    Ixiura, 
Ihndroyaster  (i»arasitic). 
11.  Class  MALAC()8TUACA.-Numl,er  of  se^  ...it«  constant ;  thoracio  seg- 
monts  eight,  abtiominai  seven  or  eigiu. 
1.  Subclass  hptostranu     With  l)ivalv(>d  shell ;  abdomen  with  eight 
segments.     NebuUa. 


I 


irl 


Sii 

I? 

!!! 
111 


424  INTEliTEBliATE  MOliPUOLOOT. 

2.  Subclass  Thoracostmca.—\S\t\\  carapace  covering  the  whole  or  a 
part  of  the  thorax  ;  abdominal  segments  seven. 

1.  Order /St7a>o/»orf«.— Thorax  completely  covered  ;  thoracic  append 

ages  biramous.    Mysis,  Eaphatinia,  SirieUa. 

2.  Order  Cwmacea.— Last  four  or  five  tiioracic  segments  not  covered 

by  the  carapace  ;   eyes  sessile    or    rudimentary.     Diastylis, 

Campylaspis. 
8.  Order  Stomatopoda.— Last  three  or  four  thoracic  segments  not 

covered    by    the    carapace;    eyes   stalked;    five  maxillipeds. 

Squilla,  Lysiosquilla,  Gonodactylus. 
4.  Order  Decapoda.  —  Thorax  completely  covered ;   five  posterior 

appendages    uuiramous  and  three  maxillipeds  ;    otocysts  in 

antennules. 
1.  Suborder  ifocrara.— Abdomen  usually  well  developed.     8er- 

gestes,   Lucifer,  Fenoetis,   PaJdmonetes,   Alplieus,  Cambarus, 

Homarus,  Eupayurus,  Binjiis,  Hippa. 
3.  Suborder  ifmc/i^ttm.— Abdomen  small  and  concealed  beneatli 

cephalothorax  more  or  less  i)erfectly.     I'brcellana,   Libinia, 

CalHitectes,    Platyonychus,    Cancer,    Pinnotheres,    Oci/poda, 

Gelasi)nus,  Gtcarcinns. 
8.  Subclass  ArtJirostraca.—No  shell  or  carapace  as  a  rule  ;  with  seven 

(or  six)  walking-limbs;  eyes  sessile. 

1.  Order  ^ /J /.so;w(/a,— Carapace  slightly  developed  :  first  two  tho- 

racic segments  fused  with  head  ;  branchii«  on  anterior  maxillu". 
A  seiiJes,  Tanais,  Anthnra. 

2.  Order  Tivo^wf^a.— No  carapace  ;  first  thoracic  segment  fused  wilh 

head  ;  body  flattened  dorso-vcJitrally ;  braneliitu  on  abdomi- 
nal appejidages.  A.selliis,  Onisen.s\  Porcellio,  Armndillid- 
ium,  Idotea,  Sphmoma  (free) ;  Cymothoa,  JEga,  Bopyriis, 
EntnniscuH  (parasitic). 
8.  Order  Amphipoda.—^o  carapace,  first  thoracic  segment  fused 
with  head  ;  body  flattened  laterally  ;  branchim  on  thoracic 
appendages.  Gammarus,  Vrr/ie.sfia,  Corophium,  Cyainns, 
Caprella. 

LITERATURE. 

GENKHAIi, 

H.  Milne-Edwards.     IlMoire  Natiirelle  des  Crustacea.    Paris,  1884-1840. 

r.  Mttller.     Fiir  Darwin.     Leipzig,  1804. 

H,  Oerataeoker.     Arihropodn.     nronn'-H  Klnsson   und  Ordnuiigeu  des  Tliici- 

reichs,  Btl.  v.  Ahtii.  1.     18(i(!-  (not  \ot  completed). 
C.  Claui.     UnterHii  chilli  gen  zur  Krforschung  der  genealogisehen  Orundlage  ikx 

Crmtnceen-St/nteviH.     Wien,  187ft. 
0.  Orobben.     7)w  Aiitennendri'me  der  Vrusfaceen.     Arboiten  ji.  d.  Zoolog.  Inst. 

Wieu,  111,  1881). 


ie  whole  or  a 

Dracic  append 

ts  not  covered 
y.     DiastyUs, 

segments  not 
)  maxillipeds. 

five  posterior 
;    otocysts  in 

.'doped.  Ser- 
!s,  Cambarm, 

oaled  beneatli 
tna,  Libinia, 
'es,    Ocypoda, 

0 ;  with  seven 

first  two  tlio- 
erior  maxilla". 

!nt  fused  with 

3  on  abdonii- 

Armndillid- 

'ga,  Bopi/riis, 

Bgment  fus(>(l 
)  on  thoracic 
sm,    Cyamits, 


TYPE  CRUSTACEA. 


423 


J4-1840. 
m  dus  Tliici- 
Orundliige  dfs 
Zoolog,  Inst 


J.  E.  y.  Boas     Studusn  iiber  die  Verwandtschaftsbeziehungen  der  Malakostraken 
Morpbolog.  Jahrbucb,  viir,  1883. 

J.  Cwriere      m  Selm-gane  dsr   Thieve,  mrgleichend-anatomisc?i  dargestellt 

Munich  and  Leipzig,  1885. 
C.   ClauB.    Ntue  Beitrdge  zur  Morphologie  der   Grustaceen.     Arbeiten  a    d 

Zoolog.  Inst.  Wien,  VI,  1886.  "      ' 

S.  Watase.     On  the  Morphology  of  lU  Compound  Eyes  of  Arthropoda.    Studies 

from  the  Biolog.  Laboratory.  Johns  Hopkins  Univ.,  iv.  1890 
G.  H   Parker.     The   Compound  Eyes  in   Crustaceans.    Bulletin  Museum  of 

Coiup.  Zoology,  XXI,  1891. 
C.  Grobben.     Zur  Kenntniss  des  Stambaumes  und  des  Systems  d^r  Grustaceen 

Sitzuugsber.  Akad.  wissenscb.  VVieii,  ci,  1893. 

PHYLLOPODA. 

A.  S_  Packard.     A    Monograph   of  North    American   Phyllopod    Crustacea. 

Twelfth  Annual  Report  U.  S.  Geolog.  Survey.     Washington.  1883 
C.  L.  Hernok.     A  Final  lieport  on  the  Crustacea  of  Minnesota.     Twelfth  An- 

uual  Report  of  the  Geolog.  and  Natural  History  Survey  of  Minnesota 

Minneapolis,  1884. 
C.  Claus.    Zur  Kenntniss  des  Bams  und  der  Entwieklung  von  Branchipus  staa 

nalts  und  Apus  cancriformis.    Abhandl.  k.  Akad.  wissenscb   Gottiutren 

xviir,  1878.  v^uiuufeen, 

A.  Weismann.     Ueber  Ban  und  Lebenserseheinungen  von  Leptodora  hvalina 

Zeitscbr.  fUr  wissenscb.  Zoologie,  xxrv,  1874. 
Beitrnge  zur  Naturgeschiehte  der  B^iphnoiden.     Zeitscbr.  fUr  wissenscb 

Zoologie,  xxvii-xxxiii.  1876-1879. 
E.  Ray  Lankester.     Observations  and  Reflections  on  the  Appendages  and  on  tU 

Nervous  System    of  Apus  cancriformis.      Quarterly  Jouru.   Microscon 

Science,  xxr,  1881.  '^' 

C.    Claus.      Untersuchungen   iiber   die    Organisation    und   Enttcicklunq   von 

Branchipus  und  Artemia.     Arbeiten  a.  d.  Zoolog.  Inst.  Wieu   vi   1886 
P.  Pelseneer.     Observations  on  the  Nervous  System  of  Apus.    Quarter!  v  Jouin 

of  Microscop.  Science,  xxv,  1885. 
P.  Samasia.     Untersuchungen  iiber  das  centrale  Nervensystem  der  Grustaceen 

Archiv  fllr  mikr.  Aiiat.,  xxxviir,  1891. 
G.  M.  Bernard.     The  Apodidm,  a  Morphological  Study.     London,  1892 
C.  Grobben.     Uie  Entwicklungsgeschichte  der  Moina  rectirostris,' etc     Arbeiten 

a.  d.  Zool.  Inst.  Wien,  ii,  1879. 

OSTHACODA. 

G.  E    Brady.    A  Monograph  of  the  Reeem  British  Ostraeoda.    Transactions 
Linnaean  Soc.  London,  yttt. 

C.  Clang.     Ueber  die  Organisaiion  der  ^^pridinen.     Zeitscbr.  far  wissenscb 
Zoologie,  TV,  1865 

Beitrdge  zur  Kenntniss   ier  siUauxmet  Ostracoden.     Arbeiten  a   d 

zoolog.  Inst.  Wieo.  xii,  18«8. 

G  W.  Muiler,   ihtracoden.  Fauna  und  Flora  des  Golfes  von  Neapfl.  Monoirr 
XXI.  1H»4. 


% 

>: 
111 

MM.. 

— .,» 

""""'^llBij- 


426 


IN  VERTEBRA  TE  MORPHOLOO  Y. 


Sii 

% 

lie 

»■« 


COPEPODA. 

C.  L.  Herriok.  A  Final  Report  on  the  Crustacea  of  Minnesota,  Twelfth  An- 
nual Report  of  the  Geol.  and  Nat.  Hist.  Survey  of  Minnesota.  Min- 
neapolis, 1884. 

W.  Giesbrecht.  Pelagische  Copepoden.  Fauna  und  Flora  des  Golfes  von 
Neapel.    Monogr.,  xix,  1893. 

C.  Glaus.  Ueber  die  Entwicklung,  Organisation  und  systematische  Stellung  der 
Arguliden.    Zeitschr.  fllr  wisseusch.  Zoologie,  xxv,  1875. 

C.  Holder.  Die  Qattung  Lernanthropus.  Arbeiten  a.  d.  zoolog.  Inst.  Wieu, 
II,  1879. 

M.  Hartog.  2he  Morphology  of  Cyclops  and  the  Relations  of  tJie  Copepoda. 
Trans.  Linnseau  Soc.  London,  2d  Series,  v,  1888. 

F.  Leydig.     Ueber  Argulus  foliaceus.    Archiv.  fUr  mikr.  Anat.,  xxxiii,  1889. 
C.  Grobben.     Die  Entwicklungsgescfiichte  von  CetocMlus  septentrionalis,  Qoodsir. 

Arbeiten  a.  d.  zoolog.  Inst.  Wien,  in,  1881. 

CIUUHIPEDIA. 

C.  Darwin.     A  Monograph  of  the  Subclass  Cirrhipedia.    London,  1851-1854. 
H.  de  Luoaze-Duthiers,     Ilistoire  de  In  Laura  Oerardim.     Archives  de  Zool. 

exper.  et.  gen.,  viii,  1880. 
P.  P.  C.  Hoek.     Report  ok  the  Cirrhipedia.     Scientific  Results  of  Voyage  of 

H.M.S.  Challenger.     Zool.,  viii,  1883;  x,  1884. 
Yves  DelBge.     Evolution  de  la  Sacculine.    Archives  de  Zool.  exper,  et.  geu., 

2ine  ser.,  11,  1884. 

LEPTOSTKACA. 

C.  Claus.  Ueber  den  Organismus  der  Nebaliiden,  und  die  systeriatischen 
Stellung  der  Leptostraken,     Arbeiten  a.  d.  Zool.  Inst.  Wieu,  viii,  1888. 

BCIIIZOPODA. 

G.  0.  SaiB.     Report  on  the  Schieopoda.     Scientific  Results  of  the  Voyage  of 

H.M.S.  Challenger,    xiii.  1885. 


CUMACEA. 


A.  Dohrn.     Ueber  Ban  und  Entwicklung  der  Cumaeeen,    Jenaische  Zeitschr. 

filr  Naturwiss  ,  v,  1870. 
G.  0.  Sara.     Report  on  the  Cuniacea.     Scientific  Results  of  the  Voyage  of 

H.M.S.  Challenger,     xix,  1887. 


8Tt)MATOPODA. 


C.  Claus.     Die  Kreislaufsorgane  und  Blutbewegung  der  Stomatopoden.    Arbeiton 

a.  d.  Zoolog.  Inst.  Wieu,  v,  1883. 
W.  K.  Brooks.     Report  on  the  Stomatopoda,     Scienliflc  Results  of  the  Voyage 

of  H.M.S   Challenger,     xvi,  1886. 


DECAPOUA. 


S.  I.  Smith.     Vnrioas  Papers  in  Trnns.  Connecticut  Academy  and  in  Reports 
of  the  U  S.  Commissioner  of  Fish  and  Fisheries. 


Twelfth  An- 
uesota.    Min- 

s  Golfes  von 

5  Btellung  der 

J.  Inst.  Wleii, 

tJie  Copepoda. 

XXXIII,  1889. 
nalis,  Qoodsir. 

1851-1854. 
lives  de  Zoo). 

)f  Voyage  of 

;per.  et.  geu., 


iysteriatisclien 
VIII,  1888. 


lie  Voyage  of 

3che  Zeitsclir. 
le  Voyage  of 

len.    Arbeitoi) 
)f  the  Voyage 

id  in  Reports 


TYPE  CRUSTACEA. 


427 


V.   Hensen.      Studien   uber  das   OehOrorgan   der  Decapoden.     Zeitscbr    ftlr 

wissenscb.  Zool.,  xiii,  1863. 
C.   Grobben.    Beitrdge  zur  Kenrdnm  der   mdnnlichen   OmJdechUorgane  der 

JJecapoden.  Arbeiten  a.  d.  Zoolog.  Inst.  Wieu,  i,  1878. 
T.  H.  Huxley.  TJie  Crayfish.  Loudon  and  New  York,  1881 
W.  K.  Brooks.    Lucifer:  a  Study  in  Morphology.     Philosoph.  Trans.  Royal 

boo.  London,  clxxiii,  1882. 
H.  Keichenbach.     Biudien,  zur  Entwicklungsgeschichte  des  Flusskreoses.     Ab- 

bandl.  Senckeuburg.  Gesellsob.  Frankfurt,  xiv.,  1886. 
W.   F    E.   Weldon.     Ccelom  and   Nephruiia  of  Palcemon  serratus.    Journal 

Marine  Biolog.  Assoc,  i,  1889. 
G.  H^   Parker      The  Hutology  and  Development  of  tJie  Eye  in  the  Lobster 

Bulletin  Museum  Comp.  Zoolog.,  xx,  1890. 
P.  Marchal.    Recherches  anaiomiques  et  physiologiques  sur  Vappareil  excreteur 

des  Crustaces  decapodes.    Archives  de  Zool.  exper.  et  gen.,  2me  ser.,  x, 

W.  Z  Brooks  and  F.  H.  Herrick.     The  Emh-yology  and  Metamorphosis  of  the 

Macroura.    Proc.  U.  S.  National  Acad.,  v,  1892. 
E.  J.  Allen.    Nephridia  and  Body-cavity  of  some  Decapod  Crustacea.    Quarterly 

Journ.  Microscop.  Science,  xxxiv,  1893.  * 

ARTBR08TRACA. 

0.  Harger.    Report  on  the  Marine  Isopoda  of  New  England  and  Adjacent 
WaUrs.    Report  of  the  U.  S.  Commisslouer  of  Fish  and  Fisheries  for 

18<8. 

A.  Delle  Valle.     Oammarini  del  Oolfo  diNapoli.    Fauna  und  Flora  des  Golfes 

von  Neapel.    Monogr.,  xx,  1893. 
P.  Mayer.     Caprelliden.    Fauna  und  Flora  des  Golfes  von  Neapel     Monoffr 

VI  and  XVI,  1882,  1890.  ^  '' 

0.  Nebeski.    Beitrdge  zur  Kenntniss  der  Amphipoden  der  Adria.    Arbeiten  a 

d.  Zoolog.  Inst.  Wien,  iii,  1890. 
E.  Kossmann.     Studien  uber  Bopyriden.    Zeitscbr.  fUr  wissenscb.  Zoologie 

XXXV,  1881  ;  Mitth.  a.  d.  Zoolog.  Station  zu  Neapel,  iir  1882  ' 

Yves  Delage      Contribution  d  felude  de  I'appareil  circulatoire  des  Crustaces 

ednophthalmes  marins.    Archives  de  zool.  exper.  et  gen.,  ix,  1881. 

APPENDIX  TO  THE  TYPE  CRUSTACEA. 

Order  Xiphosura. 

The  Xiphosura  is  a  group  which  possesses  many  Crus- 
tPceau  peculiarities,  and  also  many  foreign  to  that  group  and 
more  especially  characteristic  of  the  Arachnida ;  consequently 
It  IS  advisable  to  consider  it  as  an  order  by  itself,  intermediate 
between  the  two  types. 

A  single  genu?,,  Lhmdns  (Fig.  195),  with  few  species  consti- 
tutes  the  order,  the  members  of  which  are  popularly  known 


=^: 


I 


428 


INVERTEBRATE  MORPHOLOGY. 


as  King-crabs  or  Horseshoe-crabs.  They  are  large  forms 
measuring  a  foot  or  so  in  diameter,  and  the  body  is  composed 
of  three  portions.     The  anterior  is  a  broad  semicircular  ceph- 


PiG.  19fi.—Limulu8  Polyphemus,  Female,  from  the  Ventral  Surface. 
ab  =  abdomen  cp  =  cepbalothorax, 

an  =  uiiiis.  ol  =  olfactory  organ. 

ch  =  chelicera.  op  =  operculum. 

chi  =  chilnrium.  ap  =  spine. 

alothorax  (cp),  prolonged  backwards  into  sharp  points  at  its 
posterior  angles  and  bearing  upon  its  dorsal  surface  a  pair  oi 
compuuud  eyes  towards  the  sides  and  x  ear  the  median  line 
two  simple   eyes.     The  middle  region  is  the  abdomen  (ah). 


TYPE  CRUSTACEA. 


429 


arge  forms 
s  composed 
cular  cepli- 


L  Surface. 


ft 

an. 


oiuts  at  its 
36  a  pair  ol 
aediau  lino 
lomen  {ali). 


showing  but  faint  indication  of  segmentation,  and  bearing  on 
its  terminal  segment  the  anus,  behind  which  is  a  long  mova- 
ble spine  {sp),  the  post-abdomen,  forming  the  third  region 
and  to  be  regarded  probably  as  a  movable  prolongation  of 
the  dorsum  of  the  last  abdominal  segment. 

The  cephalothorax  bears  seven  pairs  of  appendages.  The 
first  pair,  the  chelicerce  (Fig.  195,  ch),  which  lie  in  front  of  the 
mouth,  are  small  and,  liiio  the  following  four  pairs,  are  chelate. 
These  together  with  the  sixth  are  much  longer  and  surround 
the  mouth,  their  basal  joints  being  provided  with  strong  bris- 
tles and  serving  as  jaws.  The  sixth  pair  of  appendages  differ 
from  their  predecessors  in  not  being  chelate  and  in  possessing 
upon  their  basal  joints  a  peculiar  process  which  has  been 
termed  the  flabellum  and  by  some  is  regarded  as  representing 
an  exopodite.  The  seventh  pair  of  appendages  is  very  differ- 
ent from  the  others,  forming  a  broad  fiat  plate,  the  two 
appendages  of  the  opposite  sides  meeting  in  the  middle  line. 
This  plate  covers  in  the  abdominal  appendages  to  a  certain 
extent  and  hence  is  termed  the  operculum  {op).  The  abdom- 
inal appendages,  o*  which  there  are  five  pairs,  resemble  the 
operculum  in  form,  and  like  it  allow  an  external  larger  exopo- 
dite and  an  inner  smaller  endopodite  to  be  distinguished. 
They  carry  upon  their  posterior  surfaces  series  of  large  leaf- 
like, thin-walled  folds  which  function  as  brauchif©. 

The  heart  (Fig.  196,  ht)  is  an  elongated  tubular  organ  lying 
in  the  posterior  part  of  the  cephalothorax  and  the  anterior 
part  of  the  abdomen,  and  possesses  eight  ostia.  Arteries 
arise  from  it  which  carry  the  blood  to  various  parts  of  the 
body,  eventually,  however,  opening  into  the  general  lacunar 
system.  The  blood  has  a  distinct  bluish  color  which  deepens 
on  exposure  to  the  air  and  is  due  to  a  copper-containing 
respiratory  pigment,  hiumocyanin. 

The  body  is  enclosed  in  a  hard  chitinous  cuticle,  and  in 
addition  a  peculiar  fibro-cartilaginous  plate,  the  endosternite, 
is  found  in  the  cephak)thorax  between  the  intestine  and  the 
nervous  system.  It  is  formed  by  the  fusion  of  a  number  of 
tendons  and  may  be  regarded  as  an  endoskeleton. 

The  mouth  is  an  elongated  opening  lying  between  the 
bases   of  the   anterior   cephalothoracic    appendages   and   is 


■^ 


430 


INVERTEBRATE  MORPHOLOGY. 


§i 


bounded  behind  by  a  pair  of  processes  which  rejiresent  a 
lower  lip  and  are  known  as  the  chUaria  (Fig.  195,  chi).  Tlie 
oesophagus  passes  upwards  and  forwards  and  dilates  into  a 
large  proventriculus  (Fig.  196,  pr)  in  the  front  part  of  the 
cephalothoracic  rhield,  and  this,  bending  upon  itself  and 
constricting  again,  opens  into  the  stomach  (s),  from  which  the 
intestine  {%)  passes  straight  back  to  open  on  the  ventral  sui*- 
face  of  the  body  at  the  base  of  the  terminal  spine.  The  inner 
wall  of  the  hind-gut,  oesophagus,  and  proventriculus  is  lined 
by  chitin,  which  in  the  last-named  structure  is  thrown  into 

^•^        ht 


vn 


Fig.  196.— Longitudinal  Section  through  a  young  Limulus  polyphemus, 

Diagrammatic  (after  Packard). 
ce  =  cerebral  gnuglion.  I  =  liver. 

es  =  eiidosternite.  pr  =  proventriculus. 

ht  =  Lean,  s  =  stomach. 

i  =  iutestiue.  vn  =  ventral  uerv<;-oord. 

folds  and  recalls  the  masticatory  apparatus  in  the  stomach 
of  the  Decapodous  Crustacea.  Into  the  stomach  there  open 
the  ducts  of  two  pairs  of  voluminous  digestive  glands  (I) 
which  occupy  the  greater  portion  of  tlie  cephalothorax  and 
are  much  branched  greenish  structures. 

The  nervous  system  consists  of  a  syncerebrum  (ce)  com- 
])osed  apparently  of  three  pairs  of  ganglia.  It  lies  in  front  of 
the  oesophagus,  sending  branches  to  the  compound  and  simi)Ie 
eyes.  Behind  the  oesopliagus  and  united  with  the  syncere- 
brum by  circumoesophageal  connectives  comes  a  series  of 
seven  pairs  of  ganglia  closely  approximated,  the  first  pair 
innervating  the  chelicerre  and  the  remaining  six  the  other 
thoracic  limbs  in  succession.  A  chain  of  six  pairs  of  ganglia 
lying  in  the  abdomen  is  connected  with  the  cephalothoracic 
series  and  innervate  the  abdominal  appendages. 


enresent  a 

chi).     Tlie 

ates  iuto  a 

art  of   the 

itself   and 

which  the 

entral  sui*- 

The  inner 

IS  is  lined 

irowu  into 


TYPE  CRUSTACEA. 


431 


i  polyphemus, 


IS. 


i-oord. 

6  stomach 
there  ojjeu 
glands  (/) 
horax  and 

I  (ce)  com- 

iu  front  of 

-nd  simple 

e  syncere- 

series  of 

first  pair 

the  other 

of  ganglia 

lothoracic 


As  already  noticed,  a  pair  of  simple  eyes  are  borne  upon  the 
dorsal  surface  of  the  carapace,  one  on  each  side  of  the  median 
line,  while  a  pair  of  larger  compound  eyes  are  situated  lat- 
erally.  The  structure  of  these  compound  eyes  is  peculiar 
(Fig.  197).  Over  their  surface  the  cuticle  is  considerably 
thickened  and  shows  upon  the  outer  surface  no  indication  of 
corneal  facets,  but  its  inner  surface  is  prolonged  into  a  num- 
ber of  papillae  (])  each  one  of  which  projects  iuto  a  depression 
of  the  ectoderm.     At  the  bottom  of  each  depression  is  a  bulb- 


FiG.  197.— Compound  Eye  op  Limulm  polyphemus,  Two  Ommatidia  (after 

Watase). 

c  =  central  cell.  ms  =  mesoderm. 

i  =  leas.  opn  =  optic  uerve. 

rt  =  retliiula, 

like  structure  composed  of  a  number  of  cells  arranged  in  a 
circle  and  constituting  a  retinula  (rt),  the  lower  ends  of  the 
cells  being  continued  inwards  to  form  part  of  the  optic  nerves 
{opn).  Upon  the  face  which  is  turned  towards  its  fellow  eacli 
retinular  cell  secretes  a  layer  of  chitiu,  and  these  various  chit- 
inous  rods  being  in  contact  there  is  formed  a  structure  com 
parable  to  the  rhabdom  of  the  Crustacean  eye.  In  the  centre 
of  the  retinular  cells  and  below  the  rhabdom  is  a  .single  clear 
cell  [c)  whose  lower  end  is  also  prolonged  into  a  nerve-fibre. 
Each  depression  with  its  retinula  and  the  chitinous  pjtpilla 
wniCti  tit."  lUtO  lu  and  represents  its  cornea  is  an  winmatidiiim 
and  the   development   shows   that  the  ommatidia  arise   as 


I 


432 


INTERTEBRATE  MORPHOLOGY. 


number  of  separate  invaginntions  of  the  ectoderm,  the  sides 
of  the  retinular  cells  which  secrete  the  rhabdom  being  iu 
reality  those  sides  which  before  invagination  were  at  tbe 
surface  of  the  body,  and  the  xhabdom  may  therefore  be 
regarded  as  composed  of  portions  of  the  general  cuticle  which 
have  been  separated  by  the  invagination. 

On  the  under  surface  of  the  carapace  in  the  median  line 
in  front  of  the  chelicerre  is  a  small  tubercle  (Fig.  195,  ol) 
which  contains  an  organ  supposed  to  be  olfactory  in  function, 
and  probably  some  of  the  setse  upon  the  basal  joints  of  the 
limbs  may  also  possess  a  similar  function. 

Nephridia  are  represented  by  a  single  pair  of  large 
reddish  bodies  lying  at  the  sides  of  the  cephalothorax.  Each 
gland  communicates  with  the  exterior  at  the  apex  of  a  papilla 
situated  on  the  interarticular  membrane  of  the  basal  joint  of 
the  fifth  thoracic  appendage,  and  is  at  first  a  tubular  organ 
and  nephridiumlike,  later  becoming  a  lobate  and  complex 
structure.  Chemical  analysis  indicates  an  excretory  function 
for  these  glands,  which  have  been  termed  the  "  brick-red  " 
glands  and  also  the  coxal  glands,  the  latter  term  indicating 
the  situation  of  their  openings  on  the  basal  joints  (coxae)  of 
one  of  the  pairs  of  limbs. 

The  Xiphosura  are  bisexual,  the  genital  ducts  opening  on 
both  males  and  females  on  the  posterior  surface  of  the  oper- 
culum near  its  base.  The  ovaries  are  much  branched  paired 
structures,  the  various  branches  frequently  anastomosing 
even  across  the  median  line.  The  testes  are  numerous 
spherical  bodies  scattered  through  the  body  and  situated  on 
branching  and  anastomosing  vasa  deferentia. 

Development  and  Affinities  of  the  Xip/ioswra.— When  tlio 
young  Limulus  leaves  the  egg  it  presents  a  remarkable  resem- 
blance to  a  Trilobite  and  suggests  a  possible  affinity  with 
these  forms  which  are  known  to  occur  only  in  the  Palaeozoic 
rocks.  In  these  same  rocks  there  occur  also  the  remains  of 
forms  known  as  the  Eurypteridce  which  seem  to  have  been 
even  more  nearly  related  to  Limidus  than  were  the  Trilobit(;s. 
In  them  the  cephalothorax  bore  apparently  only  six  pairs  of 
appendages  which  resembled  more  or  less  closely  those  of 
Zimvlus,  except  that  the  sixth  pair  was  broad  and  oarlike. 


TYPE  CRUSTACEA. 


433 


I,  the  sides 
n  being  iu 
ere  at  tbe 
erefore  be 
tide  which 

lediau  Hue 
ig.  195,  ol) 
u  function, 
ints  of  the 

'  of  large 
rax.  Each 
)f  a  papilla 
sal  joint  of 
)ular  organ 
d  complex 
ry  function 
brick-red  " 
indicating 
;s  (coxae)  of 

apening  on 
f  the  opev- 
hed  paired 
astoraosiug 
numerous 
situated  ou 

-When  the 
able  reseni- 
,ffinity  Avitli 
3  Palaeozoic 
remains  of 
have  beou 
3  Trilobites. 
six  pairs  of 
ly  those  of 
md  oarlike, 


probably  serving  for  swimming.  The  abdomen  was  com- 
posed of  twelve  segments,  the  anterior  six  of  which  were 
much  more  massive  than  the  others  and  bore  five  pairs  of 
platelike  appendages  on  whose  posterior  surface  were  the 
branchiae.  The  terminal  segment  bore  a  spine  or  fiulike 
structure.  Such  a  form  as  this,  represented  by  the  genus 
rterygotus  (Fig.  198),  presents  strong  similarities  to  Zimulus 
and  also  to  the  Scorpions,  bearing  out 
the  numerous  similarities  of  structure 
occurring  between  Zimidus  and  those 
forms.  This  side  of  the  affinity  may 
be  postponed,  however,  until  the 
next  chapter,  and  the  comparison  of 
Limidus  with  the  Crustacea  discussed 
here.  Its  chitinous  cuticle,  its  jointed 
and  biramous  appendages,  and  its 
branchial  respiration  show  similari- 
ties to  the  Crustacea,  as  do  also  the 
form  of  the  heart  and  the  compound 
eyes.  Whether  or  not  the  coxal 
gland  is  comparable  to  the  shell- 
gland  is  at  present  uncertain,  but  the 
other  similarities  are  sufficient  to 
justify  the  recognition  of  a  Crusta- 
cean   origin    for    Limulus.       It  iormi^  YmAm.—Pterygotus  angliens 

indeed  a  connecting  link  between  the  ^^'■°"*  Nicholson). 

Crustacea  and  the  Arachnida,  presenting  probably  on  the 
whole  more  affinities  with  this  latter  group  than  with  the 
former. 

Since,  however,  a  Crustacean  ancestry  is  probable,  a  com- 
parision  of  the  appendages  of  Limulus  with  those  of  a  repre- 
sentative of  the  ancestral  group  ought  to  be  possible.  It  has 
already  been  noticed  that  the  brain  of  Limulus  is  a  syncere- 
brum  composed  of  three  segments ;  it  represents,  therefore, 
two  segments  of  which  the  appendages  and  other  parts  have 
disappeared.  Furthermore,  recalling  that,  in  the  higher 
Crustacea  at  least,  a  ganglion  occurring  between  the  cerebral 
autennary  ganglia  iu  the  embryo  indicates   a  lost   pair    of 


'll, 


32"** 


434 


INVERTEBRA TE  MORPHOLOQ  T. 


Sip 
2- 

»: 

lie 


appendages  in  these  forms,  the  following  table  may  represent 
the  homologies  of  the  appendages  of  the  two  groups. 


Crustacean. 

Limulus. 

1  segment 

no  appendage 

no  appendage 

2 

•  *  •  • 

«          (( 

3 

antennules 

tt          (( 

4 

....  antennae 

chelicerae 

6 

mandibles 

1st  pair  of  legs 

6        ' 

1st  maxillsB 

2d     "     "    " 

7 

....2d      " 

3d     "     "    " 

8 

....  1st  thoracic  appendages 

4th  "     "    " 

9 

....  2d 

(( 

5th  "     "    '« 

.0 

....  3d 

« 

operculum 

LITERATURE. 

A.  Oerstaecker.    Crmtaeeen.  Bronn's  Klassen  und  Ordnungcn  des  Thierreichs 

Bd.  V.  1.  Abtb.,  1866-79. 
A.  S.  Packard.     The  Anatomy,  Histology,  and  Embryology  of  Limulus  poly- 

phemua.     Memoirs  Boston  Soc.  Nat.  History,  1880. 
E.  K.  Lankester.     Limulus   an  Arachnid.    Quarterly  Journ.   Microscopical 

Science,  xxi,  1881. 
8.  Watase.     On  the  Morphology  of  the  Compound  Eyes  of  Arthropods.    Studies 

from  the  Biol.  Lab.  Johns  Hopkins  Univ.,  iv,  1890. 
W.  Patten.     On  Vie  Origin  of  Vertebrates  from  Arachnids.    Quarterly  Journ. 

Microscop.  Science,  xxxi,  1890. 
J.  8.  Kingsley.     Tlie  Embryology  of  Limulus.    Journ.  of  Morphology,  vii 

1892 ;  viri,  1893. 
W.  Patten,     On  the  Morphology  and  Physiology  of  the  Brain  and  Sense-organs 

of  Limulus.    Quarterly  Journ.  Microscop.  Science,  xxxv,  1898. 


TYPE  ARACHNID  A. 


435 


y  represent 
ps. 

Limulus. 

appendage 
(( 

(( 

liceraB 

pair  of  legs 
((      «     « 

«      <(     « 

<(      «     (( 

«      ((     i( 

irculum 


5s  Thierreichs, 

Litnulua  poly- 

Microscopical 

pod*.    Studies 

arterly  Journ. 

•phology,  VII, 

I  Seme-organs 
893. 


CHAPTER  XIV. 

TYPE  ARACHNIDA. 

The  Araclmida  are  essentially  terrestrial  forms,  for  though 
a  few  species  lead  an  aquatic  or  marine  life,  they  are  evi- 
dently descendants  of  forms  which  led  a  terrestrial  existence 
and  have  only  secondarily  acquired  the  power  of  living  under 
water.  In  all  members  of  the  group  the  body  is  covered  by 
a  more  or  less  ^^  ick  chitinous  cuticle  and  the  appendages  nre 
as  a  rule  jointed. 

A  characteristic  feature  of  the  group  is  the  fusion  of  the 
head  and  thorax  to  form  an  unsegmented  cephalothorax  bear- 
ing usually  six  pairs  of  limbs.  The  first  pair  of  these  are 
the  chelicerce  (Fig.  201,  ch),  composed  of  one  to  three  joints 
aud  terminated  either  by  a  claw  or  a  chela  ;  they  lie  in  front 
of  the  mouth,  which  is  bounded  at  the  sides  by  the  basal 
joints  of  the  second  pair  of  appendages,  the  pedipalps  (pe), 
which  may  be  long  and  lind)like,  or  chelate,  or  in  some  cases* 
cluwlike,  their  basal  joints  serving  in  all  cases  as  mandibles. 
Behind  these  follow  four  pairs  of  legs  composed  of  six  or  seven 
joints,  the  basal  joint  being  termed  the  coxa,  the  next,  usually 
short,  the  trochanter,  the  third  the  femur,  the  next  two  to- 
getlier  form  the  tibia,  then  follows  in  some  forms  a  metatarHus, 
while  the  terminal  one,  provided  with  two  claws,  termed 
ungues,  and  in  some  mites  also  with  a  suctorial  disk,  consti- 
tutes the  tarsus.  Variations  from  this  structure  of  course 
occur,  the  chelicerir,  for  example,  in  some  mites  being  re- 
duced to  short  stylets,  and  in  others  the  two  posterior  pairs  of 
legs  maybe  quite  rudimentary  {/'ht/foptus).  The  most  imjmr- 
timt  variation  is,  however,  that  found  in  the  members  of  the 
order  Holifugu',  in  which  a  head  is  distinctly  marked  off  from 
a  thorax  composed  of  three  segments. 

The  abdomen  iu  some  loinis  is  segmented,  in  others  all 
trace  of  the  segmentation  is  lost,  and,  tinully,  in  the  Mites  it 


111 


436 


INVERTEBRATE  MORPHOLOGY. 


5- 


'1! 

JjS. 


may  be  united  with  the  cephalothorax.  In  the  Scorpions  it 
is  divisible  into  an  anterior  portion,  the  prseabdomeu,  much 
broader  and  stouter  than  the  posterior  postabdomen,  an  ar- 
rangement also  indicated  in  certain  other  forms.  In  the 
adults  the  abdomen  is  usually  destitute  of  appendages,  though 
they  may  be  present  in  the  embryos ;  the  Scorpions,  however, 
possess  two  highly-modified  pairs,  and  it  seems  probable  that 
the  four  or  six  papilliD  upon  which  the  ducts  of  the  spinning- 
glands  open  in  the  Spiders  represent  also  modified  append- 
ages. 

A  special  respiratory  system  is  entirely  wanting  in  a  few 
forms.  In  the  majority  there  occur  on  the  sides  of  the  body 
from  one  to  four  pairs  of  pores  termed  stigmata  (Fig.  201,  st^'^). 
In  the  Scorpions  and  some  other  forms  each  stigma  opens 

into  a   cavity    lined  with    cliitiu 
continuous  with  that  which  covers 
^    the  general  surface  of  the  body, 
f    and  into  this  cavity  there  project 
*  a   number  of    lamellae   arranged 
^  like  the  leaves   of   a  book  (Fig. 
^  199),  whence  the  term  lung-books 
frequently  applied  to  them.    Each 
lamella   is  hollow,  trabecular  ex- 
tending  across    the    cavity  troiii 
one  wall  to  the  other,    and    the 
cavities    communicate    with    tlie 
c<L'lomic  lacuu!i>,  so  that  blood  can 
readih'   flow   into    them    and    so 
cliange  its  gases  through  the  thin 
TiiRonim  TiiK  Li'No-BooK  OF  Avails  of   the  lamellro.      In  otln'V 
Sim DKK  (lifter  McLkod).  cases  there  occurs  in  connection 

ch  =  rliitino,j,'(Mious  tiHsue.  ^^itj^  the  lung-book  apparatus,  or 

ff  =  ImmIv  Willi.  ,  J-      1  1      •  -i  1 

,  ,■  ,       „  else   entirely  rei)  acing   it,  a  tia- 

«(  =  stigma.  choal  system  consisting  of  a  niini- 

t  =  lust   coinpnrtnipnt    of   Iupg:-  bor   of  tubes  ramif^'ing    thron^li 

book,   tiiid.ualikc  In  clmr-  tlio  l,ody.     Ill  some  cases  a  stron.^ 

tube  or  trachea  arises  at  each 
ntigiiiti  jxuii  iTaverses  tne  ixjily,  giving  s>ii  ijriiiiclieH  to  all  p.'ti'is 
as  it  goes ;  iu  others  there  is  iu  couueutiou  with  each  stigma 


Fio.  199.— TiiANHVEUSK    Section 


TYPE  AliACIINIDA. 


437 


icorpious  it 
)meu,  much 
neu,  au  ar- 
is.  In  the 
ges,  though 
IS,  however, 
obable  that 
le  spiuniug. 
ed  appeud- 

Dg  in  a  few 
)f  the  body 
g.  201,  st'-% 
igina  opens 
k'ith  chitiu 
hich  covers 
I  the  body, 
ip.re  project 
B  arranged 
book  (Fig. 
lung-books 
lem.  Each 
^beculfB  ex- 
!avity  troiii 
r,  and  the 
with  till) 
t  bh)od  ciiii 
111  aud  so 
gh  the  tliiii 
In  other 
connection 
)paratns,  or 
g  it,  a  tr;i- 
jj  of  a  nniii- 
ig  thr<iugli 
^ea  a  stroiii,' 
08  at  each 
to  all  parts 
mch  Htigniii 


a  bunch  of  unbranched  trachejB,  and  all  gradations  between 
these  two  conditions  occur.  The  trachea  are  lined  with 
chitiu,  which  is  sometimes  thickened  to  form  rings  or  spiral 
bands  which  serve  to  keep  the  lumen  of  the  tubes  open  and 
thus  permit  a  free  passage  of  air  into  them. 

The  ccfilom  is  tilled  for  the  most  part  with  the  various 
organs  and  is  reduced  to  a  series  of  lacunar  spaces  coutainiug 
blood,  sometimes  rich  iu  hiemocyauin  and  assuming  a  blue 
color  when  oxygenated.  A  heart  is  wanting  in  some  Mites, 
but  is  present  in  the  majority  of  forms,  varying  from  a  saclike' 
organ  with  a  siugle  pair  of  ostia  guarded  by  valves  to  au 
elongated  cylinder  with  as  many  as  eight  pairs  of  ostia  (Scorpi- 
ons). It  is  for  the  most  part  situated  iu  the  abdominal  region, 
and  in  the  Spiders  is  enclosed  within  a  space  with  detiuite 
walls  which  is  termed  the  pericardium,  though  it  civuuot  be 
considered  homologous  with  the  pericardium  of  the  Mollusca, 
since  it  contains  blood ;  muscle-bands  extend  from  it  to  the 
walls  of  the  body  and  by  their  contraction  cause  its  expan- 
sion, fibres  in  its  wall  diminishing  its  cavity  and  forcing  the 
blood  through  the  ostia  into  the  heart.  Arteries  in  many 
forms  arise  from  the  heart,  but  after  usually  a  short  course 
open  into  the  lacuuar  ccelom. 

The  digestive  tract  pursues  a  more  or  less  straight  course 
tlirough  the  body,  but  shows  a  tendency  to  develop  coical  oiit- 
^rowths  which  sometimes  reach  a  considerable  size.  The 
anterior  aud  posterior  portions  of  the  tract  are  ectodermal, 
while  the  middle  region  or  mid-gut  is  endodermal  and  is  the 
portion  with  which  tlie  creca  are  connected.  In  the  Hcorpi- 
ons  the  ducts  of  a  digestive  gland  open  into  the  mid-gut,  and 
in  many  forms  there  is  connected  with  the  posterior  i)ortion 
of  this  same  region  a  pair  of  tubuhir  Malpigliian  vessels 
which  are  presumably  excretory  in  function  and  recall  the 
simihir  structures  of  the  Amphipoda.  The  end-gut  is  fre- 
quently dilated  into  a  large  bladderlike  structure,  the  rectal 
I'hidder. 

The  nervous  system  consists  of  a  supra(A.'sophagoal  syn- 
cerebrum  composed  of  three  i)airs  of  ganglia  fused  together, 
anu  in  some  forms  even  four  pairs  may  be  included,  since  the 
chelicerro  may  be  innervated  from  the  mass,  their  ganglia  in 


438 


INVERTEBRATE  MORPHOLOGY. 


embryonic  life  being,  however,  distinct  and  postoral  in  posi- 
tion, only  later  mov'ng  forward.  The  succeeding  ganglia  are 
generally  mora  or  loss  fused,  and  indeed  in  some  forms  all 
the  ganglia  of  the  limb-bearing  segments  of  the  cephalothorax 
may  be  united  with  those  of  the  abdominal  region  to  form  a 
single  ganglionic  mass.  In  some  forms  a  single  ganglion 
occurs  behind  this  mass  at  the  junction  of  the  cephalothorax 
and  the  abdomen,  and  in  the  Scorpions  there  is  posteriorly  )i 
ventral  nerve-cord  with  seven  pairs  of  ganglia,  the  anterior 
pair  corresponding  Avitli  the  fifth  abdominal  segment.  A 
sympathetic  nervous  system  occurs  in  the  Scorpions,  Spiders, 
and  Harvest-spiders,  consisting  of  a  nerve  arising  from  the 
syncerebrum  and  passing  to  the  digestive  tract. 

Hairs  situatod  upon  the  body  and  appendages  serve  as 
sense-organs  of  touch  and  apparently  also  of  audition,  since 
Spiders  are  sensitive  to  air-vibrations  and  possess  no  definite 
auditory  organs.  Eyes  are  very  generally  present  and  vary 
considerably  in  number,  there  being  in  the  Spiders  three  or 
four  pairs ;  in  the  Scorpions,  in  which  there  are  from  two  to 
six  pairs,  one  pair  become  closely  approximated  on  each  side 
of  the  mid-line  and  recall  the  median  eyes  of  Limuliis,  while 
the  remaining  pairs  are  situated  more  to  the  sides  of  the 
cephalothorax.  In  structure  the  median  eyes  difler  from  the 
lateral  ones  ;  the  chitiuous  cuticle  is  thickened  over  them  to 
form  a  simple  uufaceted  lens  below  which  lies  a  layer  of 
transparent  cells  continuous  with  the  general  ectoderm  (hypo- 
dermis)  of  the  body  and  which  may  be  termed  the  corneal 
hy])odermis,  though  more  usually  they  are  known  as  the 
vitreous  cells.  Below  them  comes  the  retina,  consisting  of  a 
single  layer  of  elongated  cells  with  their  nuclei  situatcil 
toward  their  inner  ends,  with  which  the  fibres  of  the  optic 
nerve  come  into  (ionnection.  The  various  retinal  cells  Jiiv 
arranged  in  groups  of  five  (retinulaO,  which  secrete  a  tliiii 
chitinous  rod  upon  their  contiguous  faces,  ])roducing  tlius  a 
rhabdom  comjiosed  of  five  parts.  IJehind  the  retina  is  a  thin 
layer  of  cells,  the  postretinular  layer,  and  numerous  pigment- 
cells  occur  between  the  various  retinuhe.  The  latfual  eyes 
are  conHtructed  upon  a  very  different  [ilan,  lacking  a  coriie:i! 
hyiiodermis  between  the  retina  and   the   cornea.     They  niv 


TYPE  AliACimiDA. 


439 


al  in  posi- 
^anglia  are 
}  forms  all 
halothorax 
1  to  form  a 
9  gauglioii 
halothorux 
)steriorly  )i 
le  anterior 
gment.  A 
IS,  Spiders, 
I  from  the 

s  serve  as 
ition,  since 
no  definite 
b  and  var^' 
s  three  or 
t'om  two  to 
1  each  side 
iilus,  while 
les  of  the 
r  from  the 
3r  them  to 
a  layer  of 
3rni  (hypo- 
lie  corneal 
wn  as  the 
isting  of  ii 
li  situated 
'  the  optic 
I  cells  arc 
ste  a  tliiii 
ing  thus  a 
la  is  a  thill 
s  pigmeiil- 
iteral  eyes 
;  a  corneal 
They  arc 


cup-shaped  structures,  the  cavity  of  the  cup  being  filled  by 
the  cuticular  cornea  and  its  wall  transformed  into  the  retina 
\vhich  is  continuous  at  the  margins  of  the  cup  with  the  gen- 
eral hypodermis.     The  rethial  cells  are  of  two  kinds   viz 
large  sensory  cells  and  smaller  interstitial  cells.     Each  sen' 
sory  cell  is  surrounded  by  pigment  and  bears  upon  its  lateral 
walls  a  chitmous  secretion   which,  with   the    corresponding 
secretion  of  contiguous  cells,  forms  a  rhabdom.     The  nuclei 
of  the  cells  are  situated  nearer  their  inner  than  their  outer 
eiids,ciud  behind  them  in  Emeorpim  highly  refractive  spheres 
occur   imbedded   in    the    cells,  constituting   what  have  been 
termed  the  phaospheres.     Upon  its  inner  wall  the  retina  is 
Inied  by  a  basement-membrane  continuous  with  that  lyin.r 
below  the  general  hyi)odermis  and  perforated  by  the  fibres  o'f 
the  optic  nerves  which  come  iuto  contact  with  the  inner  ends 
of  the  sensory  cells. 

In  the  Spiders,  in  which  there  are  six  or  eight  eyes  arranged 
upon  the  dorsum  and  sides  of  the  cephalothorax,  the  ante- 
rior dorsal  pair  differs  in  structure  from  the  remaining  ones 
In  both  forms  of  eyes  (Fig.  200)  the  cuticular  cornea  (c)  rests 


F.H.  m-EvK8  OK  SnuKu.    A,  Antkmk.u,  ani,  Ii,  PosTKHKm  Eye  (after 

Hkhtkau  from  KniisdiiKi/r  and  Mkidkui. 
b  =  rods.  ,.  =  ,.,,,i,„^ 

'  =  •'-'"'*•  t  =  i.'ipttum  lucidiun. 

V  =  vitreous  layei. 

upon  a  corneal  hypodermis,  (the  vitreous  culls,  v\  but  the 
airangement  of  the  retina  differs  greatly.  In  the  anterior 
<i<'isul  pair  (A)  it  is  composed  of  a  layer  of  elongated  cells  (r) 


Mi,> 


5e 


^vhose  nuclei  are  situated  towards  tl 


eir  inner  ends,  while  near 


440 


INVERTEBRA  TE  MORPUOLOG  Y. 


the  outer  ends  are  situated  a  uumber  of  rodlike  bodies  (rliab- 
doms,  h),  whence  these  eyes  have  beeu  termed  prebncilhir ; 
the  nerve-fibres  are  continuous  with  the  inner  ends  of  the  cells. 
In  the  posterior  dorsal  and  lateral  eyes  (/>*)  an  inversion  of 
the  retina  (?•)  has  taken  place,  so  that  the  rods  (J))  are  situated 
at  the  apparently  inner  ends  of  the  cells  and  the  nuclei  at 
their  outer  ends,  whence  the  term  postbacillar  applied  to 
these  eyes.  The  optic  nerve-fibres  enter  at  the  sides  of  tlic 
eye  and  are  distributed  to  the  nuclear  ends  of  the  retinal 
cells,  recalling  the  arrangement  occurring  in  Feden  among  the 
Mollusca.  The  innermost  layer  of  the  eye  upon  which  the 
ends  of  the  rods  rest  is  cellular,  numerous  minute  crystals 
being  deposited  in  the  cells,  whence  it  has  the  function  of  a 
reflector  and  is  termed  the  tapetuni  it).  It  is  quite  wanting  in 
the  prebacillar  eyes. 

The  signiflcanee  of  the  structure  of  tlio  Araclinid  eye  may  be  under- 
stood by  siijtposing  it  to  have  been  derived  from  u  compoiiiid  eye  similar  tn 
that  of  LiiiiulNs  (sec  p.  4;U),  tlie  iiidividiialities  of  the  various  ommatidia 
being  more  or  less  sul)ordinated.     The  cuticular  cornea  in    Liiniiliis  i.> 
smooth  upon  its  outer    surface,  the  inner  surface  'oeing  produced   intd 
papilke,  one  of  which  corresponds  to  eacli  ommatidium.     In  the  Arachnids 
even  these  papillie  are  wanting,   (he  cornea  showing  no  evidence  of  tlic 
j)rescnce  of  ommatidia.     The  lateral  eyi's  of  the  Scorpions  aiti)roach  moio 
nearly  in  their  general  structures  the  eyes  of  Liinuliis,  though  the  conden- 
sation of  the  ommatidia  has  been  carried  further  than  in  tlie  median  eyes 
of  that  form,  or  in  the  posterior  dorsal  and  lateral  eyes  of  (he  Spiders.     But 
in  these  eyes  the  condensation  is  associated  wi(h  an  invagination  of  the  en- 
tire eye,  a  process  which,  it  may  be  remarked,  is  indicated  in  the  niedi;m 
eyes  of  Limidnn.    Tills  invagination  has  been  regarded  as  a  pushing  in, 
under  and  parallel  to  (he  liypcxhu-mis,  of  a  pouch  of  tliat  layer,  a  prucc,>> 
which  gives  in  cross-sec(i()n  the  appearance  of  an  S-shaped  fold.     The 
outermost  layer  of  the  fold  forms  the  vitreous  cells  or  corneal  liypoderniis, 
the  middle  layer  (he  retina,  the  inversion  of  whicli  is  plainly  seen  in  (lie 
])os(erior  dorsal  and  laleral  eyes  of  (he  Spiders,  while  I  lie  innermost  layer 
forms  the   postretinal   layer   in   (he   Scorpions  and    (he  tapetuni   of  the 
jSpiders.    The  ommatidial  re(inuh«  are  more  or  less  retained  in  these  eyes, 
as  is  shown  by  the  structure  of  (he  rhabdom,  which  in  (he  Scorpions  i> 
composed  of  five  ])ar'-,  ui  the  Spiders  of  two,  and  in  the  Harvest -spid'V-^ 
of  three.     The  auteei  )r  dorsal  eyos  of  the  Spiders  do  not  seem  to  li,i\e 
undergone  an  invi^ination,  hence  the  absence  of  a  tnpetum  and  (he  pra'ba- 
cillar  structure  of  the  retina;  a  corneal  hypodcirmis  is,  however,  preseni. 
and  would  seem  t"  wdicate  an  invagination,  but  its  mode  of  orighi  seems 
at  present  but  imj>ori  'etiy  understood.    If  ageneraliza(iou  is  to  be  iiiaile,  it 


TYPE  ARACUNIDA. 


441 


will  be  to  the  effect  tha.  the  eyes  of  the  Arachnids  have  been  derived  from 
compound  eyes  simihir  to  those  of  Limulus,  and  tiiat  in  the  median  eyes  of 
tlie  Scorpions,  and  the  posterior  dorsal  and  lateral  eyes  of  the  Spiders  the 
entire  optic  area  has  been  invaginated,  making  them  comparable  to  the 
median  eyes  of  Llmulus,  while  the  lateral  eyes  of  the  Scorpions  and  the 
anterior  dorsal  eyes  of  the  Spiders  liave  not  undergone  invagination  and 
hence  are  comparable  to  the  lateral  eyes  of  Limnlus.  Whether  the  com- 
parability indicates  also  the  homology  from  a  phylogenetic  standpoint  of 
eye  to  eye  must  remain  at  present  uncertain  (see  p.  457). 

In  cidditioii  to  the  Malpishian  tubules  already  meutioued 
as  excretory  organs  occurring  in  connection  with  the  digestive 
tract^  of  the  Spiders,  there  exist  in  many  forms  additional 
glands  which  probably  are  also  excretory  in  function  or  sig- 
niticauce.  These  are  the  coxal  glands,  so  called  on  account  of 
their  openings  when  present  being  on  the  basal  joints  (coxro) 
of  one  of  the  pairs  of  legs.  In  the  Scorpions  and  Spiders 
the  ducf;S  of  the  glands  open  on  the  third  pair  of  legs  (i.e.,  the 
fifth  pan-  of  appendages)  in  the  embryo,  but  are  usually 
wanting  in  the  adults.  In  the  Solifugic  and  Harvest-spiders 
coxal  glands  also  occur  in  connection  with  the  fourth  pair 
of  legs,  and  similar  glands  have  also  been  observed  in  several 
genera  of  Mites,  opening,  however,  at  varying  points. 

Glands  are  also  of  frequent  occurrence  in  connection  with 
the  pedipalps,  having  apparently  varying  functions  in  differ- 
ent genera.  They  do  not,  however,  seem  to  belong  to  the  same 
category  as  the  coxal  glands  and  are  in  no  case  excretory. 

The  Arachnida  are  bisexual  throughout.  The  ovaries  not 
infrequently  fuse  to  form  a  single  mass  or  a  circular  band, 
and  in  connection  with  the  oviducts,  which  are  in  direct  com- 
munication with  them,  there  is  usually  developed  a  receptac- 
nlum  seminis,  and  in  the  Harvest-spiders,  an  elongated  ovi- 
]H)sitor.  The  testes  are  also  frequently  fused,  and  the  vasa 
deferentia  are  provided  with  vesicuho  seminales  and  usually 
terminate  in  a  copulatory  organ.  The  majority  of  forms  are 
oviparous,  excepticms  to  the  rule  beiug  found,  however,  as  in 
tlie  genus  Phrynus  and  in  the  Scorpions,  which  are  viviparous. 

1.  Order  Scorpionida. 
In  the  Scorpions  (Fig.  201)  the  body  is  composed  of  an 
uusegmeuted    cephalothorax    and   an    elongated   segmented 


Ml 

«ll 


:1 

1^' 


,-itai» 


442 


INVERTEPRA TE  MORPIIOLOO  Y. 


abdomen.  The  seven  anterior  segments  (the  prfeabdomen) 
of  the  abdomen  are  broader  and  thicker  than  the  remaining 
five  segments  (the  postabdomeu),  the  last  one  of  which  ter- 
minates in  a  curved  stout  spine  which  bears  at  its  extremitj' 
the  openings  of  two  ducts  leading  from  a  pair  of  glands  lying 
in  the  twelfth  abdominal  segment  and  secreting  a  poisonous 
liuid. 

The  chelicerre  (c/i)  are  small  chelate  appendages  situated 
in  front  of  the  mouth,  while  the  pedipalps  {pe)  are  long  and 

provided  with  strong  chelae,  their 
basal  joints  and  those  of  the  two 
succeeding  appendages  surround- 
ing the  mouth  and  serving  as  jaws. 
The  four  pairs  of  appendages  be- 
hind the  pedipalps  are  all  similar 
in  form,  being  six-jointed  walking- 
limbs.  Upon  the  abdomen  modi- 
tied  appendages  are  also  found, 
the  second  abdominal  segment 
bearing  a  pair,  each  member  of 
Avhich  consists  of  a  single  joint 
whose  posterior  edge  is  beset  Avith 
a  number  of  processes  which  give 
it  the  appearance  of  a  comb, 
whence  the  name  pectines  [pt) 
applied  to  these  appendages.  In 
front  of  the  pectines  lies  the  geni- 
tal opening,  protected  by  a  small 
genital  operculum  {op)  which  may 
possibly  represent  another  pair  ol 
appendages  belonging  to  the  first 
abdominal  segment. 

Upon  the  ventral  surfaces  of 
third,  fourth,  fifth,  and  sixth  abdominal  segments  elongated 
pores  are  to  be  found  which  are  stigmata  {sV'*)  leading  into 
the  respiratory  cavities  containing  the  lung-books,  of  which 
there  are  in  all  four  pairs  in  this  group.  No  tracheae  occur. 
The  intestine  is  quite  straight  in  the  Scorpions  and  laclvs 
cffical  outgrowths  excepting  the  two  Malpighian  tubules  sit- 


FlG.  201.— SCOUPION  (after  Owen). 
c>..  =  clielicerae. 
op  =  genital  operculum. 
pe  =  pedipalp. 
pt  =  pecten. 
«('-■*  =  stiffuiata. 


TYPE  AnACHNIDA. 


443 


uated  at  the  posterior  eucl  of  the  mid-gut.     The  digestive 
gland  18  a  large  live-lobed  structure  which  empties  through 
several  ducts  into  the  mid-gut. 
^    The    nervous    system    consists   of  a   syncerebrum   lying 
aoove  the  cesophagus  and  giving  rise  to  nerves  for  the  eyes 
and  for  the  chelicerae.     It  is  connected  with  a  suboesophageal 
mass  from  which  the  pedipalps  and  the  three  anterior  legs  are 
innervated,  the  fourth  pair  of  legs  receiving  its  nerves  from  a 
pair  of  distinct  ganglia  separated  only  by  a  short  distance 
from  the  suboesophageal  mass.     Behind  this  in  the  abdomen 
IS  a  chain  consisting  of  seven  pairs  of  ganglia  united  by  long 
connectives.     The  eyes  vary  in  number  from  two  to  six  pairs 
one  pair  being  situated  on  or  near  the  median  line,  while  the' 
others  are  lateral. 

Coxal  glands  occur  in  connection  with  the  third  pair  of 
legs,  and  the  heart  is  an  elongated  structure  lying  in  the  an 
tenor  portion  of  the  abdomen  and  possessing  eight  pairs  of 

OStlJX, 

The  Scorpions  are  viviparous.  The  ovaries  are  situated 
m  the  anterior  abdominal  region  and  are  elongated,  that  of 
one  side  of  the  body  being  united  with  the  other  by  several 
transverse  connections.  The  oviducts,  which  are  short,  serve 
as  uteri,  and  open  to  the  exterior  by  a  single  median  opening 
situated  on  the  ventral  surface  of  the  first  abdominal  segment 
Ihe  testes  consist  of  four  tubes,  those  of  the  same  side  bein- 
connected  by  transverse  anastomoses,  and  unite  together  to 
open  into  a  protrusible  penis,  accessory  glands,  vesicuhe  sem- 
males,  occurring  in  coniic-ction  with  each  vas  deferens  The 
single  genital  orifice  occupies  the  same  position  as  in  the 
temale. 

The  Scorpions  are  confined  to  the  warmer  regions  of  the 
globe,  but  few  genera  being  known.  Of  these  the  genera  Eu- 
■scorpius  and  Buthm  are  perhaps  the  commonest 


tHttk 
'■IM 

IRliifei 

';* 


;;i53 


2.  Order  Pseudoscorpionida. 

This  order  includes  a  number  of  small  forms  which  are 
found  under  the  bark  of  trees  or  among  dead  leaves  or  moss 
one  genus,  Chelifer  (Fig.  202),  occurring  occasionally  between 


444 


IN VEUTEBHATE  MORPIIOLOO  Y. 


the  pages  of  books,  aud  lieuce  being  known  popularly  as  the 
Book-scorpion.  The  cephalothorax  is  unsegmented,  and  is 
followed  by  a  broad  flattened  abdomen  composed  of  eleven 
segments.  A  prseabdomen  and  a  postabdomen,  such  as  can 
be  distinguished  ';i  the  Scorpionida,  does  not  occur,  nor  is 
there  a  terminal  poison-spine  nor  a  poison-gland. 

The  chelicene  and  pedipalps  resemble  those  of  the  Scor- 
pions, beiuf.'  chelate,  and  the  four  succeeding  appendages  are 

walking-legs,   while    the  abdomen    pos- 
^tL      sesses  no  appendages  in  the  adult.    Both 
Si    the    secon(l    and    third   abdominal    seg- 
ments bear  upon  their  ventral  surfaces  a 
pair  of  stigmata  which  are  the  openings 
of  tubular  trachetxi  which  extend  througli 
the  body  sending  otf   branches,  except 
in    Cherncs,  in   which   bunches    of   un- 
brauched  tracheae  arise  from  each  stig- 
ma.    A  heart  is  present,  but  consists  of 
Fiu.  202.— Chelifer  card-  a  siniple  tube  with  either  a  single  pair 
H(?/(/es(fio.n(:iiviKR).         Qf    (^ytia    near    its   posterior   extremity 

(Olnshun)  or  with  four  ostia  {Chernes). 
The  endodermal  portion  of  the  digestive  tract  gives  rise 
to  a  pair  of  lateral  ctecal  diverticula  branched  at  the  apex  and 
to  one  unpaired  ventral  one.  Two  eyes  are  present  in  Chelifer 
and  four  in  Ohisium,  Avhile  they  are  entirely  wanting  iu 
Chernes.  The  reproductive  organs  open  upon  the  ventral  sur- 
face of  the  second  abdominal  segment,  and  the  opening  is 
surrounded  with  glands  which  secreve  a  fluid  which  quickly 
hardens  to  silky  lilaments  and  serves  to  fasten  the  eggs  to 
the  abdomen  of  the  parent.  These  glands  are  hypodermnl  iu 
origin  and  correspond  to  the  spinning-glands  of  the  Spiders. 


3.  Order  Solifugse. 

The  members  of  this  order  are  characterized  by  the  head- 
region  being  separated  from  a  thorax  consisting  of  three  se.u- 
ments  and  bearing  the  three  posterior  pairs  of  legs.  TIih 
abdomen  is  also  segmented,  its  ton  sognicnts  showing  no  dit- 
ferentiation  into   pr«3abdomen  and  postabdomen,  nor  does  it 


TYPE  ARACIINWA. 


445 


i  openings 


possess  any  sting  or  poison-gland.    The  chelicenc  are  chelate 
but  the  pedipalps  are  long  and  leglike  and  possess  glands 
which  in  Galeodes  have  been  supposed  to  be  poisonous.     The 
anterior  pair  of  legs  lacks  the  terminal  ungues  found  on  tho 
others,   and  functions  as  a  second 
pedipalp  rather  than  a  walkiiig-leg. 
No  appendages  occur  on  the  abdo- 
men. 

Three  pairs  of  stigmata  occur 
on  the  ventral  surface  of  the  body, 
the  most  anterior  ])air  being  situ- 
ated on  the  lirst  thoracic  segment, 
while  the  other  two  are  on  the 
second  and  third  abdominal  seg- 
ments. The  anterior  position  of  the 
first  pair  is  probably  to  be  regarded 
as  secondary,  and  produced  by  a 
forward  migration  of  the  pair  which 
should  occur  upon  the  first  abdomi- 
nal segment.  The  stigmata  lead  ^'^'  ^^^-—Gnleodes  spinipalpus 
into  tubular  trachese  which  branch  ^f'o'"  clviku,. 

extensively.     A  comparatively  simple  heart  is  situated  in  the 
abdomen. 

The  mid-gut  possesses  numerous  branched  diverticula  as 
well  as  Malpighian  tubules.  The  nervous  system  consists  of 
a  syncerebrum  connected  with  a  subu-sophageal  mass  which 
represents  all  the  thoracic  and  abdominal  ganglia  fused  to- 
gether. Two  eyes  are  present,  situated  on  a  common  eleva- 
tiou  at  the  front  edge  of  the  head. 

The  reproductive  organs  resemble  those  of  the  Scorpions 
except  that  transverse  anastomoses  do  not  occur,  and  the  oen- 
ital  opening  is  situated  upon  the  ventral  surface  of  the  Srst 
abdominal  segment. 

The  Solifugno  is  a  small  order  living  more  especially  in 
warm  sandy  regions.  They  are  usually,  on  rather  insufficient 
grounds,  supposed  to  be  capable  of  inflicting  a  poisoned 
wound.  Only  two  genera,  Solpuga  and  (kdeodes,  belon-  to 
the  order. 


I 

5 


•5!: 


nor  does  it 


446 


IN  VEIiTEDliA TE  MOliPUOLOQ  Y. 


4.  Order  Pedipalpl. 

The  order  Pedipal[)i  includes  two  genera,  Phrynua  and 
Thelyphonm,  both  of  which  are  inhabitants  of  the  warmer 
regions  of  the  earth.  The  cephah)thorax  is  unseginented  ; 
the  abdomen  in  Phrynus  is  eh)ngated  and  oval,  and  conn)osed 
of  eleven  segments  showing  little  differentiation  of  form, 
while   in    Thelyphoniis   there   are   twelve    segments,  the   last 

three  of  which  are  much  smaller  than 
the  others  and  bear  a  long,  many- 
jointed  terminal  filament.  The  cheli- 
cera3  are  not  chelate,  but  the  terminal 
joint  may  be  Hexed  upon  the  basal 
one  and  contains  the  duct  of  a  poison- 
gland  which  opens  at  its  extremity. 
The  pedipalps  in  Phrynus  are  long 
and  leglike,  though  richly  provided 
with  spines,  and  terminate  with  un- 
gues, but  in  Thelyphonus  they  are  rel- 
atively short  and  stout  with  a  flexible 
terminal  joint  as  in  the  cheliceru' ; 
in  both  genera  the  basal  joints  of  the 

,  ,      ,  two    pedipalps  are   fused.      The    iirst 

datus  (from  CuviER).  •        ■  i       n        t 

leg  IS  long  and  slender  and  termi- 
nates in  a  filament-like  structure,  the  other  three  pairs  being 
typical  walking-legs. 

Four  stigmata  occur,  one  pair  situated  in  the  second  and 
another  in  the  third  abdominal  segment,  and  they  open  into 
cavities  containing  lung-books.  The  digestive  tract  is  com- 
paratively simple,  but  the  nervous  system  shows  a  concentra- 
tion of  the  postcjesophageal  ganglia  similar  to  that  described 
for  the  Solifugffi,  except  that  a  single  pair  of  ganglia  occurs 
in  the  abominal  region  united  by  long  connectives  with  tlm 
cephalothoracic  mass.  Eight  eyes  are  present,  two  of  whicli 
are  larger  than  the  others  and  situated  at  the  anterior  edj^v 
of  the  dorsal  surface  of  the  cephalothorax,  while  the  other 
three  pairs  are  situated  laterally^ 

The  reproductive  organs  are  paired  and  open  by  a  median 


TYPE  ARACHNID  A. 


447 


orifice  situated  on  the  ventral  surface  of  the  first  abtlomiual 
segment.     J*hrynus  is  vivipairous. 


r>.  Onlur  Phalangida. 

Tlie  Phalangida  (Fig.  205),  popularly  known  as  the  Harvest 
.s|)iders,  possess  an  unsegiuented  cephalothorax  (ct)  and  have 
from  six  to  nine  segments  composing  the  abdomen  {ah).  The 
<!lielicera3  are  chelate,  while  the  pedipalps  (pe)  are  long  and 
leglike,  Avith  terminal  ungues.  The  eight  walking-legs  are 
usually  exceedingly  long,  though  in  the  genera  Cyphophthahnm 
and  Gibbocellum  they  are  shorter..  A  single  pair  of  stigmata 
are  usually  all  that  occur ;  they  are  situated  upon  the  first 


ab  =  abdomen. 


Fig.  20^.— Letobtimtm. 
ct  =  cephiilothorax. 


pe  =  pedipalps. 


abdominal  segment  and  open  into  branching  trachefx?.  In 
(nhhocellum,  however,  two  pairs  occur,  situated  upon  the 
second  and  third  abdominal  segments,  the  anterior  pair  open- 
iug  into  branched  tracheae,  while  a  bunch  of  simple  unbranched 
trachea)  arises  from  erch  of  the  posterior  ones.  The  heart 
IS  somewhat  elongated  and  possesses  three  pairs  of  ostia  ;  ar- 
teries are  entirely  wanting,  the  blood  passing  from  the  heart 
directly  into  the  lacunar  spaces. 

The  digestive  tract  dilates  into  a  sac-like  stomach  from 
wliicli  numerous  much-branched  cfecal  diverticula  pass  off. 
Malpighian  vessels,  two  in  number,  are  found  in  ( 'yphophthal- 
nius  and  GMocellum,  and  have  been  described  as  occurrmg 


448 


IN  VERTEBRA TE  MORPIIOLOO  T. 


in  other  forms  also,  though  it  is  probable  that  two  glandular 
tubes  which  o})eu  to  the  exterior  ou  the  sides  of  the  cepl'alo- 
thorax  have  iu  some  forms  been  mistaken  for  these  organs. 
Odoriferous  glands  are  also  found  in  the  abdomen  of  some 
forms,  and  so-called  salivary  glands  occur  in  connection  with 
the  pedipalps. 

The  nervous  system  shows  a  marked  concentration  of  tlio 
postoral  ganglia,  a  single  })air  only  remaining  separate  from 
the  fused  mass  formed  of  the  reniainder.  The  majf)rity  of 
forms  possess  but  a  single  pair  of  eyes  ou  the  dorsum  of  the 
o(4)halotliorax,  but  in  Gihbocdlum  two  lateral  pairs  aro 
found. 

Ooxal  glands  have  been  described  in  connection  with  tlic 

coxal  joints  of  the  third  pair  of  legs  and  have  been  observed 

to  communicate  with   the  exterior,   diifering  therefore  from 

those  of  other  Arachnoids  in  being  functional  in  the  adult. 

The   reproductive  organs   are    unpaired,   a   condition  which 

results  from  tiie  fusion  of  originally  paired  structures,  and 

the  genital   pore  lies  in  both  sexes  at  the  juncti(m  of  tlio 

cephalotliorax  and  abdomen  or  on  the  first  abdominal  sc;^- 

ment.     The  vasa  deferentia  and  oviducts  are  paired,  each  of 

the  former  communicating  with  a  protrusible  penis,   whiln 

simihulyeach  oviduct  unites  with  a  long  ])rotrusible ovipositor. 

Certain  genera  such  as  Leiohunum.  (Fig.  20;")),  Phahmjium, 

and  Opilio,  are  exceedingly  common,  and  to  them  the  terms 

Harvest-m(Mi,  Harvest-spiders,  or  Daddy  Longlegs  are  i)o|>ii- 

larly  applied.     Other  forms,  such  as  (umiilcptiis,  with  spinoso 

jHMlipalps,  are  tropical  in  habitat,  whih^  CijphophfjKfJmm  aiid 

(iibhiK'cUum  have  a  limited  distribution,  and  on  account  of  tho 

many  diflnrences  of  structure  which  they  present  when  com. 

jmred  with  other  forms  are  sonu^times  grouped  together  to 

form  a  s(>parate  order.     It  is  to  be  noted  especially  that  these 

two  forms  possess  upon  the  second  abdominal  segment  a  ]i;iir 

of  wartlike  elevations  at  tho  summit  of  which  the  ducts  df 

numerous  spinning-glands  o])en. 

G.  Order  Araneae. 

The   order   Araneie   includes   a   large   number   of  forms 
possessing  very  tleJinite  characteristics.     The  ceplialothoi.ix 


TYPE  ARACHNID  A. 


449 


is  uusep;menteil,  as  is  also  the  abcloinen,  which  is  an  oval, 
si)herieal,  or  sometimes  irreguhirly-shaped  region  wliich 
narrows  suddenly  anteriorly  so  as  to  be  much  narrower  than 
the  cephalothorax.  The  chelicerfe  project  somewhat  in  front 
of  the  cephalothorax  and  each  consists  of  a  broad  basal  joint 
iiiid  a  terminal  strong  claw  which  may  be  Hexed  upon  the 
basal  joint,  and  has  opening  at  its  tip  the  duct  of  a  poison- 
ghmd  (Fig.  200,  p(j)  which  lies  in   the  cephalothorax.     The 

ht,  dK 


spg   ''■*         tr 

FlO.  30G.  — DlAGUAM   OF   STnUCTUIlE    OF   A    SlMPKIi  'Hftcr  LkitkAHT). 


iio  =  aorta. 
ce  —  cerebral  ganglion. 
ch  =  c'lielicera. 
(Iff  =  digestive  ginnd. 
gp  =  genilal  pore. 
ht  =  heart. 
l/j  =  liing-l)ook. 
int  =  M;iii)igliian  tul)nle. 
oc  =  eye. 
ov  =  ovary. 


J)e  =  |)eili|ijil|). 
Pff  ■-  poison  gland. 

rb  =  rectal  liladder. 

rs  =  receptucuhmi  seminis. 
«  =  stomach. 

sd  =  stomaeii  <iivertieiiliini, 

A/>  =  spinneret. 
»pg  =  spinning  glands. 

tff  -  tlionieie  ganglion. 

ir  =  trachea. 


p((lipalp;-i  of  the  fen)ales  are  leglike  structures  usually  with  a 
terminal  unguis,  but  in  the  male  are  more  or  less  swollen  to 
serve  as  ticcessory  organs  in  copulation.  The  four  pairs  of 
seven-jointed  legs  are  all  simihir  in  structure  and  serve  for 
walking,  dilToring  in  relative  length  v.\  ditierent  genera.  In 
thti  emlu-yc  the  abdomen  is  distinctly  segmented  and  bears 
five  or  six  pairs  of  rudimenl.iry  ap])endages,  the  more  ante- 
rior of  wiiicii  later  disappear,  while  the  two  or  three  postcn'ior 
pairs  persist  as  the  spinnerets  («/)),  so  called  from  the  occur- 
rence on  tlieni  of  the  openings  of  the  ducts  of  the  spinning- 
elands  (HpcfX 

These  are  very  numerous  and  oj)en  at  the  apices  of  the 
spinnerets,  eiuh  gland  i)rodiiciug  a  fluid  .secretion  which 
ouiekly   l.-.nh--   i^^^   exposure   to  the  air    io  f,,rm    a   silken 


I 


450 


INVFAITEBRA  TE  MOIiPUOLOG  T. 


thread.     The  thickuess  of  the  thread  may  be  modified  by 
uuitiug  together  the  secretions  of  a  greater  or  less  number  of 
the  glauds,  which,  moreover,  differ  amoug  themselves,  some 
producing,  for  instance,  a  sticky  secretion  with  which  certuiu 
of  the  threads  may  be  covered.     In  some  forms  there  is  situ- 
ated upon  the  abdomen  just  in  front    of   the    spinnerets   ,t 
chitinous  plate,  the  crihellum,  which  is  perforated,  like  the 
spiunerets,  by  the  ducts  of  numerous   spinning-glands.    Its 
])reseuce  is  associated  with  that  of  a  calamistriim,  a  peculiar 
modification  of  the  metatarsus  of  the  last  pair  of  legs,  it  beiu"' 
furnished  with  a  double  row  of  bristles  which  are  rapitllv 
waved  over   the   cribellum    and  draw  from  its  glands  their 
secretion.     Tlie  threads  are  used  for  several  purposes,  as,  for 
example,  to  fasten  the  ova  to  the  body  of  the  parent  or  to 
form  a  cocoon  for  them,  or  else  to  form  a  snare  by  which 
insects  may  be  caught  to  serve  as  food.     These  snares  iu 
some  cases  are  composed  of  an  irregular  network  of  threads 
arrauged  without  any  definite  pattern,  as  in   Theridium,  ])iit 
some   other  forms   show  a  certain  amount  of  architectnnil 
skill,  weaving  a  i)latform  of  felted  threads  which  tenninatcs 
in  a  tubelike  place  of  concealment  for   the  spider  (e.g.,  ^b/r. 
letia,  Tegenaria)  or  webs  composed  of  threads  radiating  fioiu 
a  central  point  and  united  by  other  threads  arranged  in  a 
spiral  or  in  concentric  circles  (e.g.,  hpeim,  the  common  gardm- 
spider),  or  else  using  the  threads  to  form  a  hinged  trap-door 
covering  in  a  burrow  in  the  earth  which  serves  as  a  doniicilf 
as  in  the  Tra})-(K)or  Spider. 

The  digestive  tract  exjjands  in  the  thoracic  region  into  a 
saclike  structure  (.v)  from  each  side  of  which  thive  or  jiioic 
usually  five  ca'cal  diverticula  (.sd)  arise,  the  anterior  pair 
sometimes  anastomosing  so  as  to  form  a  ring,  while  in  souk; 
cases  {Epaiva)  secondary  diverticula  (>xt(>nd  from  tlu!  iiioiv 
postiu'ior  ones  into  tiie  coxal  joints  of  the  legs.  In  the  ahdo- 
mon  the  intestine  is  more  cylindrical,  giving  rise  to  niurli- 
branched  lateral  div<Mticula  whicii  together  form  tlie  so-cnllfd 
liver  {(hf),  and  having  connected  witli  it,  just  as  it  joins  tlio 
end-gut,  two  elongated  Malpighian  tubules  (////).  The  eiitl- 
gut  itself  dilates  into  a  largo  rectal  bladder  {rl>)  which  a  short 


TTPE  ARACHNID  A. 


451 


modified  by 
ss  number  of 
iselves,  some 
vliich  certuiu 
there  is  sitii- 
spinnerets  ;t 
ted,  like  the 
-glauds.  Its 
m,  a  peculiiir 
legs,  it  being 

are  rapidly 
glands  their 
poses,  as,  for 
parent  or  to 
re  by  which 
3e  snares  iu 
k  of  threads 
wridium,  l>iit 
irehiteotnral 
li  termiuatfs 
er  (e.g.,  Jr/r- 
diating  fioiu 
•ranged  in  a 
mon  garden- 
ed  tra])-door 
iS  a  domicile 

Bgiou  into  a 
ive  or  jnoi't' 
iiterior  pair 
lile  in  soino 
a  the  molt' 
[n  the  abdo- 
^o  to  nitifli- 
;he  Ho-ciillt'd 
it  joins  (he 

,       TllO    (Mld- 

liich  H  short 


rectum  connects  with  the  anus  situated  at  the  posterior  ex- 
tremity  of  the  body. 

In  the  genus  iMygale  and  allied  f..rms  two  pairs  of  stig- 
mata are  found  near  the  anterior  portion  of  the  abdomen, 
l)oth  of  which  lead  into  cavities  containing  lung-book.s! 
In  the  majority  of  forms,  however,  bat  one  pair  of  luirg-books 
(U))  occurs,  the  second  pair  of  stigmata  opening  into  a  tracheal 
tube  {tr)  extending  into  tlie  cei)halothorax  and  terminating  in 
a  bunch  of  unbraached  trachere,  a  similar  bunch  arising  near 
its  base  and  extending  backwards  into  the  abdomen  {Seges- 
tria).^  In  some  iovivn  the  second  or  tracheal  stigmata  may 
be  situated  far  back  upon  the  abdomen,  and  may  be  united 
to  a  single  median  transversely-elongated  cleft,  from  which  a 
l)unch  of  unbraached  {Aftus)  or  branched  trachese  aiises. 

The  heart  {ht),  which  lies  in  the  abdomen,  is  enclosed 
Mithiu  a  so-called  pericardium  and  possesses  three  pairs  of 
ostia.  It  is  continued  anteriorly  and  posteriorly  into  aorta', 
and  gives  off  also  lateral  arteries,  all  of  which  open  after  rel- 
atively short  courses  into  the  lacunar  spaces.  T]ie  blood  is 
returned  u)  the  pericardial  cavity,  whence  it  passes  into  the 
lieart,  the  greater  portion  on  its  way  to  the  pericardium  pass- 
ill,!;-  through  tJie  lung-books. 

The  nervous  system  consists  of  a  syncerebrum  (ee)  and  a 
Jarge  cephalothoracic  ganglionic  laass  [tg].  In  addition  to 
the  nerves  to  tlie  appendages,  a  posterior  nerve  arises  from 
this  mass  and  })asses  backwards  towards  the  abdomen,  in 
Mugnh'  dilating  at  the  junction  of  that  region  with  the  cephalo- 
thorax  into  a  pair  of  small  ganglia.  A  sympathetic  or  visceral 
bvstcm,  ccmsisting  of  a  nerve  arising  l)y  paired  trunks  from 
the  brain,  is  distributed  to  the  anterior  ])ortion  of  tlie  dige.s- 
tive  tract.  The  eyes  arc;  usually  nunuMous,  threci  or  four  jjairs 
orourring  on  tlie  anterior  ])orti()n  of  tlie  cephalothorax,  their 
arifuigement  varying  in  different  genera. 

C'oxal  glands  have  been  found  in  several  forms  in  connec- 
tion with  the  first  i)air  of  legs,  and  in  Mjigale  tliey  occur  in 
connection  with  the  third  pair.  The  reproductive  organs 
«'|"'ii  in  botli  sexes  by  a  singl"  opening  situated  near  tlie 
■interior  end  of  tlie  abdomen  between  the  .-interior  stigmata. 
'Iho  ovaries  {ov)  are  paired,  or  may  unite  to  form  a  rinLr,  and 


t 


on 


I 


462 


INVERTEBHA  TE  MORPHO LOG  Y. 


tlie  two  short  oviducts  unite  to  form  a  vagina  with  which 
may  be  associated  receptacuhi  semiuis  {rs),  though  more  usu- 
ally these  structures  open  independently  in  front  of  the 
genital  orifice  and  may  be  single,  or  paired,  or  in  some  ca.si  ,s 
even  three  in  number.  The  testes  are  cy- 
lindrical structures  whose  long,  slender,  uiJd 
frequently-contorted  vasa  deferentia  unite 
just  before  opening  to  the  exterior.  A 
remarkable  copulatory  organ  is  formed  liv 
the  terminal  joint  of  the  i)edipalp  of  the 
male  (Fig.  207),  which  bears  upon  its  inner 
surfjjce  a  process  cojitaining  a  spirally- 
coiled  tul)e.  This  tube  opens  at  the  ex- 
Fnj.  207.~PEDiPArp  ^^"^["^^^J  »/  t^^*^  process,  and  is  filled  by  tlie 
OF  Mai,i.;  SnuEu  ^pi^^er  Avith  spernnitozoa,  and  during  cojui- 
(after  ukktkau).  hitiou  is  inserted  into  the  receptacula  semi- 

uis of  the  female. 
The  males  are  usually  smaller  than  the  females,  and  tluir 
approaches  are  frequently  resisted  by  the  latter,  who  en- 
deavor to  capture  and  destroy  the  persistent  swains.  In  the 
Attidte  a  process  of  courtsiiip  has  been  observed  to  occur,  the 
male  posturing  before  the  female  and  displaying  to  their  best 
advantage  the  highly-colored  hairs  with  which  the  body  is 
covered.  The  ova  are  in  nniny  forms  (Lycosa)  attached  to 
the  under  surface  of  the  abdomen,  while  in  others  tiiev  are 
enclosed  in  a  silken  cocoon  which  may  either  be  carried 
about  by  the  female  or  suspended  in  the  webs  or  deposited  in 
protected  situations. 

Two  suborders  are  recognized,  accoi-ding  as  there  are  two 
pairs  of  lung-books  or  only  one.  The  TcfrapiicMmoui's  in- 
clude the  forms  with  two  i)airs  of  lung-books,  among  whieh 
are  the  Trap-door  Sj)iders,  Cfenizft,  already  mentioned,  and  the 
Tarantula,  Jhnjifh',  tlie  largest  of  all  the  spiders  and  reputr,^ 
to  attack  oven  small  birds.  The  Dipneumone.s  have  bin  ,t 
single  pair  of  lung.l)ooks,  the  majority  of  living  spiders  he 
longing  to  the  subonhir.  Some,  such  as  /i/>r/\vf,  Jf/ehna,  Tt'ijc- 
vnri'ii,  T/ict'idinni,  and  Seijesfria,  spin  wol)s,  while  others  c.Arh 
thoir  j)rey  by  their  rapid  movenjenta  (Lycihsti)  or  by  sudd(>iilv 
springing  upon  it  (Attufi). 


TYPE  ARACHNID  A. 


453 


with  wLich 
;h  more  usii- 
iout  of  tli(> 
1  some  ea^s(^s 
istes  are  cy- 
wleiider,  uud 
fentiu  unite 
ixterior.  A 
s  formed  by 
palp  of  tlie 
)oii  its  inner 
a  spirally- 
at  the  ex- 
died  by  the 
uriu^  cojm- 
tacula  seiai- 

!s,  and  their 
ir,  \vh(j  eii- 
ius.  lu  the 
o  ofcur,  the 
<)  their  best 
the  body  is 
attaclietl  to 
srs  they  are 
be  carried 
lepositod  in 

ere  are  two 
VKmoin's  iu- 
iioij^  which 
led,  and  tiio 
Lud  repiitr  ' 
liave  bin  ,t 
spiders  i'v 
/fluiK,  Tr(Ji'- 
'tilers  Catcii 
•}'  suddeiily 


7.  Order  Acarina. 
The  Acarina  are  for  the    most  part  small  forms,    many 
])(5iug  almost  microscopic,  while  the  largest,  the  Ticks  {Ixodes) 
do  not  when  at  tlieir  greatest  size  exceed  a  centimeter  iu 
inngth,  the  males  being  much  smaller.     Some  forms,  such  as 
<}ribates  and  Nothrus,  live  among  moss  and  in  similar  situa- 
tions, while  others,  such  as  Hydrachna  and  Afax,  are  aquatic 
Many  forms  are,  however,  parasitic   either  ujxin   plants  (^^ 
fmnychm  and  Phytoptus)  or  on  auiunils,  the  genus  Sarcoptes 
l)eiug  the  cause  of  the  disease  termed  the  Itch  in   man   the 
symptoms  being  produced  by  the  Mites  Imrrowing  beneath 
the  skin.     Other  forms  affect  various  animals  and  birds  the 
genera  Dermakichm,  AnaUjes,  etc.,  feeding  upon  the  feathers 


Fi.i.   208.-^,   Sarcoptes  scabiei ;    /?.   Demodev  phyllokles   (after  CsoK.m  fron, 

Whkiht). 

<'f  various  birds,  while  others,  such  as  Deumlex  (Fig.  208,  B), 
liv.3  1.1  the  hair-follicles  or  sebaceous  glands  of  the  skin,  pro- 
<liu'nig  acnelike  pustules.  The  larvro  of  manv  forms  whieh 
;U-H  non-parasitic  in  a.lult  life  have  a  parasitic  habit,  as  for 
iMstance  the  larva-  of  many  of  the  Water-mites  and  of  the 
Harvestmites  [TrondmUum),  while  other  forms  live  upon 
oiKunic    matter  of   various   kinds,  as  does  the   Cheese-mite, 

I  Ijt'oijlypjnis. 

A  distinguishing  characteristic  of  the  Acarina  is  tJK*  ab- 
«".'H-e  of  any  segmentation  and  the  fusion  oi  head-thorax  and 
•■^''••"""Hu  to  a  single  mass  (Fig.  208,  .1).  The  form  of  the 
■■M'!'<'iidageH  varies  greatly  in  diffi^rent  genera  according  to  the 
"^"  to  which  they  are  put.     The  ehelicera>  (Fig.  201),  Md)  are 


I 

INMM 


454 


IN  VEltTEBliA  TE  MOltPHOL  OGY. 


5  It 
;! 


frequently  chelate,  but  in  parasitic  forms  are  reduced  to 
stylets  enclosed  by  the  fused  basal  joints  of  the  pedipalps,  a 
proboscis  being  thus  produced  which  can  pierce  the  integu- 
ment and  thus  render  the  juices  of  the  host  available  as  food. 
The  pedipalps  (Alxp)  undergo  various  modifications,  being 
sometimes  long  and  limblike,  sometimes  chelate,  while  their 
basal  joints  may  or  may  not  be  fused.  The  four  pairs  of  legs 
are  generally  adapted  for  walking,  and  terminate  in  ungues  or 
bunches  of  hairs  or,  in  some  parasitic  forms,  in  suctorial 
disks,  while  in  the  Water-mites  they  are  provided  with  usually 
long  bristles  along  the  sides,  serviceable  swimming-orgaus 
being  thus  produced.  In  the  genus  Demodex  the  four  legs 
are  reduced  to  short  unjointed  structures  each  provided  with 
four  ungues,  while  in  the  Leaf-mites,  Phytoptus,  Avhicli  pro- 
duce galls  on  the  leaves  of  various  plants,  the  two  pairs  of 
posterior  limbs  are  reduced  to  wartlike  elevations  l)earing 
bristles,  the  two  anterior  pairs  being  on  the  other  hand  fiviv 
jointed. 

The  chitinous  covering  of  the  body  is  usually  thick  and 
delicately  wrinkled.  It  usually  bears  numerous  setji*  and 
occasionally  also  plates  or  lateral  prolongations,  as  in  Ori- 
bates  and  its  allies.  Dermal  glands  also  frequently  occur, 
]>roducijg  oily  tluids  and  sometimes  odoriferous  secretions. 
Spinning  glands  opening  on  the  pedi})alps  occur  in  Tetniinj- 
chns,  frequently  ])arasitic  on  the  leaves  of  the  Rose,  but  as  u 
rule  they  are  not  developed. 

A  pair  of  stigmata  (Fig.  209,  fit)  occurs  in  many  forms, 
situated  usually  near  the  coxse  of  the  last  pair  of  legs,  l)iit 
not  unfrequently  they  are  much  further  forward,  lying  near 
tiie  basal  joints  of  the  pedipal})s  or  even  of  the  chelicerji'. 
They  open  into  trachea^  which  branch  once,  bunches  of  lateral 
trachew  being  situated  at  intervals  upon  the  two  branches. 
Fre({uently,  however,  especially  in  parasitic  and  aquatic  forms, 
both  tracheiP  and  stigmata  are  wanting,  as  is  usually  also  tlu^ 
heart.  When  j)resent  ((riimd.sius,  /xodcti)  this  latter  structuiv 
is  Hunill,  with  but  a  single  pair  of  ostia,  and  is  prolonged  an- 
teriorly into  a  slender  aorta. 

The  digestive  tract  is  frecjuently  provided  with  glan<ls 
opening  into  its  anterior  portion  ati<l  supposed  to  be  salivary. 


TYPE  ARACHNID  A.  455 

The  mid-gut  usually  sends  oflf  a  number  of  c«.cal  diverticula 
which  may  branch   at   the    ends,    and    Malpighian   vessels 
some  imes  one.  sometimes  a  pair,  and  sometimes  many  are 
usually   present  while    in  addition,  in   some  forms,  a  rectal 
bladder,  similar  to  that  occurring  in  the  Araue*.  is  found 


F'G.  209.— Male  of  Oamasus  (ergipes  (after  Winkler). 


ai,  :-  anus. 

em  =  ctecal  pouches  of  iutestine, 

ffo  =  geuidil  orifice. 
Mrl  =z  cheliccm. 

mr/  =  Mjilpighiau  tubules. 
inx  =  maxilltu. 

I-IV=  limbs. 


Mxp  =  pedi  palps. 
at  =  stigma. 
sic  =  stignui-canal. 
T=:  testis. 
i  —■  tongue. 
Vd  =  vas  deferens. 


The  nervous  system,  as  might  be  suppo.sed  from  the  con 
cen  ration  of  the  body  regions,  is  composed  of  a  supraa^soph- 
«oal  syncerebrum  and  a  larger  sub,.sophagoal  ganglionic 
mass  trom  which  numerous  nerves  are  given  off.  Eyes  are 
usually  wanting,  (,r  may  be  present  in  the  form  of  one 
{Ixodes)  or  two  pairs  of  small  apparently  simple  ocelli. 

Coxal   glands  have  been  described"  nw  nP,m,M.;.w/„i  n.. 
bases  of  the  seconc" 


''AM*. 


pair  of  legs    (Oribatidte).     The 


rejjro- 


fWi' 


456 


IN  VERTEBRATE  MORPUOLOG  Y. 


.-«'« 


ductive  organs  show  much  variety  iu  their  arrangemeut, 
beiug  sometimes  paired  aud  sometimes  iiuited  to  a  siu^le 
mass.  The  single  genital  oritice  is  situated  far  forward,  iu 
some  cases  even  between  the  basal  joints  of  the  second  pair 
of  legs.  Numerous  accessory  structures  may  be  associated 
with  the  ducts,  the  receptacula  seminis  in  some  forms  open- 
ing to  the  exterior  quite  independently  of  the  oviduct,  and 
prt)trusible  organs  serving  for  copulation  in  the  male  and  lor 
ovipositiou  iu  the  female  may  occur.  The  Acariua  are  as  u 
rule  oviparous,  though  a  few  forms  are  viviparous. 

Development  of  the  Acariua. — Most  of  the  Acarina  whose  development 
has  been  traced  pass  through  a  series  of  larval  stages.  While  tiie  yomii; 
embryo  is  still  witluii  tlie  *'gg  and  sometimes  before  the  appendages  have 
developed,  a  etiticular  membrane  is  secreted  around  it  lying  between  the 
embryo  and  tlie  egg-shell.  Tiiis  is  the  (leiitoriini,  and  within  it  further 
development  proceeds.  In  those  forms  in  which  it  does  not  appear  until 
after  tiie  appendages  arc  formed  a  degeneration  of  these  structures  tai<es 
place,  and  the  egg-shell  may  also  he.  thrown  off  leaving  the  embryo  sur- 
rounded only  by  the  deutovum  {T/oiiifiidiinn).  New  appendages  now 
appear,  and  tlie  larva  hatches  out  from  the  deutovum  as  a  six-legged 
form,  sometimes  showing  traces  of  segmentation  either  iu  the  ihui'acic 
region  or  iu  the  abdomen.  After  a  certain  time  a  certain  amount  of  de- 
generation of  the  tissues  occiu's  (histolysis)  and  the  ai)pendagcs  again  dis- 
ai)I)ear,  a  chitinoiis  membrane  forming  around  the  now  almost  spherical 
body  of  the  larva.  A  regeneration  of  the  limbs  and  tissues  takes  piaco 
within  tills  larval  membrane,  and  the  nymph  is  formed,  resembling  liio 
adult  in  the  number  of  ai)pendages,  but  lacking  fully-developed  repi'u- 
ductive  organs.  A  period  of  rest,  and  histolysis  again  occurs,  accuiu- 
panied  by  the  formation  of  a  third  c'liieular  membrane  williin  which  tlic 
nymi)h  b'.^eomes  transformed  into  the  fidly-developed  and  sexually-mat inc 
adult  or  imago,  which  finally  issues  from  the  membrane. 

This  complicated  process,  it  is  needless  to  say,  has  no  phylogenetie  sig- 
nificance, the  deutovum  indeed  being  absent  in  certain  forms  {Tetnu/ij- 
chiis),  nor  does  it  st!em  likely  that  even  the  six-lcgg(!d  larva  is  anything 
but  a  secondary  stage  which  has  been  developed  within  the  group  of  ilic 
Acarina.  There  is  no  (piestion  Imt  that  the  order  represents  th**  culniin.i- 
tion  of  a  divergent  lino  of  evolution,  perhaps  fivmi  the  P.seudoscorpionida. 
and  since  the  separation  many  of  the  peculiarities  characteristic  of  tlic 
group  hav(!  been  developed. 

P/ii/loi/eiiy  of  t/ie  A/v/c/////(/«.— There  seems  little  room  for  dotibt  hut 
that  the  Scorpions  among  living  forms  represent  most  closely  the  anccsiial 
Arachnoids,  their  segmentation  being  most  perfect  and  their  ai)pend;i,u'<'s 
more  numerous  than  those  of  other  forms.     It  is  through  the  Scorpions 


TYPE  ARACHNID  A. 


457 


to  a  siuf^le 
forward,  iu 
jecoiid  pair 
associated 
orins  opeii- 
viduct,  ami 
ale  aud  lor 
la  are  as  a 


!  development 
ile  tlie  yoiiiiji 
leudiif^es  have 
C  between  llie 
liii  it  furtlici 
aiipeur  until 
riu'turos  takes 
i  embryu  hiir- 
ieiKla<j;es  now 
a  six-l('t,';,fc(i 
the  llioi'acic 
siinouut  of  (le- 
4'<'s  au'aiii  (lis- 
uost  .sijheiical 
es  takes  place 
usembliuy  liic 
eloped  repi'd- 
leeiirs,  accutu- 
liiii  wliieli  the 
xiially-niatini' 

Oogenetic  sii,'- 
rnis  {Tetraiiij- 
"A  is  aiiytliiim' 
!  jjjroiip  of  ilir 
i  the  ctiliniiiji- 
:loscorpioiii<la, 
feristie  of  tlir 

for  doubt  but 
^  the  anceslial 
ill'  appenda.Lji's 

tlie  Scorpions 


accordingly,  that  relationships  to  other  forms  must  be  looked  for,  and  a 
roruptirison  of  them  with  Limulus  reveals  similarities  of  structures  so 
numerous  and  so  detailed  that  the  conclusion  is  unavoidable  that  both  are 
to  be  traced  back  to  a  common  ancestor.  Tlius  the  cephalothoracic  ap- 
pendages in  both  are  identical  in  number,  and,  so  far  as  the  first  two  pairs 
are  concerned,  in  general  structure  also,  wliile  the  genital  oi)ercula  of  the 
Scorpions  are  comparable  in  their  relation  to  the  genital  orifices  to  the 
opcrcula  of  Llinulus,  and  the  peetines  to  the  first  pair  of  abdominal  ap- 
ix'iidages.  The  remaining  abdominal  appendages  of  Limulus,  which  are 
branchiate,  seem  at  first  sight  to  be  unrepresented,  but  the  embryo- 
logical  investigation  of  the  Scorpions  appears  to  indicate  that  they  are 
ii'presented  by  the  lung-books,  whicli  bear  no  little  resemblance  to   the 

l)ranchial    lamelhe    of    Liinulu.s,  and    the        -n, 

conversion  of  one  set  of  organs  into  the 
otlier  may  be  supposed  to  have  been  brought 
about  ))y  the  formation  behind  each  pair 
of  abdominal  appendages  of  an  invagina- 
tion, wliich,  decjpening,  has  carried  in  with 
it  the  Imiiichial  lamella',  the  original  an- 
terior surface  of  tin;  appendage  forming 
the  ventral  wall  of  the  body  beneath  the 
lung-sac,  while  the  lamella'  i)ro,jecr  into  the 
sac  for  its  ventral  surface  (Fig.  210).  In 
the  general  form  of  the  body  Limulus 
corresponds  fairly  well  with  tlu;  8corj)ions,  ^^ 

the  cei)halothoracie   regions   being  strictly  „  """"""'"^ 

comparable,  as  is   also   the   terminal  spine        '    ,"~^'^'"*^'''''' ^"'"'^ 
^vi<h  the  sting  ;   the  abdomen,  however,  in      ""^  ^^^NG-nooKS  (after  Kings- 
tlie  branchiate  form  has  a  smaller  tnimber 
"f  segments  whicli  are  all  fused,  a  ditlerence 
readily  explained  by  the  probable  derivation 

of  both  fortns  from  Enrnpterus-Wko.  ancestors  in  which  the  abdomen 
possessed  a  relatively  laig<,  number  of  distinct  segments,  and  even  showed 
indications  of  a  differentiation  into  a  pra>abdomen  and  a  postabdomcn 
(see  Fig,  198). 

In  the  internal  structure  quite  as  striking  similarities  are  to  be  found 
in  the  presence  of  an  endosternite  in  both  groups  and  of  coxal  glands  in 
connection  with  the  fifth  pair  of  appendages,  in  the  tendt  .cv  towards  the 
eencentration  of  the  postoral  ganglia,  and  in  the  invaginate'origin  of  the 
median  eyes,  to  mention  but  a  few  points. 

The  Arachnida  are  accordingly  to  be  traced  back  to  Limulus  or  Euryp. 
temsAxkQ  ancestors,  and  through  thes.,' finally  to  the  Entomostraca,  perliaps 
a  C  rustacean  ancestry  being  clearly  indicated.     As  to  the  relationslni)s  of 
tiio  .anous  orders  little  that  is  definite  can  l)e  said,  differentiations  liaving 
taken  place  along  different  lines  in  the  various  orders,  so  that  while  the 


LEY). 

1  =  indifferent  .stage. 
//  =  Limulus  stage. 
A  =  Aia(;lini(ian  staffc. 


3 


458 


INVEliTEDliA  TE  MOIWIIOLOO  Y. 


Pedipalpi  arc  more  pi'itnitive  as  regards  the  number  of  abdominal  seg- 
ments and  their  distinctness  than  tiie  Aranea",  yet  the  hitter  and  especially 
the  Tetrapneunioiies  show  a  much  more  primitive  condition  of  tlie  respira- 
tory oi'gans.  With  regard  to  tliese  organs  it  may  be  at;  d  that  the  con- 
dition in  which  they  are  represented  by  buuciies  of  un  iunched  tracheae 
is  more  primitive  than  that  in  which  they  are  branching  tubes,  the 
bunched  condition  being  probably  derived  by  a  modification  of  original 
lung- books. 

TYPE  ARACHNIDA. 

1.  Order /Scorp/omrfa. — Abdomen  segmented  and  differentiated  into  pra;- 
abdoraenand  postabdomen  ;  postabdomen  terminating  in  poison- 
spine  ;  pedipalps  chelate  ;  two  pairs  of  abdominal  api)endages  ; 
four  of  stigmata  and  lung-books.     Euscorpius,  Bathus. 

3.  Order  Pseiidoscorpioithla. — Abdomen  segmented  but  not  differentiated  ; 

no  terminal  spine  ;  pedipalps  chelate  ;  no  abdominal  appen- 
dages;  two  pairs  of  stigmata  opening  into  trachea;:  first  pair 
of  legs  adapted  for  locomotion.  CheUfei\  Obisiuvi,  Cheriiea. 
8.  vU'dei  Solifugw. — Head  separated  from  tliorax  with  thret;  segments; 
abdomen  segmented  but  undifferentiated ;  no  terminal  spiiu; ; 
pedipalps  palplike  ;  three  pairs  of  stigmata  leading  into  trachea\ 
Oaleodes,  Solpuga. 

4.  Order  Pedipalpi. — No  distinction  of  head  and  thorax  ;  abdomen  seg- 

mented, and  either  undifferentiated  or  with  three  small  segments 
terminated  by  a  multiarticulate  tlagellum  ;  pedipalps  leglike  or 
subchelate  ;  two  pairs  of  stigmata  and  lung-books  ;  first  pair  of 
legs  elongated  and  palplike.     Phryntts,  ThehjpUonus. 

5.  Order  Pltalamjlda. — Abdomen    segmented    but  undifferentiated  and 

without  appendages  or  terminal  spine  ;  pedipalps  leglike  ;  one 
pair  of  stigmata  leading  into  trachea; ;  no  spinning-glands. 
Leiohunum,  P/ialanyium,  Opilio,  Qonyleptus,  Cyphophthalmus, 
GibbocelluiH. 

6.  Order  Araiieir. — Abdomen  nnsegmonted  and  with  two  or  three  pairs  of 

rudimentary  papillalike  appendages  bearing  the  openings  of 
ducts  of  numerous  spinning-glands ;  abdomen  not  fused  with 
eephalothorax  ;  pedipalps  long  and  palplike  or  leglike. 

1.  Suborder  Tetrapneumonen.  —  With  four   stigmata  opening  into 

sacs  containing  lung-books.     Mygale,  Cteniza. 

2.  Suborder  Dipnenmones. — With  four  or  three  stigmata,  the  anterior 

pair  opening  into  sacs  with  lung-books,  the  posterior  one  or 
two  with  trachea?.  Epeira,  Agelena,  Tegenaria,  Tlierkliniit, 
Segestria,  Attus,  Lycosa. 

7.  Order  Acarina.  —  Abdomen  unsegmented,    without  appendages,  ami 

fused  with  the  eephalothorax ;  pedipalps  sometimes  long  uml 
leglike,  sometimes  chelate ;   stigmata  wanting  or  present  as  a 


TYPE  AUACUNIDA. 


ilorainal  seg- 
nd  especially 
[  the  respira- 
thiit  the  con- 
;he(l  tracheie 
;  tubes,  the 
I  of  original 


469 


single  pair  leading  into  tracheue ;  many  forms  parasitic  •  fre- 
quently with  complicated  metamorplioses.  ' 

Nonparasitic,  or  ])arasitic  only  in  larval  stage  ;  terrestrial  Ori- 
Oates,  JVothntfi,  TrombkUum. 

A(iuatic.     HydracluM,  A  tax. 

Living  on  organic  matter.     Ti/rof/li/p/nis. 

Parasitic  on  animals.  Deinodex,  Sarcoptes,  Dermaleiclnts  Anal- 
(jes,  Oamasus,  Ixodes. 

Parasitic  on  plants.     Tetranyehus,  Phytoptus. 


cd  into  praa- 

ingin  poison- 
api)endages ; 
thus. 

tTerentiated  ; 
iiinal  appon- 
aj :  first  pair 
<,  Chernes. 
e  segments ; 
minal  spine ; 
into  trachea\ 

bdomcn  sog- 
iiall  segments 
ps  leglike  or 
;  first  pair  of 
us. 

Bntiated  and 

leglike  ;  one 

ining-glands. 

lophthalmus, 

;hree  pairs  of 
openings  of 
Dt  fused  with 
ike. 
opening  into 

,  the  anterior 
terior  one  or 
,  Theridiniii, 

3ndages,  anil 
3CS  long  uml 
present  as  a 


LITERATURE. 

GENEIIAL. 

H.  Grenacher.   Unterauchunge7i  iiber  das  Sehorgan  der  Arthropoden.  GC.ttingen, 
^'  ^uT^T.xi'"'''^''"  ""^  ^'■"'^'   ''^-    ^'"^'■^^'•'^  J"""-"-  Microscop.  Sci- 

vIKC,    A-XI,    loo  J.. 

J.  Macleod      liecherckes  sur  la  structure  el  la  signification  de  I'appareil  respira. 
toire  des  Amchnides.     Archives  cle  Biologic  v  1884 

^'  'wTc^rix^tso?''"''^'"*'''  '^'''  ^'•"'''"^"^^«'    '^'''"^'^^  a-  ^-  Zoolog.  Inst. 

J.  S.  Kingsley.  The  Embryology  of  Limulus.  Part  II.  Journ.  of  Mor- 
phology, VIII,  1893.  ^^^*^* 

BCOIJPIONIDA. 

1.    Dufour.    Ilistoire   cmatomique   et  physiologique  des   Scorpions.    Memoirs 

Aciid.  Sciences.     Paris,  xiv,  1856.  ^tuiuiis 

E.  K^I;anke8ter.     On  tkeCoxal  Glands  of  Scorvio,  etc.,  and  the  Brick-red 

^^l^ndsoJUmulus.     Proceedings  of  the  Royal  Society,  xxxi v.  1884. 
G.  H  Parker.     Ike  Eyes  m  Scorpions.     B.llctiu  of  the  Museum  of  Compar- 
ative Zoology,  XIII,  1879.  v^umpar- 

W,  Patten.  The  Origin  of  Vertebrates  from  Arachnoids.  Q.mrterly  Journal 
of  Microscop.  Science,  XXXI,  1890.  J  -Jouinai 

M.  Laurie.  The  Embryology  of  a  Scorpion  {Euscorpius  itaiicus).  Q.mrterlv 
Jouiu.  Microscop.  Science,  xxxi,  1890.  V£<"iutriy 

rSEUDOSCOKPIONIDA. 

A.  Croneberg.  Beitragzur  Kennt7riss  des  Banes  der  Pseudoscorpione.  Bulletin 
hoc.  Imp.  Nuturalistes  Moscou,  ii,  1888.  -tsu'ittm 

SOLIFUG/E. 

1.  Dufour.  Anatomic,  physiologic,  et  histoire  naturelle  des  Galeodes.  Me- 
moires  Acad.  Sciences,  Paris,  xvii,  1858. 

niALANGIDA. 

^  wisf  ■  1  T7'  '"'  t"''"""''  '^"'  ^^^^^^^^'mlen-  Zeitschrift  fur 
\\issensch.  Zool.,  XXX VI,  188:2. 


i 


'SUM.. 


%* 


^ 


w 


IMAGE  EVALUATION 
TEST  TARGET  (MT-3) 


/ 


O 


1.0 


I.I 


1.25 


■  45 
110 


^  1^    12.2 


IT  1^4 

1^  IIIIIM 


18 


U_  IIIIII.6 


6' 


<P^ 


7 


"^ 


/. 


s^.v      W 


"# 


PhotDgraphic 

Sciences 
Corporation 


33  WIST  MAIN  STRUT 
WIASTER.N.Y.  14.    0 


.^ 


^ 


r^ 


..#^> 


%^ 


n\ 


■li^ 


^ 


6^ 


^Lfc^'^ 


C/j 


^ 


mm 


460 


INVERTEBRATE  MORPHOLOGY. 


C.  M.  Weed.     A  Descriptive  Catalogue  of  the  Harvest- spiders  (Phalangiida)  of 
Ohio.     Proceedings  United  States  National  Museum,  xvi,  1893. 


2;-« 


ARANEiE. 

E.  Zeyserling.     Die  Spinnen  Amerikas.    Nttruberg,  1880-91. 

G.  W.  and  E.  0.  Peckham.     North  American  Spiders  'of  the  Family  Attidm. 

Transactions  of  the  Wisconsin  Acad.  Sciences,  1888. 
H.  C.  McCook.     American  Spiders  and  their  Spinning  Work.    Philadelpliia 

1889-90.  ' 

J.  H.  Emerton.    Papers  in  tbn  Transactions  of  the  Connecticut  Academy  vii 

1889,  and  viii,  1891. 

0.  Marx.     Papers  in  tlie  Proceedings  of  the  Entomological  Society  of  Wasli- 
iugtou,  1891.  and  iu  the  Proceedings  of  the  U.  S.  National  Museum  xii 

1890.  '       ' 

W.  Sohimkewitsoh.     Etude  sur  Vanatomie  de  I'Epeire.    Annales  des  Science* 

Naturelles,  6meser.,  xvii,  1884. 
Ph.  Bertkau.     Ueber  den   Verdauungsapparat  bei  Spinnen.    Archiv.  fUr  mi- 

krosliop.  Anatomie,  xxiv,  1885. 
Bcitrage  zur  Kenntniss  der  Sinnesorgane  bei  Spinnen.     I.  Die  Augai. 

Archiv  fUr  miliroskop.  Anatomie,  xxvii,  1886. 
£.  L.  Mark.     Simple  Eyes  in  Arthropods.    Bulletin  Museum  of  Comparative 

Zoology,  XIII,  1887. 
A.    T.   Brace.     Observations  on   the  Embryology   of  Insects  and  Arachnids 

Baltimore,  1887. 

ACARINA. 

0.  Haller.     Zur  Kenntniss  der  Tyroglyphen  und  Verwandten.     Zeitscbr.  fiir 

wissensch.  Zoologie,  xxxiv,  1880. 
H.  Henkingr.     Beitrdge  zur  Anatomie,  Entwicklungngeschichte  and  Biologic  roii 

Troinbidium  fuligiiiohum.     Zeitschr.  fUr  wissensch.   Zoologie    xxxvii 

1882.  "  '       ■ 

A.  D.  Michael.     British  Oribatidm.     Lond(;n,  1984. 
A.  Nalepa.     Anatomie  der  Phytopten.     Sitzungsber.  Akad.  wissoiisch    Witii 

xcv,  1887. 

W.  Winkler.     Das  Ilerz  der  Acarinen  nebst  vergleichenden  Bemerkungen  uber 
das  Ilerz  der  Phalangiden  und  Chernetiden.     Arbeiten  a.  d.  zool    Ins 
Wien,  VII.  1888. 

Anatomie  der  Oamasiden.     Arbeiten  a.  d.  zoolog.   Inst.   Wien    vir 

1888. 


APPENDIX  TO  THE    \UACIINIDA. 

There  are  three  orders  which  show  a  certain  amount  of 
affinity  to  tlie  Ar-ichuida,  but  which  are  not  so  ch).sely  reiatid 
as  to  warrant  the  actual  association  of  them  with  the  orders 
which  have   heen  assigned  to  that  tvpe.     They  will  be  de- 


lih 


TYPE  ARACHNID  A. 


461 


Zeltscbr.  fiir 


L'nsch.  Willi, 


i 


scribed  here,  and  are  the  orders  of  the  Fentastomidce,  the 
Pycnogonida,  and  the  Tardigrada, 

Order  PentastouidsB. 

The  PentastomidsB  are  all  parasitic,  living  in  the  adult 
stage  in  the  lungs  or  nasal  cavities  of  various  animals,  one 
species,  PentoMomum  tcenioides,  occurring  in  the  nasal  cavities 
or  sinuses  of  dogs  and  Avolves,  VAhile  several  species  have  been 
found  in  the  lungs  of  different  sptcies  of  snakes  (Fig.  211). 
They  are  all  elongated  wormlike  forms,  some- 
times slightly  flattened  and  usually  distinctly 
aunulated,  the  annuli,  however,  not  repre- 
senting a  metamerism.  The  anterior  end  of 
the  body  is  rounded  and  bears  on  the  ventral 
surface  the  mouth,  upon  each  side  of  Avhicli 
is  situated  a  pair  of  strongly-recurved  hooks 
{h)  supplied  with  special  muscles  and  serving 
for  the  attachment  of  the  animal  to  the  tissues 
of  the  host.  With  the  exception  of  these 
hooks  no  appendages  are  present. 

The  body  is  covered  by  a  cuticle  secreter" 
by  the  ectodermal   cells   (hypodormis),    be- 
neath which  lies  a  layer  of  circular  muscle- 
libres,  and    beneath  these   again    a   lnyex  of 
longitudinal  muscles.     The  coelom  is  ample 
and    is    traversed    by  dorso-ventral    muscle- 
bands,  which  divide   it   into  a  central  com- 
partment containing  the  various  organs,  sus- 
). ended  by  mesenteries,  and  two  lateral  ones.     ;„„,^  Femalr .after 
lliere  is  no  heart  or  circulatory  apparatus,    spkncbr). 
and  trachefP  or  othor  respiratory  organs  are    '*  "^  Jiooks. 
also  wanting.  ^"  =  *^«"'^'''  "••^^'■«- 

The  digestive  tract  is  a  straight  tube  extending  through 
tlie  body  from  the  mouth  to  the  terminal  anus,  giving  off  uo 
lateral  diverticula  throughout  its  course.  The  nervous  sys- 
tem (Fig.  212,  wo)  consists  of  a  ganglionic  mass  lying  below 
tlib  (imophagus,  a  c<)m})aratively  small  commissural  ring 
passuig  round  that  portion   of  tlie  digestive   tract,  without, 


Fm.    %n.  —  Penta- 
Htomu7,i  teretiusru- 


ISWu. 


462 


INVERTEBRATE  MORPHOLOGY. 


however,  possessing  any  ganglionic  enlargement  which  can 
be  termed  a  cerebrum.  Various  nerves  are  given  off  from 
the  mass,  two  of  which  extend  backwards  throughout  nearly 
the  entire  length  of  the  body.  The  only  sense-organs  pres- 
ent are  a  number  of  small  papillee  on  the  anterior  portion  of 
the  body,  which  are  probably  tactile  in  function. 

Glandular  organs  are  highly  developed.  Scattered  over 
the  surface  of  the  body  are  numerous  flask-sliaped  glands 
apparently  ectodermal  in  origin,  while  lying  in  the  coelom  on 
each  side  of  the  mid-gut  and  extending  back  almost  to  the 
posterior  ena  of  the  body  are  two  long  c^cal  tubes,  a  glan- 
dular structure  being  also  connected  with  them  anteriorly 
These  glands  open  in  the  vicinity  of  the  hooks  and  have 
hence  been  termed  the  hook-glands  (Fig.  211,  hg),  and  it  has 
been  suggested  that  they  secrete  a  fluid  which  serves  to  keep 
the  blood  which  the  parasite  ingests  from  coagulating,  being 
thus  similar  to  the  glands  in  the  pharynx  of  the  Leeches 


Fig.  212.— Diagham  op  Structuhe  op  Femat,e  Pentnstomum  (after  Spenkcb). 
go  =  genital  orifice.  od  =  oviduct. 

hff  =  hoolc-glaiid.  ov  =  ovury. 

I  =  intesliue.  j-g  =  seminal  receptacle. 

ng  =  nerve-ganglion.  ut  =  uterus. 

which  serve  the  same  purpose.  Unless  the  eciodermal  glands 
are  excretory,  no  special  organs  for  the  carrying  on  of  that 
function  occur. 

The  Pentastoniidre  are  bisexual,  the  mule  being  smaller 
than  the  female,  aud  recognizable  l)y  the  situation  of  the  geni- 
tal orifice  (Fig.  211,  70),  which  is  near  the  anterior  end  of  the 
body,  wljilo  in  t\w  female  it  is  near  the  posterior  end.  The 
ovary  and  testis  are  both  uii])aired  organs  situated  beneath 
the  dorsal  surface  of  the  body  and  extending  almost  its  eutiro 
length.  Anteriorly  a  pair  of  oviducts  (Fig,  212,  <)<i)  arise 
from  the  extremity  of  the  ovary  (pv)  and  pass  downwards  and 


TYPE  ARACHNIDA. 


463 


ter  Spbnbcr). 


forwards  towards  the  ventral  surface,  on  nearing  which  they 
uuite  to  form  a  long  coiled  tube,  the  uterus  {ut),  which  passes 
backwards  to  the  genii.:!  orifice,  and  just  where  the  two  ducts 
uuite  they  have  opening  into  them  a  pair  of  pyriform  seminal 
receptacles  (rs).  The  vasa  deferentia  are  also  paired,  and 
arise  at  the  anterior  end  of  the  testis,  passing  ventrally 
towards  the  genital  pore,  uniting  before  they  reach  it  and 
dilating  to  form  a  complicated  intromitjent  organ,  from  which 
two  tubes  with  muscular  walls  and  containing  spermatozoa 
project  backwards  and  serve  as  ejaculatory  ducts  for  the  ex- 
pulsiou  of  the  spermatozoa  through  the  intromittent  organ. 
The  only  genus  belonging  to  the  order  is  Pentastomum.  ' 

Development  of  the  Fenta-stomirice. -Dining  the  life-history  of  a  Pen- 
tastomum  it  passes  through  a  marked  metamorphosis  associated  with  a 
change  of  hosts,  recalling  what  occurs  in  the  CestwJa.     The  ova  are  passed 
to  the  exterior  with  the  excreta  of  the  host,  or,  in  the  case  of  the  dog 
with  the  mucous  discharge  from  the  nasal  passages,  and  the  embryo  which 
hatciies  out  is  a  decidedly  Mitelikc  tovv^    oossessing,  however,  only  two 
pairs  of  legs  terminating  in  ungues.    No  other  appendages  are  present 
but  Che  embryo  is  provided  anteriorly  witii  a  boring  apparatus     If  this 
arva  of  P.  t,xnioide,,  the  parasite  of  the  dog,  succeeds  in  gaining  entrance 
to  the  digestive  tract  of  a  rabbit  or  cat,  for  instance,  it  bores  through  the 
wall  of  the  intestine  and,  reaching  the  liver,  encysts  itself.     Within  the 
cyst  It  undergoes  several  moults,  finally  assuming  a  condition  similar  to 
the  adult  except  that  each  annulus  bears  a  circle  of  hooks.     Leaving  the 
cyst,  then,  it  wanders  through  the  tissues  of  the  host,  and  if  while  it  is  in 
tins  condition  the  host  is  eaten  by  a  dog,  it  adheres  to  the  mucous  mem- 
hrane  of  the  mouth  of  the  latter,  and  makes  its  way  into  the  nasal  p,u«sages 
there  moulting  again,  losing  tiio  ring  of  hooks  and  assuming  the  adult  form' 

1  he  principal  rea.son  for  mx>\Mmng  Pentastomum  to  be  related  to  the 
Arachnids  is  the  occurrence  of  the  four-legged  larva,  which  resembles  so 
tar  as  Its  external  form  is  concerned,  a  Mite.  The  internal  structure  is 
\ my  different,  however,  although  corfain  Arachni.l  features  are  indicated  ■ 
I'ut  It  IS  evident  that  the.se  forms  must  have  undergcu.e  an  enormous  de- 
l-amire  from  the  ancestral  form  during  which  the  remaikal)le  life-historv 
an.l  peculiar  structure  have  been  acquired.  The  parasitic  habits  of  many 
liu-s.  and  the  general  similarity  of  tiie  body  form  of  Demmlex  to  that  of 
I'Htastom.im,  suggest  the  Mites  as  the  ancestors  of  the  latter,  a  theory 
wlacii  IS  as  plausible  as  any  other  which  can  at  present  be  suggested. 

Order  Pycnogonida. 
The  Pycnogonida  are  exclusively  marine  in  habitat,  and 
vary  considerably  in  size,  the  smaller  forms,  such  as  Tamjsty. 


It 

Ml' 


«... 


'X  i 


464 


INVERTEBRATE  MORPHOLOGY. 


lum,  being  only  about  a  millimetre  in  breadth,  while  the 
purple  Fhoxichilidium  measures  over  three  millimetres  from 
tip  to  tip  of  the  legs,  and  the  deep-sea  form  CoUossendeis  has 
a  span  of  over  sixty  centimetres.  The  body  proper  is  compar- 
atively small,  the  four  pairs  of  long  legs  which  arise  from  the 
thorax  being  exceedingly  conspicuous,  a  feature  which  has 


Fig.  213. — Phoxichilidivm  mnxillare  (after  Morgan). 

suggested  the  term  Fanfopoda  sometimes  applied  to  the 
group.  An'oriorly  there  is  a  ivell-marked  proboscis  carrying:; 
the  mouth  at  its  anterior  end,  and  at  the  base  of  this  there 
arise  the  cheliceriB,  which  are  rather  short  chelate  limbs. 
The  next  segment  of  the  body  succeeding  that  which  bears 
the  cheliceru}  bears  upon  its  dorsal  surface  the  eyes,  and  may 
be  regarded  as  a  fusion  of  three  segments  since  it  bears  three 
pairs  of  appendages.     The  most  anterior  of  these  are  slender 


' 


TYPE  ARACUNIDA. 


465 


jointed  palps;  the  econd  pair,  wautiug  in  the  females  of 
some  species,  but  always  present  in  the  males,  arise  from  the 
ventral  surface  of  the  segment,  and  are  curved  jointed  struc- 
tures serving  to  carry  the  ova ;  while  the  third  pair  are  ex 
ceeding  long  jointed  walking-legs.  The  next  three  segments 
nlso  bear  long  walking-legs,  the  last  one  having  attached  to 
it  the  usually  unsegmented  rudimentary  abdomen. 

The  body  and  the  appendages  are  encased  iii  a  well-de- 
veloped chitinous  cuticle,  and  there  are  no  indications  of 
special  respiratory  organs.  The  heart  lies  immediately  be- 
neath the  dorsal  integument  and  is  a  simple  tubular  organ 
with  from  two  to  three  pairs  of  ostia. 

The  portion  of  the  digestive  tract  which  lies  within  the 
proboscis  is   lined  with   chitin  and    opens    behind   into   an 
elongated  mid-gut,  from  which  long  diverticula  extend  out  into 
the  chehceraa  and    the  proboscis  and  into  the  walking-legs 
sometimes  reaching  even  into  the  terminal  joints  of  the  latter' 
A  short  hind-gut  leads  to  the  anus  at  the  tip  of  the  abdomen 
The  nervous  system  consists  of  a  supracesophageal  gan- 
glionic mass,  from  which  arise  the  optic  nerves  and  those  for 
the  chehcerae,  as  well  as  certain  nerves  passing  to  the  pro- 
boscis.    Connected  with  this  brain  by  circumoesophageal  com- 
missures IS  a  ventral  chain  consisting  of  five  pairs  of  ganglia 
the  first  pair  of  which  is  really  formed  by  the  fusion  of  two 
pairs,  distinct  in  the  embryo,  and  innervates  the  palps  and  the 
oyigei-ous  legs,  while  the  four  pairs  of  walking-legs  are  sup- 
phed  by  the  remaining  four  pairs.     Finally  one  or  two  small 
guugha  also  occur,  innervating  the  abdomen.     The  eyes  are 
imir  in  number,  situated  at   equal   intervals   upon  a   small 
(lomelike  elevation  on  the  dorsum  of  the  first  thoracic  seg- 
ment, which,  it  is  to  be  remembered,  is  compound.     Each  eye 
IS  covered  by  cuticle,  sometimes  thickened  so  as  to  form  a 
lens,  below  which  is  a  layer  of  cells  forming  the  corneal  or 
cuticular  hypodermis.     Below  this  comes  a  thick  layer  com- 
posed ot  retinal  elements  with  nuclei  in  their  outer  portions 
and  rodhke  bodies  towards  the  inner  ends  where  they  rest 
iil)on  a  layer  of  pigment.  , 

Tlim'  eyes  recall  the  poslbacillar  eyes  of  tl.o  Arachni.ls  by  their  struct- 
me,  but  show  one  renmrkable  peculiarity,  i.e.,  a  distinctly  bilateral  ar- 


^mmmm 


466 


IN  VERTEBRA  TE  MORPHOLOO  T. 


P? 


,««•  nil 


rangement  both  of  the  corneal  hypodermis  and  of  the  retinal  elements,  a 
distinct  raphe  being  observable  upon  the  inner  surface  of  the  eye,  the  reti- 
nal elements  being  arranged  on  either  side  of  it.  Such  a  condition  as  this 
cannot  readily  be  explained  by  a  simple  unilateral  invereion  such  as  was 
described  as  probably  occurring  in  Arachnidan  eyes;  it  suggests  rather  an 
invereion  of  two  sides  of  a  primitive  optic  cup,  the  posterior  wall  at  tlio 
same  time  forming  the  pigmented  layer  of  the  eye.  "Whether  the  Arachnid 
eye  is  not  also  traceable  to  such  an  arrangement,  all  traces  of  the  original 
raphe  being  lost,  is  a  question,  though  at  present  it  seems  more  probable 
that  it  has  been  produced  by  a  suppression  of  the  inversion  of  one  side  of 
the  cup. 

Glands,  occurriag  in  the  palps  and  ovigerous  legs,  have 
been  regarded  as  excretory  in  function,  but  no  Malpighiuu 
tubules  or  coxal  glands  seem  to  exist,  though  an  homologj-  of 
the  excretory  glands  just  mentioned  and  of  glands  occurring  iu 
the  walkiug-legs  of  the  males  with  the  latter  is  not  impossible. 
The  Pycnogonids  are  bisexual,  the  reproductive  organs  lying 
in  the  thorax  and  sending  out  branches  into  the  walking-legs, 
on  the  fourth  joints  of  one  or  more  of  which  they  open.  As 
already  stated,  the  male  carries  the  eggs  upon  his  ovigerous 
legs,  fastening  them  as  they  are  extruded  by  the  female  by 
means  of  the  excretion  of  the  gJauds  occurring  upon  the 
walking-legs. 

Development  and  Affinities  of  the  Pycnogonida. — The  young  Pyciio- 
gonid  leaves  the  egg  as  a  six-limbed  embryo,  which  recalls,  in  a  general  way. 
the  nauplius  of  the  Crustacea,  and  indeed  has  suggested  a  derivation  of 
the  Pycnogonids  from  that  group.  The  resemblance  is,  however,  but 
superficial,  important  differences  being  found  in  the  structure  of  the  eyes 
and  in  tiie  absence  of  an  anus,  to  say  nothing  concerning  the  details  of  the 
early  development.  On  the  other  hand  these  last,  as  well  as  the  structure 
of  the  eyes,  recall  the  Arachnids,  and  it  seems  most  probable  that  the 
Pycnogonids  are  to  be  regarded  as  having  descended  from  ancestors  wIiIlU 
might  have  been  included  in  the  type  Arachnida. 


Order  Tardigrada. 

The  Tardigrada  are  small  forms  not  exceeding  a  milli- 
metre in  length,  with  an  uusegmented  body  provided  with 
four  pairs  of  short  conical  appeudages  tipped  with  claws,  tiie 
last  pair  being  situated  at  the  posterior  extremitj-  of  the  body. 
The  body  is  covered  by  a  cuticle  secreted  bj'  the  subjacent 
hypodermis,  below  which  and  traversing  the  coelom  is  a  well- 


TYPE  ARACHNID  A. 


467 


developed   system  of  muscle-bands.     There   are   no   special 

organs  either  for  respiration  or  circulation. 

The  mouth  (Fig.  214,  m),  surrounded  by  papilla,  lies  at  the 

anterior  extremity  of   the   body,   and   leads   into  a   tubular 

mouth-cavity  containing,  imbedded  in 

its  walls,  a  pair  of  chitinous  or  partly 

calcareous   teeth,  and   receiving  the 

ducts  of  two  glands  {sg)  which  have 

been  regarded  as  salivary  or  perhaps 

poisonous  in  function.      Behind,  this 

cavity  opens  into  a  muscular  pharynx 

which  is  connected  by  a  short  a3so- 

phagus  with  the  mid-gut  (s).     At  the 

junction  of  this  with  the  rectum  or 

hind-gut  is  a  pair  of  cfiecal  diverticula 

{mg\    possibly    Malpighian   tubules, 

and  into  the  hind-gut  there  also  open 

the  ducts  of  the  reproductive  organs, 

the  hind-gut  thus  serving  as  a  cloaca. 
It  opens  on  the  ventral  surface  of  the 
body  a  short  distance  from  the  pos- 
terior  extremity  and  therefore  in  front 
of  the  last  pair  of  appendages. 

The  nervous  system  consists  of  a 
supracfisophageal  ganglion  (ce)  united 
with  a  chain  of  four  pairs  of  ventral 
ganglia.  No  special  sense-organs  occur 
except  two  eyes  situated  at  the  sides 
of  the  head.  The  sexes  are  distinct, 
the  reproductive  organ  being  un- 
paired and  opening  into  the  cloaca, 
into  which  opens  also  in  both  sexes 
au  unpaired  accessory  gland. 

The  Tardigrada  occur  in  water  usually,  especially  in  such 
locations  as  the  gutters  on  the  roofs  of  houses,  though  some- 
txines  found  also  among  moss.  The  group  contains  but  a 
small  number  of  genera,  of  which  Macrohiotus  is  perhaps  the 
most  common. 


Fig.  214.  —  Diagram  op 
Stkucture  op  Macrobiotua 
megalonyx  (after  von  Erlan- 
oek). 

an  —  iiuus. 

ce  =  cerebral  gauglion. 
e^—  e*  =:  appendages. 
h  =  bindgut. 
m  =  moutb. 
mg  =  mid-gut  diverticula. 
oc  =  eyv. 
a  =  midgut. 
iff  =  salivary  (?)  glands. 
so  =  suboesopbageal  gan- 
glia. 


468 


INVERTEBRATE  MORPITOLOOT. 


«3  lis 
2  "5 


Affinities  of  tlie  Tardigrada.—ThQ  presence  of  four  pairs  of  limbs  has 
usually  been  regarded  as  pvMnting  to  a  relationship  of  these  forms  with  tho 
Acarina,  but  the  absence  of  all  mouth-appendages,  the  structure  of  the 
legs,  and  the  position  of  the  last  pair  with  regard  to  the  anal  opening,  not 
to  mention  the  peculiarities  of  the  internal  organization,  are  opposed  to 
any  close  relationship  with  the  Arachnida.  The  Tardigrada  must  be  con- 
sidered as  holding  an  independent  position,  without  distinct  indications  of 
relationship  with  any  of  the  types,  until  further  information  as  to  their 
primitive  relationships  has  been  secured.  In  addition  the  embryological 
history,  which  has  recently  been  worked  out,  furnishes  no  evidence  in  favor 
of  Arachnidan  afiflnities,  and  it  seems  quite  probable  that  the  Tardigrades 
should  be  removed  entirely  from  among  the  Arachnida  and  possibly 
associated  with  such  forms  as  the  Echinodera. 

LITERATURE. 

PKNTASTOMIDA. 

B.  Leuckart.    Bau  und  Entwicklungsgeschichte  der  Pentastomen.     Leipzig  uud 

Heidelberg,  1860. 

C.  W.  Stiles.     Bau  und  EntwicklungsgescMchte  von  Pentastomum  pi'ohosddeum 

und  P.  subcylindrictim.    Zeitschr.  flir  wissensch.  Zoologie,  Lii,  1891. 
A.  B.  Spencer.     17ie  Anatomy  of  Pentastomum  ieretiusculum  {Baird).    Quar- 
terly Journal  of  Microscop.  Science,  xxxiv,  1892. 

PYCNOGONIDA. 

I.  B.  Wilson.  The  Pycnogonida  of  Neto  England  and  Adjacent  Waters.  Re- 
port of  the  U.  S.  Commissioner  of  Fish  and  Fisheries  for  1878.  Wash- 
ington, 1880. 

A.  Dohrn.  Die  Pantopoden  des  Oolfes  ton  Ncapel.  Fauna  und  Flora  des 
Golfes  von  Neapel.     Monographic,  in,  1881. 

P.  P.  C.  Hoek.  Report  on  the  Pycnogonida.  Scientific  Results  of  the  Voyage 
of  H.M.S.  Challenger.     Zoology,  iii,  1881. 

T.  H.  Morgan.  A  Contribution  to  the  Embryology  and  Phytogeny  of  the  Pycno 
gonids.  Studies  for  the  Biol.  Laboratory,  Johns  Hopkins  University,  v, 
J891. 

TAIIDIGKADA. 

X.  Plate.    Beitrdge  zur  Naturgeschichte  der  Tardigraden.    Zoolog.  JahrbUcher, 

Anatom.  Abtheilung,  iii,  1888. 
E.  von  Erlanger.    Beitrdge  zur  MorpJiologie  der   Tardigraden.     Morpholog. 

Juhrbuch,  xxii.  1895. 


TYPE  TB ACHE  AT  A, 


469 


CHAPTER  XV. 


TYPE  TRACHEATA. 

The  Tracheata  are,  like  the  Araclmida,  essentially  terres- 
trial forms,  for,  though  a  few  Insects  have  adapted  themselves 
to  an  aquatic  mode  of  life,  they  are  nevertheless  air-breathers, 
living  either  at  the  surface  of  the  water  or  coming  to  the  sur- 
face from  time  to  time  to  renew  the  air  contained  in  the 
tracheae  which  ramify  through  the  body  and  serve  as  respira- 
tory organs.  However,  a  few  Insect-larvse  have  acquired  the 
power  of  extracting  oxygen  from  the  water  by  branchia-like 
processes  of  the  body,  but,  even  in  these  cases,  trachero  form 
the  organs  by  which  the  respiration  is  carried  on,  the  branchi^ 
being  richly  supplied  with  them. 

The  body  is  distinctly  segmented  (except  in  Peripahis,) 
and  is  covered  by  a  chitinous  cuticle  secreted  by  the  ecto- 
dermal cells,  which  constitute  the  so-called  hypodermis.  The 
appendages  are  usually  uniramous,  and  with  few  exceptions 
{Peripatus)  are  jointed.  The  anterior  pair  in  all  cases  are 
more  or  less  elongated  multiarticulate  structures  provided 
with  sense-hairs,  and  are  situated  prajorallv,  while  of  the 
remaining  pairs,  varying  in  number  in  different  groups,  the 
most  anterior  pair  is  specialized  to  serve  as  mandibles,  while 
the  succeeding  one  or  two  pairs  usually  form  maxillte.  Numer- 
ous glands  of  varying  function  are  developed  in  the  hypo- 
dermis, the  most  interesting  of  which  are  the  crural  glands, 
well  developed  in  Peripatus,  and  represented  more  or  less 
perfectly  in  certain  other  forms.  In  addition  to  these,  glands 
which  secrete  an  acrid  or  offensive  fluid  {repugnatoricd  glo.nds) 
are  frequently  present,  as  well  as  others  which  secrete  waxy 
substances,  or  even  in  some  cases  silk. 

The  coelom  except  in  Peripatus  is  lacunar  throughout,  pos- 
sessing no  definite  walls,  and  is  traversed  in  various  directions 
by  muscles,  serving  to  flex  or  extend  the  body  and  to  move 


i» 


» 

IN»' 


i^«p«i«1 


470 


INVERTEBRA TE  MORPHOLOQ  Y. 


«£  llM 


I       '} 


the  appendages.    A  marked  difference  between  the  Tracheata. 
and   the   Arachnida  is   the   universal   absence   of  an  endo- 
sternite,  a  structure  of  considerable  phylogenetic  significanco 
in   the  latter  group.     A  heai't  is  invariably   present,   lying 
above  the  intestine,  and  situated  in  a  pericardial  sinus  incom- 
pletely partitioned  off.     In  the  major.ty  of  forms  the  parti- 
tion is  composed  of  a  varying  number  of  triangular  muscles, 
the  alar  muscles,  which  are  attached  by  their  bases  to  the 
walls  of  the  heart,  and   by  their  apices   to  the  body-wall. 
While  at  rest  they  are  somewhat  vaulted,  the  convexity  being 
dorsal,  and  on  contraction  flatten  down,  thus  enlarging  the 
sinus  and  causing  a  flow  of  blood  into  it.     The  heart  (Fig. 
227,  h)  is  elongated  and  imperfectly  divided  into  a  series  of 
chambers,  separated  by  pairs  of  valves  which  allow  the  blood 
to  flow  from  behind  forwards  but  not  in  the  reverse  direction, 
the  heart  being  closed  behind.      Ostia  are  present  in  the 
lateral  walls  to  allow  of  the  entrance  of  blood  into  the  heart- 
chambers,  whence  it  is  propelled  through  very  short  arteries 
which  open  widely  into  the  lacunar  spaces  of  the  ccelom.     In 
many  forms  a  central  sinus  surrounds  the  ventral  ganglionic 
nerve-chain,  the  blood  flowing  in  it  from  before  backwards, 
but  with  this  exception  definite  vessels  are  wanting.     This  is 
compensated  for  by  the  rich  branching  of  the  tracheae,  which, 
as  stated,  serve  as  respiratory  organs  and  convey  air  to  all 
parts  of  the  body ;  the  air  is  in  fact  brought  directly  to  the 
tissues,  instead  of  being  carried  to  them  by  the  blood  from 
limited  portions  of  the  surface  of  the  body.     The   bbod  is 
usually  colorless,  but  in  some  cases  is  of  a  bright  yellow  or 
green  color,  owing  to  pigment  contained  in  the  plasma,  and  it 
contains  in  all  cases  colorless  amceboid  corpuscles. 

The  tracheae  (Fig.  215,  tr)  communicate  with  the  exterior 
along  the  sides  of  the  body  by  a  varying  number  of  pairs  of 
stigmata  {st),  and  may  either  consist  of  bunches  of  unbranched 
tubes  connected  with  each  stigma,  or  of  a  number  of  richly- 
branching  tubes,  each  one  arising  from  a  separate  stigma  and 
anastomosing  in  some  cases  through  some  of  its  branches 
with  the  tubes  from  other  stigmata.  Each  stigma  is  usually 
provided  with  an  apparatus  by  which  it  may  be  closed,  ami 
in  the  Insects  the  air  is  expired  from  the  tracheae  by  the  ecu- 


isS' 


TYPE  TRACHEATA.  471 

traction  of  certaiu  dorso-ventral  muscles  of  the  abdomen 
which  cause  a  compression  of  the  organs  in  that  region  of  the 
body  inspiratioL  following  on  their  relaxation  and  the  conso- 
quent  re-expansion  of  the  abdomen.  In  structure  the  trachea 
are  simply  to  be  regarded  us  invaginations  of  the  body-wall 
aud  consist  of  a  single  layer  of  cells  continuous  with  the  hypo! 
dermis  of  the  body,  lined  within  ^^ 

—that  is  to  say,  on  the  surface 
with  which  the  air  is  in  contact 
—with  chitin,  which  is  thick- 
ened in  such  a  way  as  to  form 
a  spiral  band  extending  along 
the  tube  and  serving  as  a  spring 
to  keep  its  walls  apart. 

The   digestive    tract   is    in 
most    groups   a  straight  tube, 
but  in  Insects  (Fig.  227)  it  may 
be  coiled  in  a  more  or  less  com- 
plex manner  and  differentiated 
into  several  parts.     Glands  of 
various  kinds  are  usually  asso- 
ciated with  it,  salivary  glands 
(Fig.  227,  sg)  opening  into  the 
anterior  portion  and  Mulpighian 
tubules  {inv\  in  connection  with 
the    posterior    portion,    being 
the   most    constant    in    occur- 
rence.    It  is  to  be  noted   that 
the  fore-gut  and   hind-gut  are 
ectodermal  in  origin,  and  that 
the  Malpighian  bodies  arising 
as  outgrowths  from  the  hind- 
gut  are  also  ectodermal,  differing 
thus  in  origin  from  the  similarly- 
named  organs   of  the   Arachnida,  which   are   apparently  of 
eudodermal   origin,  arising  from  the   mid-gut.     In   function 
both  orgaus  are  similar,  the  Malpighian  bodies  of  Tracheates 
being  excretory. 

The  nervous  system  in  the  less-differentiated  members  of 


Fig.   315.  — Figure   showing   the 
D18TKIBUT10N   OP    Trachea   in 
Aylm  pelargonii  (after  Witlaczil). 
At  =  antennse. 
g  =  glaud-duct. 
St  =  stigma. 
tr  =  trachea. 
1,  3,  3  =  thoracic  appendages. 


h  !' 


I  \ 


472 


INVERTEBRATE  MORPHOLOGY. 


the  type  consists  of  a  siipraoesopliageal  ganglionic  mass,  con- 
ncs.ted  by  circumcBsophageal  commissures  with  a  chain  of 
ventral  ganglia,  a  pair  of  ganglia  corresponding  typically  with 
each  segment.  In  the  Insecta  (Fig,  228)  more  especially, 
however,  considerable  concentration  occurs,  a  number  of  the 
})ostoral  ganglia,  or,  in  some  cases,  all  of  them,  fusing  to  a 
single  mass.  A  well-developed  stomatogastric  or  sympathetic 
nervous  system  occurs  in  all  forms,  arising  from  the  supra- 
uisophageal  ganglionic  mass  by  two  trunks,  which  unite  to 
form  a  single  nerve,  passing  to  the  digestive  tract,  and  in 
some  cases  provided  with  ganglionic  enlargements  both 
paired  and  unpaired. 

Sense-organs  of  various  kinds  are  well  developed  in  the 
Tracheata,  with  the  exception  of  Peripatus,  in  which  the 
only  definite  orpaus  of  special  sense  are  the  eyes.  In  other 
forms  the  antenna  and  other  portions  of  the  bodv  are  pro- 
vided with  hairs  connected  with  nerves  and  serving  as  tactile 
organs,  and  seta)  situated  upon  the  mouth-})arts  and  associated 
with  peculiar  nerve-endings  have  been  supposed  to  represent 
organs  of  taste,  and  others  again,  on  the  antenuje,  olfactory 
organs.  Eyes  .are  very  generally  present.  In  Peripidns  ami 
most  Myriapoda  simple  ayes  or  ocelli  are  alone  present ;  in 
l*evipatus  they  resemble  closely  in  structure  the  eycK  of  the 
Annelids  or  Mollusca  (e.g.  Ilalioiis,  see  Fig.  134),  but  in  the 
Myriapods  and  Insects  they  are  usually  more  complicattnl. 
Tims  in  a  young  larva  of  AciUm  (Fig.  216,  A\  a  water- 
beetle,  the  chitin  is  thickened  to  form  a  cornea  (J)  whicli  lies 
over  a  depression  of  the  liy^^oderMiis,  the  cells  at  the  bottom 
of  which  are  modified  to  form  a  retina,  each  being  contiuuoiiH 
at  its  inner  end  with  the  optio  nerve  (7t),  while  at  its  outer 
end  it  bej-rs  a  layer  of  chitin  (/).  The  cells  of  the  lip  of  tlio 
depression  have  ';onverged  together  h".'  as  to  meet  beneatli  the 
cornea,  which  is  indeed  formed  by  those  cells,  and  a  cavity  is 
tlius  enclosed  into  which  theio  i)r(.trude  from  among  tli« 
retinal  cells  largo  c^lls  {rmje)  with  chitin  dejiosited  on  tiicir 
adjacent  siirfaces.  In  a  hitev  sti'.ge  (Fig.  21(5,  II)  the  lij)s  of 
the  dopreK;:ion  have  unitevl,  a  continuous  corneal  liypoderiiiis 
[vh)  being  thus  jjrodiu'ed  ;  pigment  lias  been  deposited  in  the 
lateral  cells,  and  the  ictiinil  cells,  i)ig!heuted  near  their  outer 


TYPE  TRACHEATA. 


473 


eud8  and  in  continuation  witii  the  optic  nerve,  have  developed 
distinct  rods  (r)  at  their  outer  ends. 

In  the  Insecta  and  cccasionally  in  the  Myriapoda  (Scuti- 
gera)  there  are  m  addition  to  these  simple  ocelli  compound 
eyes  situated  at  the  sides  of  the  head  and  similar  in  structure 
to  the  compound  eyes  of  the  Crustacea.  Each  of  the  .m- 
luatidia  of  which  the   eye   is   composed,  and  tlere   may  be 


F,G.  216.-8ECTIONS  THKOaon  AN  OCELLUR  OF  A  LaUVA  OF  ^.wJ'l^N  {A)  A 
Veuy   loUNG  AND  IN   (B)  AN   OLDEIi   iSPECIMKN   (after  Pxtten) 

ir  =  inverted  rods.  ,,  =  ^erve 

'  =  '"";!^'''-  Pff  =  pigment. 

mgc  =  niedjiiu  gliint  cells.  r  =  rods. 

vb  =  vitreous  body. 

8.v(  >al  thousand  of  them  in  each  eye,  conftists  of  an  external 
cornea  (Fig.  217,  ro),  usually  more  or  less  hexagonal  in  outline 
giving  the  eye  a  faceted  appearance.  Beneath  the  covuoa 
iUB  two  cells  which  secrete  it  and  form  the  corneal  hypo,l,n- 
"lis,  and  below  these  again  come  four  cells,  the  crystallinp- 
ou.u,  cells,  which  may  (emonom  eyes)  or  may  not  (acmn.s 
oyes)  manufacture  a  crystalline  cone  (c\  and  finally  1  eneath 
tliose  IS  a  circiG  of  seven  retinular  cells  (four  in  Zepmna) 
t'ucj  one  of  which  is  pigmented  and  manufactures  a  portion 


jf  the  chitinlike  rhabdoni  (rh)  whicli  th 


cell,"' 


are  i)robably  contiisuous  at  their  inner 


ttiFwujiu  j    blltise 

ends  with  the 


optic  nerve.      Additional    pigment-cells  {pg)    separate    the 


•i 

i 


lil  V 


474 


INVEBTEBRA  TE  MORPHOLOO  7. 


various  ommatidia. 


CO 


pg' 


Rh 


Pg*" 


T 

Fig.  217.  —  Ommatidium 
OF  Eve  of  Munca  (after 

HiCKBUN). 

c  =  crystiiUiue  coue. 
CO  =  c'onieii. 
Pff  =  piijint'iit  cells. 
r  =  retiimlii-ceUs. 
Bh  =  rlmlHloia. 
T  =  tiacheii. 
tv  =  tmchctil  dllutatioD. 


Other  sense-organs  occur  in  the  various 
groups,  but  may  more  satisfactorily  be 
considered  in  the  special  descriptions 
of  these  groups. 

True  nephridia  similar  to  those  of 
the  Annelids  occur  in  Peripatus,  but  iu 
the  Myriapods  and  Insects  they  are  en- 
tirely wanting,  their  place  as  excretory 
organs  being  taken  by  the  Malpighiau 
tubules.  The  Tracheata  are  bisexual, 
the  reproductive  organs  being  typically 
paired  and  opjning  to  the  exterior  by 
ducts,  which  may  unite  before  reachiiij^ 
the  genital  orifice.  Accessory  struc- 
tures, such  as  a  bursa  copulatrix  for 
the  reception  of  the  penis  and  a  recep- 
taculum  seminis  occur  iu  the  female,  ami 
vesiculiB  semiuales  and  accessory  glands 
in  the  male.  The  region  of  the  body- 
wall  in  the  viciuit}'  of  the  reproductive 
orifice  is  in  the  Insects  frequently  iu- 
vagiuated,  adding  a  still  greater  com- 
plication, and  furthermore  the  terniiual 
portion  of  the  duct  in  the  male  is 
frequently  capable  of  being  evaginated 
and  thus  serving  as  a  penis,  while 
integumentary  elevations  or  processes 
of  the  last  abdominal  segment  iovm 
ovipositors  in  the  females. 


I.  Clash  Protraeheata. 

This  interesting  group  contains  but  a 
single  genus,  Pcripntm,  which  has,  lii>u- 
ever,  a  wide  distribution,  species  Ixiiij,' 
found  in  tne  West  Indies  and  South  Anu'rica,  at  the  Capt'  of 
Good  Hope  and  in  New  Zealand,  thus  indicating  an  origimd 
wide  distribution  of  the  genus  which  has  become  extinct 
except  iu  these  few  widely  separated  regions. 

Feripiitm  is  an  elongated  cylindrical  form,  measuring  iu 


TYPE  TR ACHE  AT  A. 


475 


jraeut  form 


the  Cape  species  (Fig.  218)  from  about  five  to  six  and  a  half 
centimetres  in  length,  and  is  found  beneath  stones  or  bark  o- 
amongst  decaying  wood.  The  body -wall  is  finely  annulatedi 
the  annuli  not,  however,  corresponding  to  segments,  and  the 
cuticle  is  thin,  small  papillae  being  scattered  all  over  the 
surface  of  the  body,  each  terminating  in  a  short  bristle 
The  head  is  but  poorly  marked  off  from  the  rest  of  the  body 
and  bears  a  pair  of  many-jointed  anteunje,  at  the  base  of  each 
of  which  towards  the  sides  of  the  head  is  situated  an  eye.  The 
mouth  lies  in  the  middle  of  the  ventral  side  of  the  head  and 
IS  surrounded  by  t  umerous  papilla?,  and  within  its  cavity  is 
situated  a  pair  of  jaws  furnisljed  with  strong  chitinous  sickle- 
shaped  teeth.     These  jaws  really  represent  the  second  pair  of 


Pig.  'i\9—Penpatm  capensis  (after  Moseley  from  Balfour). 
appendages,  the  third  pair  being  represented  by  two  short 
papillsB  lying  at  the  sides  of  the  head  and  having  at  their  tips 
the  openings  of  a  pair  of  glands  which  extend  far  back  into 
the  body-cavity  and  from  which,  when  tlie  animal  is  irritated 
there  is  violently  emitted  a  sticky  fluid,  whence  the  glands 
have  been  termed  the  slime-glands  (Fig.  219,  s(i).     There  is 
IK)  division  of  the  trunk  into  thoracic  an    ..bdomiual  regions 
and  It  bears  a  number,  varying  according  to  the  species  from' 
seven  to  twenty-one  pairs,  of  ambulatory  appendages,  each  of 
which  consists  of  a  proximal  stouter  and  somewhat  conical 
portion  bearing  rings  of   papillae  and  a  more  slender  short 
distal  portion  which  bears  at  its  tip  a  pair  of  claws  (ungues). 
Ihese  limbs  are  unsegmented,  differing  in  this  respect  from 
those  of  the  Myriapods  and  Insects,  and  are  also  soft  owing 
to  the  thinness  of  tlie  cuticle,  a  feature  wliich  has  suggested 
thfl  name  Mnlampixla  formerly  api.lied  to  the  tyne,  as  the 
presence   of  the    terminal   ungues   has   suggested 'the   term 
(hnfvhophom.     The  anus  is  situated  at  the  posterior  extremity 
Ox  the  bo<ly  and  has  ou  either   side  of  it  the  anal  papillw 
wliich  represent  the  last  pair  of  limbs. 


91 

lit. 


■ 

476 


IN  VERTEBRA  TE  MORPHOLOO  T. 


Beneath  the  thin  cuticle  is  situated  the  hypodermis,  auti 

beneath  this  a  well- developed 
dermal  muscular  system  re- 
calling that  of  the  Annelida, 
being  composed  of  an  outer 
layer  of  circular  muscles,  be- 
low which  are  diagonal  fibres, 
and  below  these  again  strougly- 
developed  longitudinal  muscles 
arranged  in  bundles,  two  of 
which  are  situated  dorsally, 
two  laterally,  aud  three  veu- 
trally.  In  addition  to  these, 
dorso  -  ventral  bands  occur 
passing  across  the  coelom  aud 
dividing  it  into  three  chambers, 
one  median  aud  two  lateral, 
and  special  muscles  are  also 
present  for  moving  the  limbs. 

The  ccelom  is  tolerably 
capacious  aud  consists  of  two 
portions.  The  larger  portion 
is   divided    by  partitions   into 

Pig.  219.-FiGunE  showing  the  f^^'^^'^^  subordinate  cavities 
Stuucture  OF  A  Female  Pm>aiMs  (F^K-  ^20)»  and  is  lined  throii^'h- 

out  by  a  peritoneal  epithelium 
which  covers  the  various  or- 
gans. From  it  are,  however, 
separated  certain  cavities  with 
detinite  walls,  which  staud  in 
relation  to  the  nephridia  and 
the  reproductive  organs  ami 
will  be  spoken  of  in  connection 
with  these  organs.  A  heart 
(Fig.  220,  h)  of  a  tubular  form 
extends  throughout  almost  the 
entire  length  of  the  body,lviiig 

oc)  incompletely  separated 

fenestrate 


(from  Hkbtwio). 

a  =  anus. 
ai  =  nnteuniB. 
ftwt  =  ventral  nerve-cord. 

d  =  inlostiiie. 
go  =  opening  of  reproductive  organ. 

0  =  ovary. 
og  =  brain. 

p  =  ))liarynx. 
sd  =  slinic-glands. 
80  =  nepliridia. 
sp  =  salivary  glands. 
tr  =  trachea). 

M  =  uterus. 


in  a  pericardial  space  (Fig.  220 
from  the  rest  of  the  ccjelom  by 


rausverse  par- 


Ik 

13- 

!■ 


TYPE  TRACHEATA. 


477 


tition.  A  pair  of  ostia  are  situated  on  the  dorsal  surface  of 
the  heart  in  each  metamere,  aud  pass  the  blood  into  the  heart 
from  the  pericardial  space.  Respiration  is  performed  by 
trachesB  (Fig.  219,  tr)  consisting  of  slender  unbranched  tubes 
which  arise  in  bunches  from  stigmata,  either  scattered  ir- 
regularly over  the  surface  of  the  body  in  considerable 
numbers  or  else  arranged,  as  in  P.  capemis,  somewhat  imper- 
fectly in  two  rows  upon  the  dorsal  and  two  on  the  ventral 
surface  of  the  body. 

The  mouth  opens  into  the  mouth-cavity  containing  the 
mandibles,  and  this  communicates  posteriorly  with  a  muscu- 
lar pharynx,  and  has  opening  into  it  the  ducts  of  two  long 
tabular  salivary  glands  {sp)  which  extend  through  more  than 
half  the  length  of  the  body.  The  pharynx  (p)  communicates 
by  a  short  oesophagus  with  the  stomach,  which  extends  as  a 
straight  tube  almost  to  the  extremity  of  the  body,  where  a 
short  rectum  places  it  in  connection  with  the  anus.  The 
pharynx  and  oesophagus  and  the  rectum  are  lined  with  chitin 
and  represent  the  fore-gut  and  hind-gut  of  other  Tracheates, 
the  stomach  being  the  mid-gut.  No  Malpighian  tubules  or 
other  diverticula  of  the  intestine  occur. 

The    nervous    system    shows    several    highly-interesting 
features.    There  is,  as  is  usual  in  metameric  animals,  a  supra- 
(jesophageal  ganglion-mass  (Fig.  219,  og)  composed  of  at  least 
two  and  probably  three  pairs  of  ganglia,  of  which  the  first 
supplies  the  antenuie  aud  the  second  the  mandibles,  while  a 
third  pair  lies  at  the  sides  in  close  contact  with  the  second 
pair  and  sends  nerves  to  the  oral  papilho.     These  latter  are, 
however,   postoral   and  ventral   in  position,  and   from   them 
tluu-e   extend  back  two   ventral    cords    {hm)   which    in    each 
iiietauiere  dilate  into  a  gaugliouic  swelliug.     The  two  ventral 
<'<»r(ls   are,  however,  widely   separated,  lying   in    the    lateral 
chauibers  of  the  cojlom  (Fig.  220),  and  are  connected  by  a 
liirge  number  of  cross-commissures — a  condition  which  recallH 
the  arraugemeut   in    i  •,      Amphiueurous  Mollusca  (see  Fig. 
124),  the  similarity  being  further  increased  by  the  facts  that 
the  two  cords  unite  behind  and  above  the  rectum,  as  in  the 
Soleuogastres,  aud  that  the  ganglion-cells  are  not  confined  to 
the  enlargements  but  are  scattered  all  along  the  cords.     Tho 


It 


478 


IN  VERTEBRA  TE  MORPHOLOO  Y. 


eyes  are  the  only  special  organs  of  sense ;  their  structure  has 
been  already  indicated  (p.  472). 

One  of  the  most  interesting  features  of  Peripatus  is  the 
occurrence  in  it  of  typical  nephridia  (Fig.  219,  so).  Upon  the 
under  surface  of  the  proximal  portion  of  each  limb,  with  the 
exception  of  the  penultimate  or  last  pair,  there  is  a  slitlike 
opening  which  leads  into  a  more  or  less  coiled  tube  lying  in 
the  coelomic  compartment,  which  extends  into  the  limb  and 


Fig.  220.— Transverse  Section  op  a  Peripatus  (after  Sbdowick) 
c  =  central  compartmeut  of  ccelom.     mg  =  slime-glands. 
g  =  reproductive  organ. 


h  =  heart. 
/  =  intestine. 

/  =  lateral  compartment  of  coilom. 
■ju  =  muscles. 


JV  =  ventral  nerve-cords. 
ne  =  nephridia. 
p  =  compartment  of  ccelom   which 

extends  into  the  limb. 
pc  =  pericardial  compartment  of  the 

ccelom. 


terminates  in  a  thin-walled  vesicle.  These  tubes  are  ne- 
phridia, the  terminal  vesicles  (Fig.  220,  ne)  representing  por- 
tions of  the  coelom  into  which  the  nephridia  open — a  fact 
indicated  by  their  erabryological  history.  The  nephridia  are 
thus  exactly  comparable  in  every  respect  with  the  nephridia 
of  Annelids,  communicating  at  one  extremity  with  the  exterior, 
and  at  the  other  with  th.«  coelomic  cavity.  It  i^  interesting  to 
note  that  the  development  of  the  salivary  glands  shows  that 


TYPE  TRACHEATA. 


479 


iructure  has 


shows  tliiit 


they  are  the  modified  nephridia  of  the  third  segment  of  the 
body,  that  which  bears  the  oral  papillse,  and  furthermore  it  is 
to  be  noted  that  in  the  last  or  next  to  last  (according  to  the 
species)  limb-bearing  segment,  in  which  nephridia  are  wanting, 
are  found  the  ducts  of  the  reproductive  organs— a  fact  whicih 
suggests  that  these  are  also  modified  nephridia.  This  idea  is 
confirmed  by  the  development  of  the  genital  ducts,  and  car- 
ries with  it  the  corollary  that  the  cavities  of  the  reproductive 
organs  (Fig.  220,  g)  are  portions  of  the  coelom,  just  as  they 
were  shown  to  be  in  the  Mollusca  (see  p.  288). 

In  addition  to  the  nephridia  there  are  associated  with  cer- 
tain  of  the  appendages  glands  which  open  on  the  under  sur- 
face  of  their  basal  moiety  and  are  termed  the  crural  glands. 
In  P.  capemis  they  are  present  in  all  the  appendages  except 
the  more  anterior  one,  and  the  slime-glands  are  simply  the 
highly-modified  crural  glands  of  the  oral  papillae,  those  of 
the  last  pair  of  appendages  in  the  males  of  this  species  being 
similarly  elongated  though  possessing  a  difi'erent  function. 
In  P.  Edwardsii,  however,  crural  glands  occur  only  in  the 
males,  and  in  these  only  in  a  few  segments  immediately  in 
front  of  that  bearing  the  reproductive  opening. 

The  Protracheata  are  bisexual,  the  female  usually  being 
somewhat  larger  than  the  male.  The  ovaries  are  paired, 
thvmgh  included  within  a  common  capsule,  and  lie  in  the  pos^ 
teiior  part  of  the  coelom.  They  are  continuous  with  two 
uteri,  which  immediately  at  their  origin  are  united  by  a  trans- 
verse  tube,  and  each  bears  a  receptaculum  ovorum  and  a 
receptaculum  seminis.  Beyond  this  each  continues  its  course 
along  the  side  of  the  body,  passing  backwards  to  finally 
unite  at  the  common  orifice,  lying  a  short  distance  in  front  of 
the  anus  on  the  ventral  surface  of  the  body.  The  testes  are 
slender  paired  structures  whicli  are  continuous  with  a  slender 
yas  deferens.  This  dilates  a  short  distance  from  the  testis 
into  a  vesicula  seminalis  and  then  unites  with  its  fellow  of  the 
opposite  side  to  form  a  slender  somewhat  coiled  tube,  the 
ductus  ejaculatoriuH,  in  the  terminal  portion  of  which  the 
spermatozoa  are  united  together  into  a  spermatophore.  The 
1  rotraciieata  arc  viviparous. 


I 

Wlk' 


480 


INVERTEBRATE  MORPUOLOOY. 


r<\ 


i 


Affinities  of  the  Protracheata. — Peripatus\&  a  highly-suggestive  form 
on  account  of  possessing  both  Annelidan  and  Tracheate  characteristics,  so 
that  it  has  been  generally  regarded  as  indicating  a  descent  of  the  Tracheate 
forms  from  the  Annelids.  Its  Annelidan  features  are,  first,  the  presence  of 
a  distinct  dermal  muscular  system;  second,  the  occurrence  of  crural  glands 
wh'ch  seem  to  be  homologues  of  the  glands  which  secrete  the  set®  in  the 
Annelida;  third,  the  possession  of  nephridia  corresponding  closely  to  those 
of  the  Annelids;  and  fourth,  the  structure  of  the  eyes.  On  the  other 
hand,  its  Tracheate  aflBnities  are  shown  by  the  claw-tipped  feet,  by  the 
adaptation  of  the  feet  (mandibles)  for  masticatory  purposes,  by  the  ten- 
dency towards  a  concentration  of  the  anterior  segments  to  form  a  head, 
and  by  the  occurrence  of  tracheae.  Both  these  sets  of  features  are  highly 
important,  and,  taken  with  the  wide  distribution  of  Peripatus,  point 
strongly  to  its  being  the  representative  of  a  connecting  link  between  Tra- 
cheates  and  Annelida,  a  phylogeny  which  may  be  considered  more  in  de- 
tail at  the  close  of  this  chapter. 


II.  Class  Myriapoda. 

The  Myriapoda  possess  a  distinct  head  composed  of  a  num- 
ber of  fused  segments  and  followed  by  a  distinctly-segmented 
body  formed  of  a  varying  number  of  segments,  all  of  which 
are  more  or  less  similar,  there  being  no  differentiation  of  a 
thorax  and  abdomen.  A  single  pair  of  appendages  as  a  rule 
is  borne  by  each  segment,  with  the  exception,  in  some  cases, 
of  the  last.  The  most  anterior  pair  are  usually  long  multi- 
artic'ilate  antennae,  the  second  pair  mandibles,  and  the  third 
and  fourth,  or  the  third  alone,  are  modified  to  form  maxilhi ; 
the  succeeding  pairs,  with  one  or  two  exceptions,  are  ambula- 
tory, and  are  jointed  and  tipped  by  a  claw. 

The  chitiuous  cuticle  is  generally  thick,  and  consequently 
no  definite  system  of  dermal  muscles  is  developed,  a  number 
of  separate  muscles  occurring  in  each  segment  for  moving  the 
appendages  and  the  various  segments  u])on  one  another. 
Glands  of  various  kinds  opening  upon  the  surface  of  the  btxly 
occur,  the  most  important  being  glands  or  protrusible  gland- 
ular sacs  situated  upon  the  basal  joints  of  a  number  of  the 
appendages  and  apparently  homologous  with  the  crural 
glands  of  Peripatus. 

The  heart  is  in  all  forms  verv  loner,  extendiner  tlirnncfli  tlie 
entire  length  of  the  body  behind  the  head,  and  possessing 


I 


TYPE  TRACHEATA. 


481 


just  as  many  chambers  and  pairs  of  alar  muscles  as  there  are 
trunk-segments.  The  number  of  stigmata  vary,  in  some 
forms  only  a  single  pair  occurring,  while  in  others  there  is  a 
pair  on  each  segment  of  the  trunk;  and  the  form  of  the 
tracheae  varies  also,  as  they  are  ciometimes  branched  and 
sometimes  arranged  in  bunches  composed  of  a  number  of  un- 
branched  tubes. 

The  digestive  tract  is  almost  always  a  straight  tube,  ex- 
tending through  the  body  to  the  terminal  anus.  The  mouth 
is  guarded  in  front  by  a  well-developed  upper  lip  or  labrum, 
while  the  fusion  of  the  maxillse  behind  it  in  many  forms  pro- 
duces a  lower  lip.  It  leads  into  an  ectodermal  fore-gut,  and 
this  into  an  endodermal  mid-gut,  which  is  usually  provided 
with  a  number  of  unbranched  diverticula  termed  hepatic  creca. 
One  or  two  pairs  o{  Malpighian  tubules  open  into  the  ante- 
rior end  of  the  ectodermal  rectum,  and  serve  as  excretory 
organs. 

The  nervous  system  except  in  the  head  region  shows  but 
little  trace  of  concentration,  there  being  as  a  rule  in  each 
segment  of  the  trunk  a  pair  of  ganglia.  The  antennal  ganglia 
are  fused  with  the  supraoesophageal  ganglionic  mass  which 
sends  off  branches  to  the  ocelli ;  these  may  be  quite  numer- 
ous, though  compound  eyes  do  not  as  a  rule  occur.  A  sympa- 
thetic system  is  present  as  in  other  Tracheates. 

There  are  no  nephridia  so  far  as  known  in  the  group,  the 
excretion  being  performed  by  the  Malpighian  tubules.  The 
reproductive  organs  are  paired,  and  open  to  the  exterior  in 
some  cases  by  paired  orifices,  but  more  usually  by  a  single 
opening,  which  may  be  situated  either  far  forwards,  or  else 
in  other  cases  near  the  posterior  extremity  of  the  body. 


» 
It 


irouch  flie 


1.  Order  Pauropoda. 

The  order  Pauropoda  contains  a  few  small  forms  in  which 
the  trunk  possesses  twelve  metameres  and  but  ten  pairs  of 
appendages,  which,  with  the  exception  of  the  rudimentary  first 
pair,  are  six-jointed  and  terminate  in  a  claw.  When  viewed 
from  the  dorsal  surface,  the  segments  appear  to  be  less  nu- 
merous than  the  appendages,  a  condition  which  results  from 


48d 


INVERTEBRA  TE  MORPEOLOO  Y. 


Fig.  221.  —  Pauropus 


tlie  fusiou  of  certain  metameres  iu  pairs,  so  that  two  pairs  of 
appeudages  appear  to  belong  to  some  of  the  segments,  the 
double  nature  of  which  is  further  shown  by 
the  occurrence  iu  them  of  two  pairs  of 
nerve-ganglia.  The  antenna)  (Fig.  221)  are 
remarkable  in  form,  consisting  of  a  four- 
jointed  basal  portion  which  bifurcates  at 
the  tip,  one  of  the  bifurcations  bearing  two 
long  liagella  and  a  peculiar  spherical 
stalked  body,  while  the  other  one  bears  a 
single  flagellum.  Mandibles  are  present, 
and  there  is  also  a  single  pair  of  but  poorly- 
developed  maxillae. 

Tracheae  or  other  respiratory  organs  are 
'suxkyHtrom'hzvyilh  ^ot  yet  known  to  exist,  nor  have  any  in- 
dications  of  a  circulatory  system  been  dis- 
covered up  to  the  present.     The    reproductive   opening  is 
situated  upon  the  second  trunk-segment. 

None  of  the  members  of  the  order  exceed  a  little  over  a 
millimeter  in  length.  The  genus  Pauropus  i^  characterized 
by  the  body  being  elongated  and  cylindrical,  and  by  its  active 
movements,  while  in  Eurypauropus  the  body  is  flattened  and 
relatively  broad,  and  the  movements  are  sluggish. 

3.  Order  Diplopoda. 

The  Diplopoda,  sometimes  termed  the  Chilognatha,  are 
popularly  known  as  the  Millipedes  on  account  of  the  commoner 
forms  possessing  an  unusually  large  number  of  appendages. 
The  body  is  usually  cylindrical  and  provided  with  a  hard 
cuticle,  and  many  forms  are  in  the  habit  of  rolling  themselves 
when  disturbed  into  a  ball  or  a  helixlike  coil,  thus  protect- 
ing the  more  delicate  ventral  surface  of  the  body.  The  an- 
tennae (Fig.  222,  at)  are  generally  seven-jointed  and  are  never 
very  long,  and  the  mandibles  are  strong  jaws  without  pulps. 
In  front  of  the  mouth  is  a  well-developed  upper  lip  (ul),  while 
behind  it  is  a  lower  lip  formed  by  a  fusion  of  the  maxillte  (nix). 
According  to  some  authors  this  lower  lip  represents  two  pairs 
of  appendages,  but  its  innervation  and  embryological  history 
seem  to  be  opposed  to  this  view.     The  segments  behind  the 


TYPE  TRACES  AT  A. 


483 


head  vary  in  number  in  different  genera  from  eleven  {Glo- 
meris)  to  over  one  hundred,  and  the  number  of  appendages  is 
much  greater  still,  since  the  majority  of  the  segments  bear 
two  pairs  of  limbs  and  in  reality  represent  each  two  meta- 
raeres.  The  four  or  five  anterior  trunk-segments  are,  however, 
single,  bearing  but  a  single  pair  of  limbs  (Fig.  222),  and  one 
of  them — in  some  cases  the 
first,  in  others  the  second,  but 
more  usually  the  third  (lulus) — 
is  entirely  destitute  of  appen- 
dages. The  last  few  segments 
also  carry  but  a  single  pair  of 
appendages,  as  does  also  the 
seventh  segment  in  the  males, 
the  appendages  of  which  are 
usually  modified  to  serve  as 
copulatory  organs. 

Stigmata  occur  on  each  of 
the  trunk-segments,  the  double 
segments  bearing  two  pairs, 
situated  on  the  ventral  surface 
near  the  coxal  joints  of  the 
limbs.  Each  one  has  in  connec- 
tion with  it  a  bunch  of  un- 
branched  tracheae,  a  condition 
recalling  somewhat  that  of  Peri- 
patus,  although  the  location  of 
the  stigmata  is  much  more  regular  and  definite.  Upon  the 
dorsal  surface  of  the  body  there  is  in  most  species  a  row  of 
pores  which  have  been  mistaken  for  stigmata,  but  are  really 
the  openings  of  glands  (gl  repugnatoria)  secreting  an  oily 
evil-smelling  fluid  which  serves  as  a  means  of  defeuca.  In 
the  genus  Polydesmus  the  secretion  contains  hydrocyanic 
acid.  Crural  glands  do  not  as  a  rule  occur,  but  protrusible 
warts  occurring  on  the  coxal  joints  of  a  number  of  legs  in 
some  genera  {Lysiopetalum)  have  been  regarded  as  homolo- 
gous structures. 

Tlie  nervous  system   has  the  cliaraftteristic  Myriapodan 
arrangement,  each  of   the  double  segments  possessing  two 


Fig.  232.— Anterior  Portion  op  a 

DiPIjOPOD. 

at  =  antenna. 
cop  =  copulatory  appendages. 
mx  =  maxilla. 

ul  =  upper  lip.  [segments. 

1,  2,  3,  4  =  the  four  anterior  trunk- 


\t 


484 


INVERTEBRATE  MORPHOLOGY. 


iSi 


*•  11 


pairs  of  ganglia.  Eyes  are  usually  present  and  are  always 
simple,  varying  in  number  from  two  to  as  many  as  eighty. 

The  Diplopoda  are  bisexual,  and  the  ovaries  or  testes  form 
a  single  mass  from  which  two  ducts,  or  one  which  later 
divides  into  two,  arise  and  pass  forward  to  open  on  the  ven- 
tral surface  of  the  body  between  the  second  and  third  trunk- 
segments.  The  embryos  when  first  hatched  out  possess  but 
three  pairs  of  legs,  situated  upon  the  first,  third,  and  fourtli 
segments  in  Strotigylosoma,  and  on  the  first,  second,  and  fourth 
in  Iidus,  one  or  more  segments  without  appendages  lying 
behind  the  fourth  pair.  By  successive  moults  new  segments 
and  appendages  are  added  and  the  form  of  the  adult  gradu- 
ally acquired. 

The  Diplopoda  live  for  the  most  part  under  stones,  etc., 
or  among  dead  leaves,  and  find  their  food  in  decaying  vege- 
table matter,  though  some  forms  will  attack  living  vegetation 
and  may  prove  thereby  injurious  to  gardens.  The  commonest 
form,  Iidus,  may  readily  be  obtained  under  stones  or  boards 
all  through  the  summer. 


3.  Order  Chilopoda. 

The  Chilopoda,  or  Centipedes,  are  very  different  in  their 
habits  from  the  Millipedes,  being  carnivorous  and  provided 
with  poison-glands  which  render  the  larger  forms  of  iScolo- 
pendra  dangerous  even  to  man.  The  body  is  as  a  rule  some- 
what flattened  and  less  hard  than  that  of  the  Diplopoda. 
The  antennae  (Fig.  223,  at)  are  usually  long,  with  at  least 
twelve  joints,  and  may  be  as  long  as  the  body,  while  the 
mouth-parts  are  much  more  complicat  *  than  in  the  Dip- 
lopoda. The  mandibles  and  upper  lip  ve.f  n^vie  the  c  '''r,;- 
spouding  parts  in  that  group,  but  the  mavillsB  {mx)  are  jaw- 
like, are  not  fused  together,  and  in  some  forms  (Geophihis) 
bear  a  palp.  Behind  the  maxillfe  comes  a  pair  of  second 
maxillse  (mx^),  which,  however,  do  not  serve  as  jaws  but  are 
TtaCvUved  to  a  pair  of  palplike  structures,  and  behind  these  again 
iz  u.  pirir  of  maxillipeds  (mxp),  the  appendages  of  the  first 
trunk-segment,  with  their  basal  joints  fused  to  form  a  lower 
lip  supporting  a  four-jointed  palp,  the  last  joint  of  which  is 


Hi 


TYPE  TRACHEATA. 


485 


Fig.  323.— Anteriou  Pou- 
TION  OP  A  CiuLoroD. 
at  =  antennae. 
mx^  =  umxilla. 
mx'^  =  second  maxillu. 
mxp  =  luaxilliped. 


clawlike  and  is  perforated   by  the  duct  of  a  poison-glaud. 

Each  trunk-segment,  of  which  there  may  be  over  a  hundred] 

bears  but  a  single  pair  of  appendages, 

there  being  no  compound  segments  as 

in  the  Diplopoda.     Each  leg  is  as  a 

rule  seven-jointed,  the  coxal  joints  of 

those  of  the  same  segment  being  widely 

separated,   and  there  is  no   modifica- 
tion of  the   seventh  pair  to   serve  as 

copulatory  organs.,  though  the  pair  of 

tlie    penultimate    segment  are    much 

reduced  in  size  and  lie  at  the  sides  of 

the  reproductive  orifice. 

Stigmata  are  usually  wanting  in  the 

first  three  trunk-segments,  but  occur  in 

a  certain  number  of  the  others,  lying 

usually  laterally  between  the  segments 

except  in  Scutigera,  in  which  they  have  a  dorsal  position. 
They  open  into  branched  tracheal  trunks  which  usually  an- 
astomose with  one  another,  though  in  Scutigera  they  open 
into  sacs  from  which  a  large  number  of  simple  uubranched 
tracheal  tubes  arise  arranged  in  a  bunch  as  in  the  Diplopoda. 
Crural  glands  occur  on  the  coxal  joints  of  several  of  the 
posterior  appendages. 

The  nervous  system  is  arranged  as  in  other  Myriapods,  and 
simple  eyes  are  usually  present,  in  Scutigera  only  being  closely 
aggregated  together  to  form  a  faceted  eye.  Tliis,  however,  is 
not  a  compound  eye  exactly  similar  to  that  of  the  Insects,  but 
is  to  be  regarded  simply  as  a  close  aggregation  of  simple 
eyes. 

The  reproductive  organs  are  usually  paired,  and  the  sexes 
separate.  The  ducts  unite  before  opening  to  the  exterior,  so 
that  there  is  but  a  single  opening  situated  on  the  antepenulti- 
mate segment  of  the  trunk,  the  appendages  of  which  are 
j,neatly  reduced  in  size.  The  embryos  of  Scolopendra  and 
GeopJiilm  leave  the  egg  with  almost  the  same  number  of  ap- 
pendages as  the  adult,  while  those  of  Scutigera  and  Lithohius 
possess  but  seven  pairs  of  legs  (in  addition  to  the  maxillipeds) 
HUil  gradually  acquire  others  by  successive  moults. 


486 


INVERTEBRATE  MORPHOLOGY. 


In  Scutigera,  a  form  wLicli  frequents  the  warmer  parts  of 
the  world,  the  dorsal  surface  of  the  body  is  covered  in  by 
eight  shieldlike  fok^s  which  conceal  a  certain  number  of  the 
segments,  which  are  about  fifteen  in  number.  Lithobius  has 
the  same  number  of  segments  a.id  is  common  under  stones, 
etc.,  as  is  also  Geophilvs  and  Scolopendra,  both  elongated  forms, 
the  former  usually  without  eyes,  while  the  latter  usually 
possesses  them  but  has  only  some  nine  or  ten  pairs  of  stig- 
mata. Some  of  the  species  of  Scolopendra,  especially  those 
living  in  warm  countries,  grow  to  a  considerable  size  and  are 
capable  of  inflicting  a  dangerous  wound. 


4.  Order  Symphyla. 

The  order  Symphyla  contains  a  number  of  small  forms 
referable  to  one  or  two  genera,  of  which  the  best  known  is  the 
genus  ScolopendreUa  (Fig.  224).  Unfortunately  the  details  of 
ti'e  structure  of  the  members  of  the  group  are  by  no  means 
well  known,  a  circumstance  all  the  more  to  be  regretted  siuce 
/ScolopendreUa  seems  to  possess  certain  Insect-like  features. 

The  body  is  elongated,  and  on  the  dorsal 
surface  possesses  a  number  of  plates 
which  overlap  slightly,  but  which  do 
not  correspond  in  number  with  the  ap- 
pendages. Tlie  head  bears  a  pair  of 
h)iig  many-jointed  antennre,  and  behind 
these,  in  the  region  of  the  mouth,  is  a 
pair  of  mandibles  and  a  single  pair  of 
maxilhe,  both  these  last-named  aj)- 
pendages  l)eing  deeply  imbedded  as  it 
were  in  the  tissues  of  the  head,  their 
Fio.  224.-  ScolopendreUa  ^'P«  ""^.V  projecting.  The  first  pair  of 
im7naculata  (fiow  lkunib).   truukappeudages  is  not  transformed  into 

maxillipeds  as  in  the  Chilopoda,  but  is 
ambulatory  in  function,  and  most,  but  not  all,  of  the  succeed- 
ing segments,  of  which  there  are  apparently  fourteen,  bear  a 
pair  of  tive-joiuted  legs  terminated  by  two  claws.  Attached 
to  the  coxal  joints  oi  most  of  tiiese  appendages  is  a  peculiar 
Hpurlike  process,  internal  to  whicli  is  situated  a  protrusible 


TYPE  Tli ACHE  ATA. 


487 


glandular  sac  which  is  probably  to  be  regarded  as  a  crural 
glaud.  The  last  pair  of  appendages  may  be  uiijoiuted,  each 
bearing  a  tactile  seta,  and  attached  to  the  last  segment  is  a 
pair  of  conical  processes  each  of  which  has  opening  at  its  tip 
the  duct  of  a  spinning-gland. 

Two  stigmata,  situated  at  the  base  of  the  antennre,  are  the 
..uly  ones  which  occur,  their  position  being  very  remarkable 
Tliey  open  into  bunches  of  branched  trachea3  which  extend 
throughout  the  greater  portion  of  the  body,  leaving  only  the 
appendages  and  the  posterior  part  of  the  trunk  destitute  of 
uu  air-supply.  The  Malpighian  tubules  attached  to  the 
limd-gut  are  very  long,  and  salivary  glands  opening  upon  the 
lauxilliu  are  present. 

Eyes  do  not  occur.  Both  t)  a  male  and  female  repro- 
ductive organs  are  paired.  There  is  but  a  single  genital  pore 
iu  either  sex,  situated  in  the  mid-ventral  line  towards  the 
front  of  the  fourth  truuk-segmen',  and  the  oviducts  or  vasa 
(loferentia  Uxiite  before  communicating  with  it.  Very  little  is 
kucwu  as  yet  concerning  the  development  of  SaP ■^pendrella. 
It  Jias  been  considered  by  some  to  show  marked  affinities 
with  the  lusecta,  and  the  name  given  to  the  order  implies  the 
l)f)ssibility  of  its  being  a  connecting  link  between  that  group 
iiud  the  Myriapoda.  The  spurlike  processes  have  been  re- 
garded  as  limb-rudimeuts,  in  which  case  it  seems  possible 
tliat  each  segment  may  really  be  a  double  segment  and  that 
the  Sym])hyla  have  close  affinities  with  the  Diplopoda. 


III.  Class  Insecta. 

The  class  Insecta  is  far  riciior  in  species  than  any  other 
clasHof  animals,  some  two  hundred  thousand  s})ocies  belonging 
to  it  being  known  to  exist,  and  of  these  about  eighty  thousand 
are  beetles.  A  very  large  number  are  i)rovided  with  organs 
of  flight  and  may  be  termed  aiirial ;  others  are  terrestrial, 
living  either  upon  the  surface  of  the  earth  or  excavating  bur- 
rows  beneath  its  surface;  while  some  have  adai)ted  them- 

-■" -"'  • .....,.-   ..,..!5.   .-I  iii-.,  aaa  t^ihcrs  aiu  even  murme, 

members  of  the  genus  IhthhaU'K  l)eing  found  on  the  surface 
of  the  ocean  many  miles  from  land.     Many  species,  living  as 


488 


IN  VERTEBRA  TE  MORPUOLOO  Y. 


they  do  upon  vej,'e table  food  either  in  the  adult  or  larval 
stages,  aud  occurriug  occasionally  iu  enormous  numbers,  form 
powerful  enemies  to  the  horticulturist  and  agriculturist,  the 
Eocky  Mountain  Locust,  for  example,  devastating  at  times 
the  crops,  while  fruit  and  forest  trees  are  injured  by  the  at- 
tacks of  other  forms. 

The  Insecta  differ  from  other  Tracheata  iu  having  the 
body  divided  into  three  well-marked  regions.  The  most  an- 
terior of  these  is  the  unsegmented  head,  bearing  the  autenuio 
and  the  masticatory  appendages,  and  immediately  following 
it  is  the  thorax,  composed  of  three  segments,  the  prothorax, 
mesothorax,  and  metaihorax,  each  of  the  last  two  bearing 
usually  a  pair  of  wings  upon  its  dorsal  surface,  while  pos- 
teriorly is  the  segmented  abdomen  composed  typically  of  ten 
segments,  sometimes  as  broad  as  the  thorax  at  the  junction 
with  that  region,  sometimes  contracted  to  a  narrow  stalk.  In 
many  cases,  however,  the  apparent  number  of  segments  falls 
below  ten  owing  to  the  fusion  of  certain  of  the  posterior  seg- 
ments  or  the  union  of  the  anterior  segment  with  the  thorax, 
and  in  the  Butterflies  and  two-winged  Flies  the  thoracic  seg- 
ments seem  to  be  reduced  to  two  owing  to  the  close  associii- 
tion  of  the  metathorax  with  the  first  abdominal  segment. 

Four  pairs  of  appendages  are  borne  by  the  head.  The 
autenme,  and  indeed  all  the  appendages,  vary  greatly  in 
shape  in  the  various  groups,  but  are  usually  long  slender 
raultiarticulate  structures  i)r()vided  with  sensory  hairs.  The 
masticatvry  appendages  are  a  pair  of  mandibles  aud  two 
pairs  of  maxilla",  which  are  variously  specialized  for  bitinj,', 
l)iercing,  or  sucking.  The  most  typical  condition  is  that  iii 
which  the  entire  apj)aratuH  is  adapted  for  biting  and  that  niav 
be  described  here,  leaving  special  modifications  to  bo  con- 
sidered  in  connection  with  tlie  orders  in  which  they  occnr, 
The  mandibles  (Fig.  225,  C)  are  strong  unjointed  toothed 
plates  which  meet  together  in  the  middle  line  and  are  ))!()- 
vided  with  strong  muscles.  The  first  maxilhe,  or,  as  they  are 
usually  termed,  the  nnixilhe  (Fig.  225,  li),  on  the  other  hand 
are  distinctly  i(jinte(l,  luuX  cniiHiHt  of  u  !)as<il  iiiiist  or  cn-ilo 
Hucceedt  '   ' 


I'y 


joint,  or  Hfipes,  which   bears  on  its 


outer  side  a  multiarticulate  palpus  (p)  and  terminates  in 


owe 


I'YPE  TR ACHE  AT  A. 


489 


lit  or  larval 
imbers,  form 
julturist,  the 
11^  at  times 
cl  by  the  at- 

liavJug  the 
?he  most  au- 
the  auteiiijiv 
\y  following 
e  prothorax, 
;wo  bearing 
,  while  pos- 
icallj  of  ten 
the  juuetion 
w  stalk.  In 
gments  falls 
osterior  seg- 
the  thorax, 
horacic  seg- 
ose  associa- 
gmeut. 
head.     TJie 

greatly  in 
:^ng  sloiuh'!' 
hairs.     The 

88    aU(l    two 

for  biting, 

u  is  that  in 

J(l  that  may 

to  be  con- 

the}'  occnr. 

ted   toothed 

tid  arc  ))i()- 

as  thev  aio 

other  ha  ml 

I  ^       tW     f*"  >•'/'> 

tVf    Ui     t  r  t  ;  t '  •  •, 

•oars  on  its 
lates  in  one 


or  two  unsegmented  plates  of  which  the  innermost  is  usually 

toothed.     The  second  maxill*  (Fig.  225,  A)  are  also  jointed 

and  are  fused  together  to  form  a  lower  lip,  or  laUum.     The 

fused    basal    joints   form    the 

sKbmentum    {sm),     the    second 

joints   the   mentum  (m),  which 

bears,  as  does  the  stipes  of  the 

maxillcTO,  a  jointed  pal})  (p)  and 

terminates   frequently   in    two 

uujointed   plate-like  processes. 

The  three  pairs  of  appendages 

of    the    thorax     are    typically 

ambulatory,    but  are    niodilied 

for  clasping,  swimming,  digging, 

etc.,  according  to  the  habits  of 

the  insect.    They  typically  con-  ^. 

sist  of  a  basal  joint,  the  coxa    ^^""  225.— Moutii-paiits  op  a  Bkr- 

•succeeded  by  one  or  two  small  ''"^f  ^''7/'"""«««- 

...  ,,       "^  ,  A  =  labium, 

joints,     the     trochanter,     upon  B  =  miuilla. 

which  follow  a  femur,  a   tibia,  C  =  miiudible. 

and  a  tarsus,  the  last  consisting 

of  five  (occasionally  four)  short  joints,  the  terminal  one  bear- 

ii:g  two  claws  or  ungues.     Abdominal  appendages  are  ropre- 

sented  only  by  cerci,  which  are  usually  many-jointed  structures 

occurring  near  the  posterior  end  of  the  body  in  many  groups 

of  lusecta  (Fig.  23G),  and  by  the  pairs  of  spurlike  processes 

which  occur  on  a  number  of  the  al)dominal  segments  of  the 

Thysanura  and  which  recall  the  spurs  on  the  trunk-segments 

of  Scolopendrella.     In   the  embryos   of   probably   all   forms 

rudimentary  appendages  are  found  on  some  of  the  abdominal 

segments,  but  they  later  disapjiear,  showing,  however,  a  de- 

scent  of  the  Insecta  from  forms  in  which  abdominal  a])pen- 

<lages   were  functional   in   the  adult.     Processes  of  various 

kunls,  such  as   stijJi.  ovipositors,  and  copulatory  organs,  are 

l'n'(|uontly  borne  by  the  jiosterior  abdominal  segments,  but 

these  do  not  seem  to  be  equivalent  to  ai)pendages. 

Ah  stated,  a  piiir  of  wiugs  is  usually  borne  by  the  meso- 

anil  metatho'-acic  segments.     These  structures  are  entirely 

wanting  in  the  lowest  insects,  the  Thysanura  and  Collembola, 


•  II 


490 


INYERTEBRA  TE  MORPHOLOO  7. 


as  well  as  in  certain  forms  belonging  to  other  groups  which 
have  lost  them  through  parasitism  (Mallophaya,  Pulex,  Melo. 
phiKjus)  or  other  causes  (Worker  and  Soldier  Termites,  Neuter 
Ants,  the  females  of  some  Moths).  They  are,  when  their 
possessors  are  first  hatched  out,  saclike  structures,  pro- 
cesses  of  the  body-wall,  tracheres  enclosed  within  blood-lacuuie 
extending  from  the  body  into  their  cavities.  Later,  however, 
the  walls  of  the  sac  come  into  contact,  the  cavity  being  ob- 
literated, the  trachere  with  the  blood-lacunae  in  which  they 
are  situated  remaining  enclosed  within  the  fiat  plates  so 
formed  and  constituting  the  so-called  veins  of  the  wing,  which 
have  in  most  species  a  characteristic  and  constant  arrange- 
ment. In  certain  forms  the  anterior  wings  become  more 
or  less  thickened  by  the  deposition  in  them  of  additional 
chitin,  and  may  form  hard  plates  {dytra,  Fig.  239)  which 
serve  as  a  cover  and  protection  for  the  posterior  wings,  which 
in  such  cases  are  alone  used  in  flight.  In  the  two-wiugeil 
Flies  (Fig,  244)  the  posterior  wings  are  very  much  reduced, 
being  represented  only  by  two  small  club-shaped  structures 
termed  "  balancers,"  attached  to  the  sides  of  the  metathonix. 

The  body  is  enclosed  in  a  chitinous  cuticle,  usually  of 
some  firmness  and  frequently  bearing  numerous  hairlike  pro- 
cesses, certain  of  which  serve  as  sense-organs.  Glands  open- 
ing on  the  surface  of  the  bodj'  also  occur  in  connection  with 
the  integiimont;  for  example,  peculiar  protrusible  glandular 
sacs  are  situated,  two  or  four  on  each  segment,  on  the  ab- 
dominal segments  of  tlie  Thysanura  and  Oollembola  close  to 
the  spurlike  abdonnual  appendages  present  in  those  forms, 
and  are  in  all  probability  homologous  with  the  similar  struc- 
tures of  ScoIopendreJhi  and  therefore  presumably  represent 
crural  glands.  These  glands  api)ear,  however,  to  be  wautin;,' 
in  other  insects.  Many  genera  of  Hemii)tera  possess  glands 
which  ))roduce  a  malodorous  secretion,  and  wax-glands  occur 
in  the  Plant-lice  {Cocckla')  and  Bees,  the  latter  also  po8S(>ss- 
ing  poison -glands  in  ccninection  with  a  complicated  stinginj,'- 
apjmratus,  which  is  a  modified  ovipositor. 

The  respiratory  stigmata  vary  greatly  in  number  in  dif- 
ferent groups  of  Insects.  In  the  wingless  Thysanura  and 
Collembola  there  are  usually  ten  stigmata  on  each  side  of  the 


groups  which 
Pulex,  Meh. 
□aites,  Neuter 
,  when  their 
ictures,  pro- 
blood-lacuu;e 
ter,  however, 
ity  being  ob- 
i  which  they 
at  plates  so 
)  wiug,  which 
;aut  arrauge- 
)ecome  more 
3f  atklitioual 
.  239)  which 
wings,  which 
3  two-winged 
iich  reduced, 
id  structures 
I  metathonix. 
e,  usually  of 
hairlike  i)ro- 
jrlands  opeii- 
inection  with 
)le  glanduhir 
t,  on  the  jtb- 
bola  close  to 
those  forms, 
liniilar  struc- 
>ly  represent 
o  be  wautiii;,' 
■)ssess  glands 
■glands  occur 
also  possess- 
,ted  stingiiifj;- 

miber  in  dif- 
ysanura  and 
)h  side  of  the 


TYPE  TRACHEATA.  49^ 

body,  two  being  situated  on  the  sides  of  the  thorax  and  eight 
ou  the  abdomen,  but  in  Cmnpodea  the  number  is  reduced  to 
hree  pan-s.  which  occur  upon  the  thorax.  In  the  winged 
orms  the  number  also  varies  somewhat,  but  there  are  agdn 
typically  ten  pairs,  arranged  as  in  the  Thysanura.  They  Tea 
into  short  trunks,  which,  in  a.mpo.te,  ramify  through  the 
body  without  anastomosing,  but  more  usually  they  are  uni  ed 
on  each  side  of  the  body  by  a  longitudinal  'tube,  to^;!  et 
pass  off  numerous  branches  penetrating  to  all  parts  of  the 
body,  and  transverse  connecting  tubes  passing  between  t le 
systems  of  the  two  sides  (see  Fig.  215).     In  certain  fonns 

dn  t  cW  "f     '    '"'  *''  longitudinal  tubes  are  frequenS; 

dilated    to    form    air-sacs,  as  in   the 

Bees,  or  numerous  air-sacs  may  occur 

which  may  be   more  or  less  emptied 

or  expanded  according  to  the  will  of 

the    iijsect,  the  specific  gravitv  of  the 

body    being     thus    altered.     'lu    the 

jupiatic   larvfe   Avhich    occur  in   some 

forms,  such  as  the  May-fiies  (Epheme- 

iKhe,  Fig.  220),   adaptations  occur   for 

the  breathing  of  air  dissolved  in   the 

water,  the  sides   of   the    body  in   the 

abdominal  region  being  prolonged  into 

;i  number  of  pairs  of  platelike  process- 

es,  into  which  branches  of  the  trachero 

project,  an    interchange    of   the   gases 

contained    in    the    trachea?   for    those 

dissolved    in   the    water   taking  i)lace 

through  the  walls  of  the  plates,  simi- 

liuly  to  what  occurs  in    the  brauchia) ^'"-    226.-Lauva    op    an 

of  the  Crustacea,  though  in  these  fornw     ^''"'^^'*'"^«""'""" ''«'msj. 

the  exchange  is  directly  with  the  gl":    "  =  ''''''''  '''''''^^ 

of  the    blood       These   structures  are    consequently  termed 

-heal  branchuo,  and  while  they  are  functional,  the'stign.ata 

'•'  closed   only  opening  when  the  adult  stage  is  reached  and  a 
torrestrud  life  adopted.     As  a  rule  the  tracheal  bn.,..].!     te 


i"own  off  at  the  m.)nlt  by  which  the  adult  L, 
nit  m  a  few  forms  they  persist  throughout  life 


orni  is  reached. 


1'' 

i 

I  ! 


492 


INVERTEBRATE  MORPHOLOGY. 


m 


\  I 


A  dermal  muscular  system  does  not  exist,  but  complicated 
and  well-developed  muscles  are  present  for  the  movement  of 
the  various  parts  of  the  body,  those  occurring  in  the  thorax 
bein^  especially  well  developed  and  serving  for  the  movement 
of  the  limbs  and  wings.  As  in  other  Tracheates  the  coeloin 
is  lacunar,  and  the  heart  lies  in  a  pericardial  sinus  below  the 
dorsal  surface  of  the  bodj',  alar  muscles  extending  from  it  to 
the  walls  of  the  body  and  partly  dividing  the  sinus  into  a  dor- 
sal and  a  ventral  chamber.  In  the  Thysanura  the  heart 
extends  from  the  posterior  thoracic  region  throughout  tho 
greater  part  of  the  abdomen,  and  consists  of  nine  chambers 
separated  by  valves  and  each  provided  with  a  pair  of  ostia  ami 
a  pair  of  alar  muscles.  In  the  majority  of  forms  (Fig.  227,  //), 
however,  the  heart  is  entirely  confined  to  the  abdominal 
region,  and  the  number  of  chambers,  though  frequently  as 
high  as  eight,  may  be  greatly  reduced.  An  aorta  extends 
forwards  from  the  anterior  chamber  into  the  head,  in  the 
Butterflies  (Fig.  227)  dilating  in  the  thorax  to  form  a  second- 
ary heart  {ciK),  and  sends  off  branches  which  quickly  empty 
into  the  lacunar  spaces. 

The  greater  portion  of  the  abdomen  is  occupied  by  a 
peculiar  tissue,  termed  the  fat-body,  in  which  the  various 
organs  are  more  or  less  imbedded,  and  which  receives  its 
name  from  the  fact  that  its  cells  contain  globules  of  fatty 
matter,  and  in  the  adult  insect  usually  also  concretions  of  uric 
acid.  It  is  not  necessarily  confined  to  the  abdomen,  but  may 
extend  into  the  thorax  or  even  into  the  head.  In  certain 
Beetles— the  Fireflies  (LampyridjB)  and  Pyrophorus  of  the 
West  Indies — certain  regions  of  the  body,  especially  the 
abdomen,  and,  in  Pyrophorus,  two  spots  upon  the  thorax,  give 
out  under  certain  conditions,  apparently  under  control  of  the 
animal,  a  very  bright  light,  usually  spoken  of  as  a  phosphoies- 
cence.  The  tissue  which  produces  the  light  is  tlie  fat-body, 
or  special  portions  of  it  abundantly  sui)plied  by  trachea',  ami 
the  process  seems  to  be  one  of  oxidation  of  phosphorus, 
containing  substances.  The  exact  nature  of  the  phenoniciiou 
is  but  poi)rly  understood  at  present,  and  it  is  not  possible  hy 
any  means  at  our  disposal  to  produce  in  the  laboratory  a 


TYPE  Tit  ACHE  AT  A. 


493 


light  equal  in  iuteusity  to  that  of  the  Firefly  with  the  espenili- 
tare  of  as  little  euerg3% 

The  digestive  tract  is  as  a  rule  much  more  complicated 
than  ill  other  classes  of  Tracheates  aud  is  generally  more  or 
less  twisted  or  contorted  in  the  abdominal  region,  so  that 
usually  it  is  longer  than  the  body.  The  mouth  is  bounded 
in  front  by  a  usually  large  upper  lip  or  labrum,  generally 
described  with  the  mouth-parts,  but  distinguished  from  them 
in  not  representing  a  pair  of  appendages.  The  anterior 
portion  of  the  intestine,  the  fore-gut,  is  ectodermal  in  origin 

ah 


as 


Fig.  227.— Structure  op  Butterfly,  Danais  archippus  (after  Buroess). 


a  ■-=  ttiiteuim 
ag  =  accessory  gland. 
ah  =  accessory  heart. 
an  =  abdominal  ganglion. 
be  =  bursa  copulalrix. 

e  —  crop. 

cc  =  canal  uniting  be  aud  oviduct. 
ce  =  cerebral  ganglion. 

h  =  heart. 

I  =  thoracic  limbs. 


mv  =  Malpighian  tubules. 

t)cl  =  oviduct. 

ov  =  ovary. 
ph  =z  pharynx. 

pi  =  palp. 
s  =  stomach. 

sg  =  salivary  gland. 


tg  =  thoracic  ganglion. 
I-TIT  =  thoracic  segments. 
1-9  =  abdominal  segments. 

as  in  other  Tracheates  and  consists  of  a  mouth-cavity 
into  which,  or  in  its  neighborhood,  the  ducts  of  one  or 
more  generally  well-developed  salivary  glands  (Fig.  227,  .vr/) 
open.  The  secretion  of  these  glands  varies  considerably  in 
different  forms,  one  of  the  pairs  present  in  the  larva)  of  "the 
Biitterflies  and  certain  Moths  being  transformed  into  silk- 
spinning  glands,  the  silk  of  the  Silkworm  being  a  product  of 
their  activity.  When  digestive  the  secretion  seems  to  have 
a  peptonizing  effect  as  well  as  the  power  of  transforming 
starch  into  suLmr,  jiiid  is  consequently  of  fongidorable  diges- 
tive importance.     The  mouth-cavity  opens  behind  into  an 


494 


IN  VERTEBRA  TE  MORPHOL  OQT. 


oesophagus,  whose  posterior  region  is  frequently  dilated  iuto  a 
crop  (Fig.  227,  c)  which  in  some  Beetles  is  lined  with  chitinous 
teeth  or  bars  and  whose  walls  are  muscular,  the  apparatus 
probably  serving  for  a  further  mastication  of  the  food.  The 
mid-gut  which  succeeds  the  crop  is  usually  dilated  into 
a  stomach  (s),  lined  in  some  cases  by  glandular  cells,  or, 
in  others,  having  opening  iuto  it  numerous  glaudukr  diver- 
ticula, the  so-called  liver-pouches.  The  hind-gut,  like  the 
fore-gut  of  ectodermal  origin,  has  opening  into  its  anterior 
extremity  the  Malpighiau  tubules  {mv),  which  vary  consider- 
ably in  number,  amounting  to  nearly  one  hundred  in  some 
Hymenopterans,  though  more  usually  limited  to  from  four  to 
eight.   They  are  excretory  in  function,  and  are  apparently  the 


Tig.  228.— Different  Akiiangements  op  the  Nertous  System  in  Insect j 
(from  Qeoenbaur).     A,  Termes  ;  B,  Dytiscus  ;  C,  a  fly. 

only  excretory  organs  which  occur.  The  anus  is  situated  at 
the  extremity  of  the  body,  and  in  close  proximity  to  it  odor- 
iferous  glands  frequently  open  into  the  hiud-gut,  serving  as 
organs  of  defence.  In  some  cases  they  secrete  an  acrid  fluid 
which,  as  in  the  Bombardier  beetle  {Brachimis),  can  be  ex- 
pelled with  almost  explosive  force. 

The  nervous  system  in  forms  where  it  shows  the  least 
amount  of  modification  (Fig.  228,  A)  consists  (1)  of  a  supia- 
oesophageal  mass  composed  apparently  of  three  pairs  i)f 
ganglia  and  supplying  the  eyes  and  the  antennre  ;  (2)  of  a  sul)- 
CGSophageal  mass  composed  also  of  three  pairs  of  ganglia 
supplying   the   segments   indicated    by   the   mandibles,   the 


TYPE  TRACHEA TA. 


495 


ilated  iuto  a 
th  cLitinous 
e  apparatus 
I  food.  The 
Llilated  iuto 
ir  cells,  or, 
dulcr  diver- 
ut,  like  the 
its  auterior 
vy  cousider- 
'ed  iu  some 
rom  four  to 
pureiitlj  the 


EM  IN  Inbect: 
Y- 

situated  at 
to  it  odor- 
serving  ilS 
acrid  fluid 
can  be  ex- 

s  the  least 
)f  a  supiii- 
e  jjairs  of 
2)  of  a  sul)- 
of  ganglia 
libles,   the 


laaxillee,  and  the  labium  ;  (3)  of  three  pairs  of  ganglia  in  the 
corresponding  thoracic  segments  ;  and  (4)  of  a  chain  of  ab- 
dominal ganglia,  a  pair  occurring  in  each  segment  except 
usually  the  last  two  or  three,  in  which  a  compound  ganglion 
occurs.  Frequently,  however,  this  typical  condition  is  modi- 
fied by  a  greater  or  less  concentration  of  the  various  ganglia, 
the  thoracic  ganglia  fusing  to  a  single  mass,  as  may  also,  more 
or  less  perfectly,  the  ganglia  of  the  abdominal  chain  (Fig.  228, 
7>),  and  the  latter  may  even  unite  with  the  thoracic  ganglia  to 
form  a  single  mass  situated  in  the  thorax,  as  in  certain  two- 
winged  flies  (Fig.  228,  C).  A  visceral  system  is  usually  pres- 
ent  arising  from  the  supraoesophageal  (cerebral)  mass  and 
being  distributed  to  the  walls  of  the  digestive  tract. 

The  antennffi  of  insects  seem  to  act  as  sense-organs,  and 
serve  apparently  to  control  the  flight,  since  when  removed  the 
insect  is  not  able  to  fly  with  its  accustomed  ability.     So  too 
it  seems  probable  that  in  the  Ants  and  Roaches  these  appen- 
dages are  the  seat  of  the  olfactory  sense,  and  iu  the  Mosquito 
it  seems  that  certain  hairs  upon  them  may  be  auditory  in 
function.     Compound  eyes,  frequently  consisting  of  several 
thousand  omraatidia,  are  usually  present,  as  well  as  a  small 
number  of  simple  eyes  (ocelli)  situated  upon  the  dorsal  sur- 
face of  the  head.     Special  organs,  which  have  usually  been 
considered  auditory,  also  occur  in  many  forms,  varying  con- 
siderably in  complexity.     In  its  simple  form  such  an  organ 
vnsists  of  a  single  nerve-fibre  which  dilates  into  a  ganglion- 
prolonged  into  a  terminal  hair  which  is  enclosed  within 
.  sheath  fastened  at  one  end  to  the  wall  of  the  body.     This 
whole  apparatus  is  termed  a  chordotonal  organ,  and  T.iere  is 
usually  attached  to  the  sheath  just  where  the  hair  arises  from 
the  ganglion  a  ligament,  which  is  also  inserted  iuto  the  body- 
wall.     In  the  majority  of  cases  a  number  of  ganglion-cells  and 
liairs  are  associated  to  form  a  chordotonal  organ  (Fig.  229) 
the  various  hairs  sometimes  being  grouped  within  a  single 
slieath,— sometimes,  however,  spreading  out  in  a  fanlike  man- 
lier, each  possessing  its  own  sheath.   These  organs  occur  in  vari 
ous  parts  of  the  body,  on  the  antennsp  or  on  the  lim])s      In 
tlie  grasshoppers   (Acridiidre)   the   first   abdominal  segment 
hears  on  either  side  a  thin  tense  membrane,  a  thinned  portion 


496 


INVERTEBRATE  MORPHOLOGY. 


of  the  cuticle,  recalliug  the  tjmpauic  membraue  of  the  human 
ear,  beneath  aud  iu  couuection  with  which  is  a  chordotoual 
apparatus,  further  improved  by  the  occurrence  in  close  prox- 
imity to  it  of  a  saclike  enlargement  of  a  trachea  which  serves 
as  a  resonator.  Similar  organs  occur  in  pairs  on  opposite 
sides  of  the  tibiro  of  the  first  pair  of  legs  in  the  Crickets 
(Gryllidse),  and   seem  from   their  structure   to  be  auditory 


Fig.  229.— Subgenual  Chordotonal  Organ  of  the  Tibia  op  the  Second 
Thoracic  Appendage  of  Isopteryx  (after  Graber  from  Lang). 
bk  =  blood-corpuscles.  gz  =  ucrvo-cells. 

c  =  intcgmeut.  tr  =  trachea. 

es  =  teiralnal  ligaiueut.  se  =  teniiiual  balrs  and  sheaths. 

organs,  whence  the  conclusion  that  the  more  simple  chordo- 
tonal  organs  also  subserve  this  function. 

It  is  interesting  to  note  that  the  males  of  the  forms  provided  -vitli  a 
tympanal  organ  possess  the  power  of  making  a  harsh  or  sharp  chirpiiiir 
noise,  produced  in  the  Grasshopper  by  rubbing  the  femora  of  the  hind  legs 
which  are  furnisiied  on  their  inner  surfaces  with  a  row  of  line  teeth,  ovor 
the  strong  marginal  veins  of  the  anterior  pair  of  wings  ;  and  in  the  Crickets 
and  Locustida?  by  rubbing  together  the  two  anterior  wings,  a  row  of  toetii 
upon  a  vein  of  one  wing  working  upon  a  projecting  smooth  vein  of  the 
other.  The  male  Cicadas  also  make  a  similar  noise,  the  stridulatiiig  appa- 
ratus resembling  that  of  the  Grasshoppers,  and  in  all  cases  it  seems  to  be  a 
sexuj'l  characteristic  serving  to  attract  the  females. 

The  sexes  are  separate,  and  a  more  or  less  distinct  sexual 
dimorphism  occurs,  the  males  being  usually  smaller  and  more 
slender  than  the  females.  In  some  cases,  as  in  the  TnKS(i('k- 
moth  (Orgyia),  the  female  lacks  wings  and  has  a  very  different 


TYPE  TRACHEATA. 


497 


appearance  from  the  males,  and  iu  many  Beetles  the  male  is 
adorned  with  spines  and  tubercles  upon  the  head  which  are 
but  rudimentary  or  absent  in  the  female.  Differences  in  the 
shape  of  the  antenna  and  the  presence  or  absence  of  stridu- 
lating  organs  also  serve  to  distinguish  the  two  sexes  iu  some 
of  the  groups.  In  a  few  forms  a  polymorphism  is  produced 
by  the  failure  of  certain  individuals  to  reach  sexual  maturity 
and  by  the  assumption  by  them  of  certain  special  structural 
characteristics.  Examples  of  such  cases  are  afforded  by  the 
Bees,  Ants,  and  Termites,  the  workers  of  the  first  two  groups 
bemg  immature  females,  while  in  the  Termites  (Fig.  237)  the 
so-called  neuters  may  be  either  males  or  females,  always, 
however,  immature. 

The  ovaries   (Fig.   227,  ov)  are  paired   and  consist  of  a 
varying  but  usually  rather  large  number  of  tubes,  which  start 
from  a  common  basis.     At  the  extremity  of  each  tube  is  the 
germ-producing  region,  the  rest  of  the  tube  beiug  divided  into 
a  series  of  chambers  each  of  which  contains  an  ovum  sur- 
rounded by  a  lajer  of  follicle-cells.     Not  unfrequently  the 
chambers  are  arranged  more  or  less  distinctly  in  pairs,  the 
lower  one  of  each  pair  containing  an  ovum,  while  the  upper 
contains  a  number  of  small  cells  similar  iu  appearance  to  the 
primary  germ-cells,  but  which  serve  as  nutrition  for  the  ovum 
which  gradually  absorbs   them   (see   Fig.   20).     From   each 
ovary  an  oviduct  arises,  the  two,  however,  soon  uniting,  and 
receiving,  usually  not  far  from  the  unpaired  orifice,  the  ducts 
of  various  glands  {ag)  whose   secretion  serves  to   cause  an 
adhesion   of   the  ova    to  the   structures   on   which   they  are 
deposited.     A  receptaculum  semiuis  is  usually  present,  and 
there  is  frequently  a  large  pouch,  partially  separated  from  the 
oviducts,  which  receives  the  male  organ  during  copulation  and 
is  termed  the  bursa  copulatru-  (be).     The  genital  orifice  is  situ- 
ated on  the  ventral  surface  of  the  ninth  abdominal  segment 
and  is  usually  surrounded  by  a  number  of  papilhe,  or  some- 
times by  long  processes,  which  serve  as  ovipositors  and  are 
to  be  regarded  simply  as  processes  of  the  segments  from  which 
they  arise  and  not  as  modified  limbs. 

The   testes  are   also   paired,   each   being  composed  of   a. 
number  of  separate  spherical  or  tubular  portions.     The  ducts. 


tss 


498 


INVERTEBRA TE  MORPHOLOO  Y. 


from  these  various  portions  on  each  side  unite  to  form  a  vas 
deferens  which  may  dilate  into  a  vesicula  seminalis  and  then, 
uniting  with  its  fellow  of  the  opposite  side,  forms  the  ductus 
eJHCulatorius.  Occasionally  the  vesicula  is  unpaired  arising 
from  the  point  of  union  of  the  two  vasa  deferentia,  and  very 
frequently  accessory  glands  occur.  The  ductus  ejaculatorius 
opens  usually  on  the  ventral  surface  of  the  tenth  abdominal 
segment,  and  projections  of  the  body-wall  in  the  vicinity  of 
the  orifice  form  a  groove  or  tube  through  which  the  sperma- 
tozoa, usually  united  into  spermatophores,  are  introduced 
into  the  bursa  copulatrix  of  the  female. 

Parthenogenesis   occurs  as  a  normal  process  in  certain 
Insects,  though  always  associated  with  true  sexual  reproduc- 


FiG.  2.2Q.— Aphis  mail.  Winged  and  Wingless  Forms  (from  Packard). 

iiou.  Examples  of  it  are  found  in  certain  Coccidee  {Aspidio- 
tits)  and  in  some  of  the  Gall-wasps  (Cynipidse),  the  fertilized 
ova  producing  both  males  and  females,  while  in  the  Bees,  for 
example,  in  which  both  fertilized  and  unfertilized  ova  are  de- 
posited, the  latter  give  rise  to  drones  or  males  alone,  while 
workers  or  queens,  i.e.  the  females,  develop  from  the  fertilized 
ova.  Occasionally  heterogony  occurs,  as  in  the  Plant-lice 
(Aphidaj).  These  forms  under  favorable  conditions  of  tem- 
perature and  food  produce  viviparously  usually  wingless  indi- 
viduals, not,  however,  from  true  ova,  but  by  a  process  which 
may  rather  be  compared  to  internal  budding,  as  in  the  Rediiv 
of  certain  Trematoda.  Generation  after  generation  of  such 
individuals  may  be  produced  during  the  summer,  but  on  the 


TYPH  TU ACHE  AT  A. 


49^ 


5m  Packard). 


approach  of  cold  weather  or  ou  the  exhaustion  of  the  food- 
supply  males  and  fen. ales  appear  by  which  true  fertilized  ova 
are  produced,  and  fr  nn  these,  surviving  the  winter,  viviparous 
lieterogonous  females  develop. 

In  the  genus  Phylloxera,  whicli  has  played  such  havoc  ou  grape-vine^ 
ill  France,  a  greater  complication  of  generations  occurs.  A  winter  egg, 
which  has  survived  beneath  the  bark  of  the  vine,  gives  rise  to  wingless 
forms  which  migrate  to  the  roots,  and  there  produce  numerous  genera- 
tions. After  a  time  winged  forms  appear  which  ascend  from  the  roots 
and,  reproducing  parthenogenetically,  increase  rapidly  in  number  and  serve 
to  distribute  the  species  over  wider  areas.  Certain  of  these  jjroduce  small 
ova  from  which  males  develop,  and  others  larger  ones  which  give  rise  to 
females,  both  sexes  being  destitute  of  both  wings  and  digestive  tract,  and 
by  these  forms  the  fertilized  winter  eggs  are  produced. 

In  certain  flies  {3Iiastor,  Cecidomyia)  psedogenesis  occurs» 
the  female  reproductive  organs  becoming  mature  while  the 
iusect  is  still  in  the  larval  stage,  and  the  ova,  developing  par- 
thenogenetically within  the  body,  give  rise  to  another  gen- 
eration of  larvsB.  This  process  may  be  repeated  several 
times,  the  last  generation  of  larva)  developing  into  the  adult 
form  (see  Fig.  29). 

The  more  primitive  Insects,  the  Thysanura  and  Collem- 
bola,  leave  the  egg  in  a  form  resembling  the  adult,  differing 
from  it  only  in  size  and  in  the  immaturity  of  the  reproduc- 
tive organs,  and  i)ass  through  no  marked  metamorphosis 
during  their  post-embryonic  development.  Such  forms  are 
termed  ametaholic.  A  similar  absence  of  metamorphosis  i^ 
found  in  certain  forms  degenerated  by  parasitism  and  lacking 
Avings,  but  these  have  evidently  descended  from  winged  forms 
which  passed  through  a  certain  amcmt  of  metamorphism» 
so  that  the  ametabolism  is  secondary  and  should  be  distin- 
guished from  the  primitive  ametabolism  of  the  Thysanura. 
In  the  majority  of  winged  forms,  however,  a  more  or  less 
pronounced  metamorphosis  occurs.  In  the  simpler  cases  the 
young  are  distinguishable  from  the  adults  by  the  absence  or 
but  slight  development  of  the  wings,  which  become  larger 
after  successive  moults,  the  adult  form  being  thus  gradually 
acquired.  In  tliese  cases  of  gradual  metamorphosis  the 
habit '  of  the  adult  and  larva  are  similar,  but  where  they 


S3 


500 


INVERTEBRATE  MORPHOLOGY. 


differ  greater  cliauges  result,  leading  to  hemimetahoUsm.  This; 
occurs,  for  iustauce,  iu  the  Fish-flies  (Ephenieridse)  aud 
Dragou-llies  {Lihelhda),  in  which  the  larva)  are  adapted  for  au 
aquatic  life  and  possess  tracheal  brauchiie  (Ephemeridse)  aud 
other  features  which  are  lost,  either  gradually  by  successive 
moults  or  suddenly  at  the  last  moult,  the  adult  winged  Dragon- 
fly,  for  instance,  issuing  from  a  peculiar  aquatic  larva  with 
the  merest  rudiments  ol  wings. 

Finally,  a  large  number  of  forms  are  hohmetaholic.  In 
such  cases  the  habits  of  the  larva3  are  different  from  those  of 
the  adults;  for  instance,  the  larvje  of  the  Butterflies,  Wu^ 
caterpillars  (Fig.  231),  are  wornilike  creatures  with  power- 


mpmmmmm 

Fio.  231.— Lauva,  ri:i>A,  and  l.MAfio  uv  I'lcris  oleracea  (ivom  Riley), 

ful  jaws  feeding  ou  plant-tissues,  while  in  the  adults  the  mouth- 
parts  are  adapted  for  sucking.     The  transformation  from  the 
larva  to  the  adult  is  accomplished  by  the  intervention  of  a 
resting  stage  or  pupa,  dur-ng  which  no  uutiition  is  taken,  ami 
when    the    transformation    takes    place   the    fully.deveh)}i('(l 
insect  or  imago  issues  from  the  ru])tured  skin  of  the  ))ii)ia. 
The   pupa  varies  considerably  in  form  in  different   grou]).s, 
in   some   being   enclosed  in  a  silken  case  manufactured  by 
the  larva  before  the  last  moult  and   termed  a  cocoon.     In 
some  cases  the  adult  apjiendages  project  from  the  bpdy  of 
the  pupa  (pupa  JiberaX  but  iu  other  cases  they  are  united 
with   the  surface  of   the  body   and  but  indistinctly   visible 
{pupa  ohtecta),  au  arrangement  usually  found  in  the  Buttor- 
flies,  whose  pnpjo,  owing  to  their  frequent  brilliant  coIoim- 
tion,  are  termed  chrysaluh.  a  term  which  lias  been  somewhat 
incorrectly  extended  to  the  mummy-like  puptr  of  other  forms. 


TYPE  TRACHEA TA. 


501 


liually,  m  some  of  the  two-winged  ilies  the  pupa  is  euclosed 
Mithiu  the  Lxst  larval  skin,  possessing  then  a  cvliudiical  form 
without  any  indication  of  the  adult  Umbs  (pupa  cocwctata). 
A  metamorphosis  in  ^vhich  a  distinct  pupa-stage  occurs  is  said 
to  be  "complete"  in  contradistinction  to  the  hemimetabolic 
form  frequently  spoken  of  as  "incomi)lete." 

Mention  sliould  bo  made  here  of  the  dimorpliisu,  or  polymorphism  whidi 
o.:ct.rs  m  certai..  adult  Insects.     It  has  already  received' passing  n.e.itiun 
M>.  497),  but  in  addition  to  the  frequently-occurriuf,'  sexual  dimorphism 
there  occurs  in  forms  which  live  together  in  colonies  a  i)olvmorphism  asso- 
ciated with  a  division  of  labor  on  the  parts  of  the  members  of  the  colony 
liius  m  the  Bees  there  are  found  the  drones  or  males  with  heavy  bodies 
Ih.'queen  or  female,  as  large  as  the  drones  but  with  a  much  more  fjlonder 
body,  and  the  workers,  which  are  sterile  females  (listingiiish,.d  bv  their 
smaller  size  and  by  other  features,  such  as  a  peculiar  moditication'of  the 
lilMas  of  the  last  pair  of  legs  which  a.lapt  them  for  the  collection  of  pollen 
Ironi  the  (lowers  which  they  visit.     Among  the  Ants  a  similar  trim..rpl,ism 
orcurs,  males,  females,  and  neuters  or  workers  constituting  the  colony  and 
iM  some  f  epical  forms  the  workers  are  of  two  kinds,  namely,  ordinary 
workers  wh  1  small  heads  and  mandibles,  and  soldiers  with  large  heads  anil 
strong  prominent  mandibles,  whose  functions  are  indicated  by  the  popular 
name  applied  to  them,  though  guards  would  perhaps  be  nrnre"  appropriate 
luially,  among  the  Termites,  popularly  known  as  the  White  Ants   four 
lorins.  I.e.,  males,  females,  workers,  and  .soldiers,  al.so  occur. 

In  certain  Buttertiies  a  peculiar  form  of  dimorphism  ..r  trimorphi.sm 
termed  "seasonal  dimorphism"  occurs,  an  excellent  exami)le  of  it   bein- 
<'thT..d  by  the  American  Popff'o  AJax,  of  .vhieh  there  have  been  described 
(luve  distinct  varieties,  diflVriiig  markedly  in  e.,l..rati..n  both  in  the  males 
aiul  (ho  females,  and  distinguished  as  the  yarielies  W„fs/u,\  Tvhmouhhs 
iiiu\  Marce/lus'.     From  ehry.salids  which  have  pas,sed  the  winter  then.  i,ateh 
out  in  the  early  days  of  spring  forms  belonging  to  the  variety  ]Va/sf,;i  mu\ 
somewhat    lat('r,  from  tlx.se  whose  d.-n-lopment   lias  been  reiarded'  the 
Ti/amonide,s  f(nms.     Drring  the  early  i  art  of  summer  th,.  WaMuf  f,",rms 
(ii.'out  and  a  little  later  the  Telamnnhhs  also  disappear,  both  forms  pre- 
vioiisly,  however,  .lepositing  ova,  ino.st  of  which  develop  into  larvie  and 
Wuvsahdsand  hatch  out  in  the  later  moi.lhs  (.f  summer  as  the  J/r,,w//?/.» 
fonu.  whose  ova,  again  developing  int.,  ciiry.salids.  pass  the  wiui,-r  in  (hat 
M;ii>'.  and  give  rise  in  the  following  spring  successively  to  the  Wal.shii  and 
hhnnonides  forms.     The  three  varieties  are  evidently  prcMluced  by  influ- 
<'n'(  .s  a..(iug  upon  (he  ehry.salis  and  differing  nceording  to  the  sea.son.  por- 
liiips  iieeording  to  temperature,  whence  the  distiniruisl 


mis  lorm  of  dimorplii.<iin.  which  is  also  said  t 


nguisliing  name  applied  to 
o  occur  in  certain  Spiders. 


603 


INVEliTEBRA TK  MOKPHOLOO  Y. 


i 


1.  Subclass  Apterygota. 

The  members  of  this  subclass  are  all  small  aud  do  not 
possess  wings,  the  absence  of  these  structures  being  a  primi- 
tive feature  and  not  due  to  degeneration  resulting  from  paru- 
sitism  or  other  causes.  In  some  forms  rudiments  of  abdomi- 
nal limbs  are  present  in  the  adults,  and  there  is  no  metu- 
morphosis  in  the  post  embryonic  development  (primary 
ametabolism). 

1.  Order  Thysanura. 

The  Thysanura  or  Bristle-tails  possess  ten  abdominal 
segments,  the  terminal  one  bearing  two-  or  three-jointed  hair- 
like processes,  whence  the  name  applied  to  tlie  order.  The 
body  in  some  forms  (Lepismn)  is  covennl 
with  scalelike  hairs  giving  it  a  s'lvery-gray 
appearance,  but  in  other  ca.^es  these  are 
wanting.  The  antennae  vary  in  length,  l)ut 
are  always  simple  cylindrical  structures, 
the  terminal  joint  in  some  iormH  {Cain p)d('(i) 
bearing  a  peculiar  bilobed  structure  suji- 
posed  to  be  sensory,  and  the  mouth-jjarts 
are  adapted  for  biting  purposes  and  are 
usually  well  developed.  The  first  abdom- 
inal segment  in  some  forms  bears  a  jiair  of 
indistinctly-jointed  a})pendages,  probiihly 
rudimentary  limbs,  and  a  number  of  tho 
succeeding  segments  in  Cumpodcd  bear  spur- 
like processes,  also  suj)posed  to  bo  Hiiilis 
and  recalling  the  8})urs  of  ScolopoKhrlhi, 
especially  as  ])rotrusible  glandular  striic- 
„      „_     ,.  tures,  com[)arable  ijerhaps  to  crural  glands, 

.tuphyiinm     ,aft.r  "'''''"'   "'    "H«ociatiou    With    them    lu    somc. 

LinnocK  from   Hux-    forms. 

'""**  The    nervous    system    shows   but    liitlo 

concentration,  eight  abdominal  ganglia  occurring  in  Lcpisimi, 

and  eyes  are  usually  present,  being  in  some  cases  compoiiiul. 

ri.p  utj;,.,,.tta  vary  in  miml>er,  being  usually  ten,  thougli  in 

Canipodta  they  are  reduced  to  three,  and  the  trachew  in  this 


TYPE  TR  ACHE  ATA. 


503 


same  form  are  interesting  in  being  destitute  of  longitiuliual 
ami  transverse  anastomoses. 

Lepismai.  frequently  found  in  houses,  in  attics  and  similar 

places,  feeding  upon  woollen,  linen,  and  other  fabrics,  but  also 

on  meal  or  sugar.     Campodea  (Fig.  232).  on  the  other  hand,  is 

o  be  found  under  stones  or  dried  leaves  and  is  a  small  white 

torm,  by  no  means  uncommon. 

2.  Order  Collembola. 

_    The  Collembola  are  distinguished  from  the  Thysanura  by 
the  abdomen  consisting  usually  of  but  six  segments,  and  in 
some  cases  the  number  is  even  smaller.     The  body  in  Podura 
IS  covered  with  scales,  and  the  terminal  segment  of  the  body 
IS  usually  provided  with  two  processes  which  may  be  bent  up 
underneath  the  abdomen  and  then  suddenly  extended,  pro^ 
pelling  the  lusect  to  a  considerable  distance.  These  structures 
are  absent  in  the  adult  Anurida,  but  occur  in  young  spec" 
n.ens  and  their  occurrence  and  function  have  suggested  the 
]H>lHilar  name  of  Spring-tails  applied  to  the  order     Neither 
Hbdomiual  appendages  nor  coxal  glands  occur,  but  the  first 
segment  bears  a  peculiar  organ,  having  in  Anurida  the  form 
ol  a  saccular  protrusion,  which  is  probably  adhesive  in  func 
.on      The  antenna  are  usually  short,  and  bear  in  some  fonns 
a.i  antennal  sense-organ  similar  to  that  of   Carnp<xlea ;   the 
.uotith-parts  are  biting,  but  frequently  nnich  reduced  in  size. 
The  nervous  system  is  usually  much  concentrated,  there 
w'th'^M      '"V'"^  postoral  ganglia  situated  in  the 
Hnax     he  abdominal  ganglia  having  evidently  fused   with 
he  last  thoracic.     Simple  eyes  are  presentin  vai/ing  nun.be 
>nt  compound  eyes  never  occur.     A  peculiar  oilman!  ying  1  "^ 
In.ul  the  bases  of  the  antenna,  and  hence  termed  tL  p<I  I 

•Kan.  but  further  information  is  required  concerning  i.. 
l.achea,  are  usually  present,  though  quite  wantingin  Anurida. 
The  genus  Poilura  is  to  be  found,  sometimes  in  consider- 
ahle  numbers  on  the  surface  of  standing  water  in  the  early 
wi-iifi  ..rfjp.r  loruir,  uccui  m  damp  earth  or  und.u-  bark 
^nur^dalH  found  upon  the  seashore  underneath  stones  just 
above  tide-mark.  •' 


'S'fl!^ 


M 


504  INVERTEBRATE  MORPHOLOGY. 


II.  Subclass  Pterygota. 

The  members  of  the  subclass  Pterygota  are,  as  the  name 
indicates,  typically  provided  with  wiugs,  +!  )ugh  iu  a  compar- 
atively few  cases  these  structures  may  have  disappeared 
through  degeneration  due  to  parasitic  habits,  or  through  special 
adaptation  to  certain  conditions  of  life,  as  in  the  neuters  of 
the  Ants  and  Termites.  In  nearly  all  cases  the  larvte  ditlor 
in  form  from  the  adults,  and  various  grades  of  metamorphosis 
are  found. 

1.  Order  Dermaptera. 

The  Dermaptera  or  Earwigs  (Fig.  233)  are  usually  small 
insects   which   resemble   not   a   little    the    Thysanura.     The 
abdomen    terminates   in  a  pair  of   forceplike 
l)rocesses  termed  cerci,  their  shape  suggestiiii,' 
tlie  generic  name  Forjiculn,  applied  to  certaiu 
/f=\  I  N  members  of  the  order.    The  anterior  wings  are 

//lilvS  s'"*ill  ^"^^  chitinous  and  serve  as  covers  for 
the  protection  of  the  posterior  ])air,  which  are 
larger,  membranous  and  veined,  and  when  at 
rest  are  folded  longitudinally  like  a  fan,  and  in 

Fig.  233. -ZaW«    addition  twice  transversely,"  so  that  thev  are 
minor  (.after  Lku-        ,  ,  ^    i    ^      ^  •■,-,■,         , 

n:8).  almost  completely  hulden  by  the  scalelike  an- 

terior pair.  The  antennso  are  long  and  filiform, 
and  the  mouth-parts  adapted  for  biting.  The  Earwigs  are 
terrestrial  forms  and  pass  through  a  gradual  metauiorphosis. 
Iu  many  respects  they  approach  nearer  the  Thysanura  tliau 
any  other  insects,  and  are  related  rather  closely  to  the  suc- 
ceeding order. 

3.  Order  Orthoptera. 

In  this  order,  which  includes  the  Locusts,  Grasshopjicrs, 
iCuloptenius),  Crickets  {Gri/UuM),  CcK-kroaches  {Pcriplaurt^), 
and  other  forms,  the  mouth-})arts  are  adaptcMl  for  biting  and 
the  last  segment  of  the  abdomen  bears  two-jointed  cerci.  The 

TT.iif^.^  xoiiu,  an  xii  tun  iJurniaptera,  covers   iur  tlie 

posterior  pair  and  are  cliitinous  jilates;  the  posterior  ones  are, 


TYPE  TEACHEATA. 


505 


isuallv  small 


on  the  other  hand,  membraiious  and  the  veins  are  for  the 
most  part  arraiiged  longitudiually,  so  that  when  at  rest  the 
wmgs  are  folded  like  a  fan,  though  in  some  forms,  such 'fs 
the  Crickets  m  which  the  anterior  wings  are  short,  a  trans- 
verse fold  also  occurs.  In  the  female  Cockroaches  the  ante- 
nor  wings  are  very  small,  and  the  posterior  ones  wanting,  and 
m  the  ^\  alking  Stick  {IJiapkeromera)--,o  named  from  its  ilsem- 
blance  to  a  green  or  dead  twig-both  pairs  are  entirely  want- 


ing. 


The  antenna,  are  usually  long  and  filiform,  and  the  le-s 
strong  and  adapted  to  a  terrestrial  life,  some  forms,  such  :s 
the  Cockroach,  being  exceedingly  active.  In  the  Grasshop- 
pers, Locusts,  and  Crickets  the  femora  of  the  last  pair  of  le-^s 
are  greatly'  en  arged  and  very  muscular,  serving  hfr  jumping 
while  in    he  Mole-cricket  iOryUotaJpa),  which  burrows  iL  tlfe' 

As  in  the  Earwigs,  the  metamorphosis  is  gradual. 

3.  Oilier  Ephemeridse, 

The  EphemerhhB  or  May-flies  (Fig.  234),  are  characterized 
\n  the  remarkable  brevity  of  their  existence  in  the  imago- 
•stage,  some  forms  existing  but  for  a  few 
hours,  while  others  live  for  several  days, 
the  existence  being  merely  h)ng  enough' 
to  ensure  the  accomplishment  of  the  re- 
productive acts.  The  body  is  elongated 
■md  terminates  in  two  or  three  elongated 
hairlike  cerci,and  on  the  thorjix  there  are 
borne  usually  two  pairs  of  wings,  of  which  /       \ 

tlie  anterior  pair  is  consideral)ly  larger  p,o  oo/  „) 
thau  the  posterior.  The  antei^u.  Le  1:^::!::ZX:, 
short,  and  the  mouth-parts  adapted  for  ^""^• 
I'iting  though  usually  much  reduced,  since  the  imago  takes 
lio  nutrition  during  its  short  existence.  The  first  pair  of  leirs 
IS  usually  slender  and  directed  forward.,  being  of  littlo  -«..a  in 
'"^•'•n'otion.  An  interesting  structural  peculiarity  is  the  oc- 
nnreuce  of  paired  reproductive  ducts  which  open  by  separate 


606 


INVERTEBRATE  MORPHOLOGY. 


pores  instead  of  uniting  as  tliey  do  in  the  majority  of  In- 
sects. 

The  larvse  are  aquatic  and  provided  with  tracheal  bran- 
chise  (see  Fig.  226),  recalling,  except  for  these  structures,  the 
Thysanura.  By  a  series  of  moults  the  adult  stage  is  gradu- 
ally acquired,  the  wings  appearing  in  what  is  termed  the  sul)- 
imago  stage,  a  final  m--  -  ''^jng  nocessary  before  maturity  is 
reached.     The  metam^^-  a  is  thus  incomplete. 

The  genus  Fphemera  is  of  frequent  occurrence  in  the 
neighborhood  of  lakes  and  ponds,  sometimes  occurring  iu 
enormous  numbers. 


>l 


4.  Order  Odonata. 

The  members  of  this  order,  the  Dragon-flies,  are  elongated 
forms  with  two  pairs  of  nearly  equal,  abundantly-veined  winj,'s 
of  usually  large  size,  all  the  forms  being  excellent  fliers  and 
seeking  their  prey  in  the  air.  The  head  is  united  to  the 
thorax  by  a  narrow  stalk  which  permits  extensive  rotation  of 
the  head,  and  the  abdomen,  terminating  in  two  unsegmeuted 
platelike  cerci,  is  long,  and  in  the  large  Dragon-flies,  jEsvhim 
and  Diplax  (Fig.  235),  and  in  the  brightly-colored  Agrio7i  very 
slender,  though  somewhat  stouter  in  the  genus  LihelMa.  Tlie 
anteuntB  are  very  small  and  the  mouth-parts  adapted  for  bitiiip, 
while  the  legs  are  slender,  the  anterior  pair  being  directed 
somewhat  forwards  so  as  to  serve  for  grasping  the  prey. 
The  lateral  compound  eyes  are  very  large,  meeting  on  the 

dorsum  of  the  head,  and 
in  front  of  them  are  situ- 
ated a  pair  of  small  ocelli. 
The  larv8B  are  aquiitic 
and  are  characterized  by 
the  remarkable  develoj)- 
ment  of  the  labium,  wliicli 
is  very  much  enlarged, 
terminating  iu  two  power- 
Fia.  i'in.— Diplax  elisa  (from  Packahd).       £jj|  j^^yj^  j^^j  provided  witli 

a  hiugo,  30  tliat  it  can  be  flexed  so  as  to  lie  beneath  the  In:! ! 
or  suddenly  thrust  out  to  capture  the  unwary  prey.     This 


TYPE  TB A  CHE  ATA. 


507 


apparatus  is  termed  the  "mask."  Respiration  is  carried  on 
by  tracheal  gills,  consisting  in  Agrion  of  three  leaflike  pro 
cesses  situated  at  the  posterior  end  of  the  body,  and  also  by 
the  terminal  portion  of  the  intestine,  into  .vhich  Avater  is 
taken  and  which  is  abundantly  supplied  with  tracheae  The 
water  can  be  forcibly  expelled  from  the  intestine,  serving  to 
l.ropel  the  insect  through  the  water  if  it  so  desires.  The 
metamorphosis  is  incomplete. 


5.  Order  Plecoptera. 

The  Plecoptera,  or  Stone-flies  (Fig.  236),  are  found  in  the 
viciniiy  of  water  and  have  a  somewhat  elongated  body  fre- 
quently  terminating  in  two  long 
cerci  {Perla).  The  antennse  are  long 
and  filiform  and  the  mouth-parts 
adapted  for  biting,  while  the  legs 
are  strong  aud  used  for  walking. 
Two  pairs  of  wings  occur  almost 
e.iual  in  size,  but  lacking  the  com- 
.ucated  venation  found  in  the  Odo- 

liatu,  aud  when  at  rest  lie  fiat  upon  Fig.  236. -Stone  fly,  Perla. 
tiie  abdomen,  completely  concealing  it.  The  larva)  are 
a(iiiatic,  and  are  usually  to  be  found  in  considerable  numbers 
u.i.ler  stones  in  swiftly-runiiing  streams.  Tliey  recall  the 
ili.ysanura  in  their  appearance,  and  possess  tracheal  branchhB 
ou  the  under  surface  of  the  thorax,  which  in  some  forms  are 
retained  m  the  adult.  The  metamorphosis  is  gradual  or  in- 
oomplete  according  as  these  structures  are  or  are  not  retained 
m  tlie  imago. 

G.  Order  Corrodentia. 

The  mmnbers  of  this  group  possess  biting  mouth-parts 
and  are  su.netimes  destitute  of  wings.  The  Termites,  or 
A\  lute  Ants,  live  in  colonies  aud  show  a  ,,olym„rphisin.  TJie 
males  aud  feuiales,  termed  kings  and  queens  (Fj..  237  I  ]}) 
a.v  at  first  provided  with  largo  wings  resembliug  those  of  the 
i  !o<^optera,  but  after  the  maniage  flight  settle  to  the  .n-ouinl 
and  become  wingless.    The  workers  select  from  the  many  pairs 


I 


608 


INVERTEBRATE  MORPHOLOGY. 


one  for  each  nest,  the  remaining  uuselected  ones  soon  dyin<r 
The  neuters  are  of  two  sorts :  tlie  Avorkers  (Fig.  237,  C),  pale  hi 
color  and  with  comparatively  small  heads  and  man'dibles  and 
the  soldiers  (Fig.  237,  D),  in  which  the  head  is  very  large  and 
dark  colored  and  carries  a  pair  of  large  mandibles.  Both 
these  forms  are  destitute  of  eyes,  and  are  to  be  regarded  as  in 
dividuals  which  have  not  passed  beyond  the  larval  stage  bein- 
potentially  either  males  or  females  with  the  reproductive 
organs,  however,  undeveloped.  The  young  larvre  resemble 
Ihysanura  in  their  general  form  and  are  cared  for  and  fed  by 


D 


A  Bo 

Fig.  2^1.—Term<is  lucifuf/us  (from  hKvms) 
A,  winged  male;  B,  female  after  loss  of  wiugs;  C.  worker;  B.  soldier. 


the  workers.     Those   forms  which   are   destined  to   become 
kings  and  queens  are  nursed  for  a  longer  time  than  the  others 
and  progress  further  in  their  development,  being  really  the' 
only  members  of  the  colony  which  reach  the  imago  state 

The  Termites  shun  the  light,  and  the  American  species  are 
chiefly  found  in  rotten  wood,  upon  which  they  feed,  excavatiii- 
burrows  within  it.  In  some  cases  they  prove  very  destructive 
to  the  woodwork  in  houses,  eating  away  the  interior  of  the 
wood  and  leaving  eventually  only  a  thin  shell  in  place  of  the 
originally  solid  beam.  The  African  species  builds  large  clay 
mounds  from  three  to  four  metres  in  lieight,  tunnelled  b^ 


)v  a 


TYPE  TltACHEATA. 


soon  dying. 
7,  C),  jmle  in 
Luilibles,  and 
vy  larjre  and 
ibles.  Both 
,'arded  as  in- 

stage,  being 
•eproductivti 
m  resemble 
•:  and  fed  by 


509 


0,  soldier. 

to    become 
the  otliers, 
really  the 
)  state, 
species  are 
exoavatiiii,' 
lestruetiv(! 
"ior  of  tlio 
ace  of  the 
large  clay 
elled  by  a 


To  tUis  group  belong  also  the  Psocido!  aud  tbe  JUallopham 
T.e  former  are  small  £„„.«  fouu.l  upou  the  leaves  of  vS 
trees  aud  occasiouully  iu  houses.     They  do  uot  show  poly- 
.uorphism  aud  are  usually  provided  with  wings  though  the 
KBuus  Atropos  not  uuoounuou  iu  books  which  have  re,tled 
loug  uuisturbed,   lacks   them.      The   Mallophaga  "n 
des  .tute  of  „,ugs  aud  are  parasitic,  living  upou  tfe  bodL  o 
h mis  (Zto^fe^)  whence  they  are  usually  termed  the  Bi     le 
ll.ey  feed  upou  the  feathers  and  are  comparatively  activeTu 
he„.  movements.      A  tew  forms  occur  on   mammals    eg 
Irwhodectes  on  the  dog,  ""i^is,   e.g. 

.i  J'ml'rr.  °/  f  ""^'  *;™'  '"'''•'''''  "'"  "''""«  --"ovi  i- 
s  ze  and  in  the  absence  of  w.ngs,  aud  the  metamorphosis  is 

K  .a. luai.     Smce  the  Mallophaga  are  destitute  of  wings  Tn  tl  e 

7.  Order  Thysanoptera. 

The  Thysanoptera  are  small  Insects  which  live  upon  the 
leaves  of  various  plants,  which  they  pierce  for  the  puipose  of 
obtammg  nutrition,  and  sometimes  are  very  injuioiis  il 
wheat,  clover  and  other  cultivated  plants.  The  wing  a  e 
u,;.n-ow.  but  imperfectly  veiued,  and  with  the  edges   rin"ed 

a  ting     The  antenna,  are  short  aud  filiform  and  the  mouth 

The  mandibles  are  reduced  to  styletlike  piercing-organs  ami 
re  enclosed  with  n  a  tubular  proboscLs  formed  by  tirfu,1ou 
of  the  abrum  with  the  ma.xilbe  and  labium,  both  !,[  these  1  ° 
|M'pendage.s  retaining  their  palps  an.l  sh„;.ing  usually  tie 
tVlucal  parts      The  legs  are  adapted  for  rapidFocmo  oi  and 
■■e  peculiar  m  that  the  terminal  joint  of  the  tarsus,  iultead  of 
Waring  ungues,  IS  provided  with    a  protrnsible  sac    vh ll 
erves  for  adhesion  ;  on  account  of  this  peculiarity  the  order 
i»  sometimes  known  as  the  I'lnimru^h, 

The  larv.e  e.xcept  for   the 'absence  of  wings   are   closely 


610 


INVERTEBRA TE  MORPHOLOO  T. 


similar  to  the  adults  and  the  metamorphosis  is  gradual, 
though  the  tendency  towards  the  development  of  a  distinct 
pupal  stage  is  shoAvn  by  the  fact  that  the  last  larval  stage 
takes  no  nourishment.  The  genus  Phlceothrips  is  character- 
ized by  the  last  abdominal  segment  being  tubular  in  form, 
while  Thrips  possesses  in  the  female  forms  an  ovipositor  com' 
posed  of  four  valvelike  pieces. 


I!  I 


8.  Order  Rhynchota. 

The  jnembers  of  this  order  are  divisible  into  two  groups 
the  Heteroptera  and  Homoptera,  according  to  the  character  of 
the  anterior  wings.     In  the  Heteroptera,  which  includes  tlie 
majority  of  forms  popularly  known  as  Bugs,  the  basal  partions 
of  the  anterior  wings  are  chitiuous,  while  tlie  tips  are  mem- 
branous, the  posterior  wings  being  entirely  membranous     A 
typical    member  of  this  group  is  tie  common  Squash-bu- 
{Anasa,  Fig.  238,  A),  and  other  examples  are  the  Water-boat" 
man  {Notonecta),  the  large  Water-scorpion  [Belostoma),  and  the 
slender  Water-scorpion  {Bannira),  all  of  which  are  of  frequent 
occurrence  ir  ponds,  swimming  powerfully  beneath  the  water 
by  means  of  tie  flattened  posterior  legs  which  serve  as  oars 
the  anterior  pair  being  directed   forwards  and  serving  for 
grasping   the    prey.     The  Water- measurer    or  Water  -^^^ler 
{Hydrometra)  is  also  very  common  in  ponds,  darting  about 
upon  the  surface  in  search  of  prey,  a  habit  which  also  char- 
acterizes the  genus  Hahhates,  which  lives  upon  the  surface  of 
the  ocean  and  is  found  many  miles  from  land.     Some   mem- 
bers of  the  group  are  entirely  destitute  of  win^s,  as  for  ex- 
ample  the  Bedbug  {Gimex)  and  the  Louse  (Pedicnh,). 

In  th.  Homoptera  the  wings  are  both  membranous,  the 
anterior  pair  being  larger  than  the  posterior,  and,  as  in  tlie 
other  group,  are  sometimes  wanting.  The  Cicada  is  a  member 
ot  tins  group,  as  are  also  the  Aphidse,  or  Plant-lice  (Fig  '^SO 
so  frequent  in  green-houses  and  upon  various  uncultivated 
plants  whose  juices  they  suck,  a  habit  also  shared  bv  the 
near  y-alhed  Coccid.e,  including  the  scale-msects  {Aspkfwfu.s) 
and  the  Mealy-bugs  (Dactylopius),  both  of  frequent  occurrenc", 
on  en.f.iv;ited   plants,  the  former  sometimes  doing  no  little 


TYPE  TRACHEATA.  g^ 

damage  to  apple-trees.     The  remarkable  lieterogony  of  these 
iorms  has  already  been  described  (p.  498} 

In  both  the  suborders  the  mouth-parts  are  adapted  for 
piercing  and   sucking.      The  "^ptea  lor 

Libium  (Fig.  238,  B,  lb)  is 
])rolonged  into  a  slender, 
usually  four-jointed  process, 
grooved  upon  its  upper  sur- 
face, the  groove  being  con- 
vertible into  a  tube  by  the 
closure  over  it  of  the  long 
slender  mandibles  (m)  and 
maxillae  (mx)  which  form  long  ^^^'  ^^^■-^'  ^nasa  tristia;  B,  Mouth- 
slender  needlelike  piercers.  ZroZ)^"^'' "'"""""  '''''"  ^^^"^''^ 
The     antennae     are     usually    ^6  =  labium.  m  =  mandibles 

short    and    filiform,     though    ^*  =  to"g«e-  '?w,  =  maxill* 

:;:;;:;:'  the  Heterop^^a  the,  .a,  be  al.ost  as  I„„«  as 

Many  of  Hie  EhyncLota  are  provided  with  glands  which 
ecrete  an  ofteuszve  fluid,  e.g.  in  Ci,ne.  and  Anala,  and  Tn  the 
Coccda,  wax-glands  are  also  abundantly  present  nroduc  n^ 
;.  secrefon  which  may  cover  the  body  ,rith  wa"n  scaks  "^ 
m  some  cases  form  a  wool-like   mass  covering  the  greater 
part  of  the  abdomen  (PempH,>.).     The  Aphid»  also  posses 
a   a  rule  upon  the  antepenultimate  abdom/nal  segment  pair 
of  tubular  elevations  or  papilte  from  which  a  sweet  secreUon 
«..nes  the  so-called  "Honey-aew,"  which  covers     he  Wes 
ami  stems  of  the  plants  npon  which  the  Insects  live  ZZ 
-gerly  sought  for  by  various  Insects,  more  especL™  by 

The  larv*  of  the  Ehynchota  as  a  rule  resemble  the  aduU, 
even  to  the  .tructure  of  the  ..outh-parts,  anrthe  metam^r 
P  .OS.  .s  consequently  gradual.     'bI Ckada  forms,  I  o leve  " 

mf..ce  of  the  ground  and  living  „,,„„  the  roots  of  tree, 
I  becomes  ransformed  into  a  pupa,  which,  however  con 
t»-es  to  lead  an  active  existence,  becoming  quieslen    ' 


lort  time  before  tlie  moult  which 


only 
results  in  the  formation  of 


512 


INVERTEBRATE  MORPHOLOGY. 


I! :  M 


the  imago,  very  different  iu  appearance  from  the  pupa.     The 
metamorphosis  here  approaches  the  complete  type. 

9.  Order  Coleoptera. 

The  order  Coleoptera  includes  the  Beetles  and  is  richer 
in  s]iecies  than  any  other  order  of  animals.  The  members  of 
the  oup  are  characterized  by  the  anterior  wings  bein^  coii- 
vertetl  into  hard  chitiuous  plates,  the  elytra,  which  cover  iu 
and  protect  the  posterior  membranous  wings  and  the  abdo- 
den,  being  short  only  in  a  few  forms,  such  as  the  Buryiujr. 
beetles  {Necrophorus),  in  which  the  tip  of  the  abdomen  remaiiTs 
exposed,  and  the  Staphylinidae,  or  liove-beetles,  and  /deloc,  in 
which  they  cover  only  the  more  anterior  portions  of  the  ab- 
domen, the  posterior  wings  in  the  last-named  form  beiu^r 
wanting,  as  they  may  also  be  iu  some  of  the  Weevils.  Occa" 
sionally,  as  in  the  Fireflies  {Lampt/rls),  the  elytra  are  but 
slightly  thickened,  and  in  some  forms  they  may  be  completely 
fused  together. 

The  autenn.ne  vary  greatly  iu  shape,  being  usually  filiform 
and  sometimes  very  long,  as  in  the  Boring-beetles  {Monohum. 


Fig.  %'i^.  —  Cotalpa  lanigera  and  its  Lauva  {a)  (from  Packard). 

mils,  Olytus,  Saperda,  etc.),  though  occasionally,  as  iu  tlie 
Lamellicorn  beetles  {JIelolonfha~the  June  Bugs  and  CotaJpa, 
Fig.  239),  the  termiual  joints  are  flattened  aud  folded  together 
like  the  leaves  of  a  book.  The  mouth-parts  (Fig.  225)  are  in 
all  cases  adapted  for  biting,  and  the  legs  for  locomoticm.  Iu 
the  Lady-bugs  {Coccinella)  the  tarsus  consists  of  but  lour 
joints,  one  of  which  is  rudimentary,  while  in  the  Weevils 
(Curculiouida3),  in  wdiich  the  anterior  part  of  the  head  is  pro- 


TYPE  TIUCHEATA. 


S18 


lougecl  into  a  cyl.mliical  s„o„tIike  process  at  the  extremity 
otwnchis    l.e  fflo„th,iuthe  Bori„g.beetle«,  and  iu  tl.e  Po 
Uto-beet  e  (Doryphra)  it  is  forme.l  of  five  joints,  one  of  ^,^t 
»  exceed.n,l3.  .s.uall.     In  otl.er  forms,  such  as  Mdoc  and  the 
-hster-beetles  (Z,«„),  the  tarsi  of  the  two  anterior  pairs  of 
leKs  are  five.j„,nted  and  those  of  tl,e  last  pair  fonr-L  ted 
and  n  others  again,  snch  as  tl,e  Fireflies,  the  Cliclc-beefe 
(tlaternla,)     the    Lamellicornes,    the    Bnrjing-beetles      ml' 

he  Ca,ab  d,e  (U.dosoma,  Cnmhus.  l[arp_du.,  /ijhinns,  etc 
and  the  I,ger.beetles  (CkhuMa).  all  the  tarsi  are  Hve-io  n ted 
and  all  the  j.nnts  approximately  equally  developed. 

Iu  the'l  TJT  '""''  r"'^'  '"  '"""  '"  "'^  "^'ff"-™'  genera. 

lu  the  L„d. bugs  audson.e  other  forms  they  are  Thysanuri- 

..■u,  the  three  anterior  trunk-segu.ents  (corresponding  to  he 

hie  the  abdomen  terminates  in  a  pair  of  cerci.  In  some 
,,ter-beetles  ((?,„„„)  tracheal  gills  are  present,  and  Z 
la  V  e  ot  the  Lamelhcorns  (Fig.  23U.  „)  are  soft-bodied  eyele  ; 
wh.te  h,rms,  characterized  by  a  saclike  dilatation  of  tlie  lasl 
abdommal  se,.nent,  and  live  beneath  the  surface  of  t  e 
K  oum  feeding  up.n  the  roots  of  grasses.  In  the  Click-bet 
t  e.,  (E laternte  the  body  of  the  larva  is  elongated  and  slen- 
.k-    and  very  hard,  these  forms   being  kno™  as  the  wire- 

>1  plants      In  the  Bormg.beetles,  the  larvre,  which  excavate 
"..rows  beneath  the  bark  or  in  the  wood  ^f  various      ee, 
ave    he  l.mbs  almost  or  quite  rudimentary,  while  maggot.' 
like  larvffi  are  characteristic  of  the  Weevils 

The  larva,  whose  life  nnay  be  prolonged  through  several 
■ears,  passes  finally  into  a  resting  p„ pa  stage  of*lhe'Z 
onn,resembhngin  the  body  form  and%he  mouth-part    the 

.HI.  l.o,.oy,  .he  parasite  shp,  „,«>„  L  eg«,  wlnl'Mrcoll."":  1!^ 


614 


INVERTEBRATE  MORPHOLOOT. 


transforms  into  a  maggotlike  second  larva  which  lives  upon  the  honey  on 
the  surface  of  which  it  floats,  and  after  a  time  passes  into  a  resting  pseudo- 
chrysalis  stage,  from  which  a  larva  similar  to  tlie  second  one  emerges,  and 
this  finally  transforms  into  a  pupa  which  gives  rise  to  the  adult. 


m 


10.  Order  Neuroptera. 

The  Neurojjtera  are  characterized  by  the  abundant  and 
rich  venation  of  their  wings,  in  which  numerous  cross-veins 
extend  between  the  longitudinal  ones.  The  mouth-parl.i  are 
adapted  for  biting,  the  mandibles  being  in  some  forms  {Cory, 
dalis)  very  large.  The  lace-winged  flies  {Chrysopa)  also  be- 
long to  this  group,  as  does  also  the  Ant-lion  {Ifyrmeleon,  Fi". 
240),  whose  larva  excavates  a  funnel  in  loose  sand,  and 
buries  itself  at  the  bottom  with  only  the  head  and  powerful 


Fig.  2i0. —Myn)>eleon  obsoletus  (from  Packard). 

mandibles  projecting,  ready  to  snap  up  any  insect  which  s]ii)s 
down  the  yielding  sides  of  the  trap.  The  larvM>  are  usnullv 
Thysanuriform,  those  of  Chri/sopa  attacking  Aphides,  whence 
they  are  frequently  termed  Apliis-lions,  while  tliose  oi  Ci>nj. 
dalis  are  acpiatic  and  possess  tracheal  branchiae  upon  tlu' 
abdomen.  This  larva  is  familiar  to  anglers  as  the  Holl- 
gramite.     The  metamorphosis  is  complete. 

11.  Order  Panorpata. 

This  order  contains  a  small  number  of  forms,  the  majority 
of  which  possess  membranous  wings  reseml)ling  tlios(>  ol'  tlic 
Neuroptera,  except  that  the  cross-veins  are  not  so  numoruiis. 
The  anterior  part  of  the  head  is  produced  into  a  downwaidlv 
projecting  snout,  at  the  extremity  of  whicli  are  the  smail 
biting  mouth-parts,  the  arrangement  recalling  tliat  foum!  in 
the  Curculioniihe  among  the  Coleoptera.     In  the  genus  l'<i. 


TYPE  TRACHEATA. 


515 


buudaut  and 


which  slips 


e  gouus  III. 


norpa,  the  Scorpion-fly.  the  abdomen  terminates  in  a  pair  of 
lorcephke  processes  similar  to  those  of  the  Dermaptera 

The  metamorphosis  is  complete,  the  hirva3  differing  from 
hose  oi  the  orders  already  described  in  possessing  in  addi- 
tion  to  the  three  pairs  of  thoracic  legs  eight  pairs  of  abdom- 
nial  proplike  appendages. 

13.  Order  Trichoptera. 

The  Trichoptera.  also  a  small  order,  inclndes  the  Caddis. 
Hies  {Phryganea,  AnahoUa).  They  possess  two  pairs  of  wings 
the  anterior  pair  nsually  differing  slightly  in  appearance 
from  the  posterior,  which  are  larger  and  folded  when  at  rest 
m  a  tauhke  manner,  the  venation  consisting  principally  of 
.oijgitndmal  veins,  with  bnt  few  transverse  ones.  T)ie  body 
and  the  wings  are  generally  abundantly  covered  with  hairs 
which  in  some  forms  are  scalelike.  The  autennte  are 
usually  l(,ug  nud  filiform,  and  the  mandibles  rudimentary,  the 
maxilhe  and  labium  forming  a  short  sucking  proboscis. 

The  metamorphosis  is  complete,  the  larva)  being  aquatic 
and  provided  with  spinning-glands  with  which  they  bind  to- 
gether  small  twigs  and  particles  of  sand  to  form  cases  within 
which  they  live.  They  possess  tracheal  branchiro  upon  the 
sides  ot  the  abdominal  segments,  and  the  last  segment  bears 
a  pair  of  short  but  stout  processes  which  are  provided  with 
liooks.  The  pupa  is  formed  within  the  larval  case,  but  before 
tiunsforming  into  the  imago  it  leaves  the  case  and  crawls  to 
laud,  where  the  imago  emerges. 

13.  OrtUr  Lepidoptera. 

This  is  a  large  order,  including  the  Butterflies  and  Moths 
all  ..f  which,  with  the  exception  of  the  females  of  a  few  forms 
'^'''W/'f').  possess  two  iiairs  of  wings  covered  with  overlai)piijg 
scalehke  hairs,  and  with  but  few  transverse  veins.  AVhen  at 
i<"st  the  wings  are  rarely  folded,  but  are  eitlier  held  erect,  as 
n.  the  Butterflies,  or  lie  one  ..ver  the  other,  resting  upon  the 
abdomen.     The  body,  like  the  wings,  is  covered  with  hairs  or 


Th 


e   anteunio   differ   considerably  in  shape  in   different 


516 


INVF-^.TEBRATE  MOliPIIOLOQT. 


•t 


s 


^ 


Fig.  241.— Hrad  op  Mdtu. 
Siikinx  lif/iLslri,  showing 


forms,  beiiig  iu  the  Butterflies  usually  club-shaped,  while  iu 
male  moths  they  are  frequently  featherlike,  though  more  si-n. 
ple  or  filiform  iu  the  females.  The  mouth-parts  are  adapt.nl 
for  sucking,  formiug  in  most  cases  a  long  tube,  which,  wheu 
not  in  use,  is  coiled  into  a  helix.  In  the  smaller  members  .)f 
the  group  (Microlepidoptera),  which  are  in  many  respects  the 

most  primitive  and  include  such 
forms  as  the  Clothes-moth  (Tinea), 
the  moth  of  the  Apple-maggot  (Car- 
pocapsa),  the  leaf-rollers  (Pyralidfi'), 
etc.,  the  sucking  arrangement  is  by 
no  means  perfect,  the  mandibles  being 
present,  and  the  maxilhe  and  labium 
resembling  in  structure  the  corre- 
sponding parts  in  biting  insects,  ox- 

-   -     cept    that    the    two    inner    terminul 

MouTiM'AUTs  (after  New-     plates    of   the    labium  are  united  to 

a  ::.  .mteniiai.  *"^'^^  ^    ^^^^^'^    tube.       In  the  higher 

I  =  lai)ruiii.  forms    (Macrolei)idoptera),    however, 

Ip  ^-.  labial  pulp  ;  that  of  the  mandibles  (Fig.  241,  inn)  are  quite 
l.ft  side  removed.  rudimentary  and  the  labium  is  much 
reduced  in  size,  though  its  pulps  iJp) 
are  frequently  large  and  well  d... 
veloped.  The  sucking-tube  is  com- 
posed  of  the  two  maxilho  (m)  which  are  i)roduced  into  two 
long  tilamejits  grooved  on  their  mesal  surfaces,  and  by  their 
ap])oHition  the  tube  is  formed. 

The  metam()r])hosis  is  in  all  cases  complete,  the  larvM' 
being  worinlike  structures  known  as  cat.M-pillars.  Thi^ir 
mouth-pr.rts  are  a.<lapted  for  biting,  and  they  live  for  tUo 
most  part  upon  the  leaves  of  various  plants,  frequently  m'- 
complishing  much  destruction.  This  is 'especially  the"  case 
with  the  Tent-caterpillar  {CJmocnmpa\  which  lives  in  colonies 
enclosed  within  a  web  which  is  extended  from  twig  to  twig  as 
the  leaves  are  gradually  eaten;  various  kinds  ..f  trees  sufl-r- 
ing  from  its  ravages.  The  shade-trees  in  cities,  especially 
the    Horse-chestnut,   are  sometimes   greatly   injured    by  flie 

r .!.,.,. .^K-?n-,rin  yrriiyun,  anil  Un,  iarvH'  of  the 

common  white  Cabbage-butterfly  (/',VnV;  feed  upon  the  leav...s 


m  =  nia.xillie. 
mn  —  iimiidiUie. 
o  =  eye. 


-ped,  while  iu 
gli  more  .si-n. 
3  are  adapt(Hl 
which,  wlieu 
v  members  of 
'  respects  the 
iclude     such 
loth    ( Tinea), 
naggot  (Car- 
i   (Pjralidfc), 
emeiit  is  by 
ndibles  beiim 
3  and  labium 
>    the    corre- 
,'  insects,  ox- 
ler    teriniuiil 
re  united  to 
I  the  higher 
i),    however, 
m)  are  quite 
um  is  nnu'li 
ts  pulps  (//)) 
id    well    (Ic- 
ube  is  coiii- 
!ed  into  two 
nd  by  their 

I,  the   hirvii' 
irs.      Thi'ir 


TYPE  TR ACHE  ATA.  5^7 

of  the   Cabbage;    many   other  similar  examples   might  be 
given      A  few  of  the  Microlepidoptera  possess  aquatic'lal^ 
).utthey    orm  exceptions.     In  the  typical  cateiillar  the^ 
are,  in  addition  to  the  three  pairs  of  thoracic  legs,  Le  pa    s  of 
•short  stout  prop-legs  situated  upon  the   third,  fourt  lifi  th 
s.xth,  and  tenth  abdominal  segments,  and  the  body  may  be 
covered  with  hairs  of  various  lengths,  as  in  the  larvafof  nnn' 
-oths   (e.g.   the  Woolly  Bear,    Spilosonu,),    or   may   possZ 
spiny  processes,  as  in  the  larvae  of  the  Mourning-cloak  Butter 
%    {Vanessa)    which    feeds    on    the   Willow, ''or    v.dou    l" 
shaped   tubercles,  as  in  the  American  silkworm  iTelea).^ 
e  ^o.op.a   arva.     In  one  group  of  moths,  the  Geome tril 
bu    two  or  three  pairs  of  prop-legs  occur,  situated  on    tlfe 

oe    postei-ior   segments,    and   in    progression   these  for 
ai  uv  these  legs  up  close  to  the  thoracic  limbs,  throwing  tl  e 
intervening  portion  of  the  body  into  a  loop,  whlnce  the  ten  s 
measuring-worms"   or    "loopers"   often  applied   to     1.17 
rare    cases,  as   in   a   few   Microlepidopteri,  the   lai        s 
iviHiout  feet  ami  luaKKotlike.  ""v.iis 

The  i,„p,.  „,.  ohi-ysulis  is  of  the  ohMa  variety,  au.l  i,  f™ 
<iue.ty  e„cIo.e,l  withi,,  a  sill<eu  case  tenned'the  „o„  .t 
»l..>n  bythe  larva  whose  salivary  glau.ls  are  couverte  iu to 
>!  mm„K-«lau,ls.  A  ceoou  is  „„,re  Renerallv  present  i/tl 
Moths  than  ,n  the  B„ttorllies,  whose  chrysali.fs  Lre  snspen.ed 
.V  a  patch  of  silk  to  which  the  hin.l  en,l  of  the  p„  a  is  I 
tadiecl  or  may  be  in  acljition  slnn.-  in  .,  sille,,  1  „  ■ 

ro..n,l  the  body  near  the  nml.lle  (Kg.  Lii)  ""'"'' 

14.  Order  Kymenoptera. 
The  Hymenoptera  possess  fonr  membranous  wings  with 
"mparatn-ely  few  veins  and  not  covered  with  scah-s  ^r  ,m 

.  pos  enor.  The  al  d.m.en  is  sometimes  l,roa,Ily  attached 
lo  thorax  as  „,  the  Saw-flies  (Tenthredinida,),bnt  r" 
-  ally  the  anterior  one  (Bees)  or  two  (Ants)  abdo  ninal  s el . 
N..;..t»  are  very  narrow,  so  tl„>t  the  al„lon,en  Meen.s  to  CL 
-..".'"  by  a  stalk.  The  fenndes  possess  ovipositors  which 
-,■  be  retractile  and  provide.l  with  a  poison^iand,  fo™,-  '! 


518 


INVERTEBRATE  MORPHOLOGY. 


If  1 


mjcp 


efficient  organs  of  offence  and  defence,  as  in  tlie  Ants,  Bees, 
and  Wasps,  or  else  long  and  slender  and  but  partially  retrac- 
tile and  destitute  of  a  poison-gland,  as  in  the  Saw-flies,  Gull- 
flies,  and  IchueumonidsB. 

The  mouth-parts  are  adapted  partly  for  biting  and  partly 

for  licking.  The  mandibles  (Fig.  242, 
mn)  are  well  developed  and  fitted  for 
biting  in  all  forms,  and  in  the  Teu- 
thredinidse  the  maxilloe  are  also  like 
those  of  biting  insects,  while  the 
inner  of  the  two  terminal  plates  of 
the  labium  are  united  to  form  a  tube, 
the  outer  plates  remaining  separate. 
In  the  Bees  and  Wasps  the  maxilhe 
{inx)  become  elongated  and  are  uo 
longer  adapted  for  biting,  and  the 
inner  terminal  plates  of  the  labium 
are  fused  together  to  form  a  luiij; 
touguelike  structure,  the  glossa  [I), 
the  outer  plates  forming  what  are 
termed  the  paraglossae  ( pg).  The 
entire  apparatus  is  adapted  for  biting 
aud  also  for  licking  up  the  huiiej 
contained  in  the  nectaries  of  flowers. 
The  great  majority  of  forms  are 
solitary,  but  a  few  Bees  {^pis,  Bom- 
hits)  and  Was])S  {Vespa,  Sphex)  and  the  Ants  [Formioi, 
Camponohis)  form  social  aggregations  with  more  or  less 
pronounced  polymor})hism,  to  which  reference  has  already 
been  made.  The  Gall-flies  {Cynips)  lay  their  eggs  upon  the 
leaves  or  stems  of  plants,  at  the  same  time  injecting  a  jxiisou 
which  causes  a  proliferation  of  the  plant-tissues,  forming'  ;i 
gall  in  the  interior  of  which  is  the  larva  of  the  insect ;  while 
many  forms,  such  as  the  Ichneumon-flies,  Proctotrupes,  Ptero- 
malm,  Microgtister,  etc.,  are  parasi<^ic  in  their  larval  stago,  the 
eggs  being  deposited  in  or  xipon  the  bodies  of  the  larNicnf 
other  insects,  a  very  decided  cluv'k  being  exerted  U])oii  tin' 
larvio  of  injuriouH  insects,  such  as  the  Cabbage-butterfly,  h.v 
these  forms. 


Pig.  243.  — MouTH-rAUTB  of 
Bee,     Anthophora     (after 
Newport  rroin  Gbggnbaur). 
I  —  glossii. 
Ip  =  labial  palp. 
mn  =  mandible. 
mx  =  maxilla. 
mxp  =  maxillary  palp. 
pg  =  paruglossa. 


TYPE  TRACHEATA. 


619 


lie  Ants,  Bees, 
irtially  retrac- 
^aw-flies,  Gull- 


The  lar™  of  the  Tenthredinida,,  for  example  that  of  the 
Poar.sl„g  (&fa»J«,),  „hi„h  feeds  upon  the  leaves  of  the  pear 
ue    resemble   the  caterpillars   iu  possessing  prop-wf  o 

forms,  however,  owing  to  parasitise,  or  to  being  in  contec 


Pig.  343.-<SMea,  ichneumonea  (from  i-ackard). 


Fm   244.— ;7^;,o<?«rwa  Aom  (from  Packard) 
^vlth  au  abundant  supply  of  nutrition  stored  up  by  the  parents 
I^-s,  Wasps)  or  to  bein,.  fed  and  cared  for  b/the  woZl 

"tnely  destitute  of  le^^s.     The  metamorphosis  is  comulc 
the  pitpa  being  a  pupa  lifn'ra.  complc-.. 

IT).  Order  Diptera. 

Pm!lt"!Fir'i«V%''"',  '■"■""  .""""'te^.  !"■'  two  wing,  are 
paseat  (l.g,  2«>,  which  ar„  those  of   the  mesothorar,  the 


620 


INVERTEBRATE  MORPHOLOGY. 


metathoracic  pair  being  usually  represented  by  a  pair  of  club- 
shaped  bodies  on  the  sides  of  the  segment,  termed  hcdteres  or 

balancers.  The  wings  are  always  trans- 
parent and  the  veins  by  no  means 
abundant.  In  a  few  forms,  such  as  the 
Sheep-tick  (Melophagus)  and  the  Flejis 
{Ihdex),  the  wings  are  entirely  wanting,' 
in  harmony  with  the  parasitic  habits 
which  these  forms  possess,  but  they 
form  exceptions  to  the  general  rule. 

The  mouth-parts  are  adapted  for 
sucking  and  also  for  piercing;  the 
labruxn  (Fig.  245,  Ir)  and  labium  {la) 
are  prolonged  into  grooved  processes, 
forming  together  a  tube  within  which 
lie,  in  the  female  Mosquitoes  (Oulex) 
and  Gadflies  (Tabanus),  two  pairs  of 
elongated  needlelike  rods  which  repre- 
sent the  mandibles  (md)  and  maxillio 
(mx),  to  which  a  lifth  unpaired  stylet 
may  be  added  which  arises  as  a  growth 
from  the  lower  wall  of  the  pharynx 
{hy).  In  other  forms  the  maxillae  only 
OF  A  Gnat,  Culex,  the  ^^^.ve  the  ucicular  form,  the  mandibles 
Labrum  turned  to  fusing  with  the  labrum,  and  in  all  cases 
ONE   SIDE  (fro,u  h.ht-  the  maxillary  palps  are  present,  whil,> 

the  labial  palps  are  undeveloped,  lu 
the  ordinary  House-fly  (Mtisca)  the  ex- 
tremity of  the  sucking-tube  is  expanded 
into  a  disklike  structure,  and  in  all 
forms  the  salivary  glands  open  near  the 
extremity  of  the  tube, 
usually  niaggotlike  (Fig.  244),  entirely 
destitute  of  feet,  and  in  some  forms  the  head  even  is  indis- 
tinguishable. The  metamorphosis  is  complete,  the  pupa  boiiig 
in  the  Mosquitoes  active,  swimming  about  in  water,  thou^^h 
more  usually  it  is  incapable  of  motion,  and  enclosed  witliiu 
the  last  larval  skin,  thus  belonging  to  the  coarctata  variety. 


Fig.  245.— Mouth-parts 


WIG) 

hy  =  hypopharyux,       a 
process  of  labium. 
I'i  =  liibiuin. 
Ir  =  labium. 
md  —  mandible. 
7IU  --=  maxilla). 
p  —  maxilliiry  palp. 
The    larva)    are 


TYPE  TR ACHE  AT  A. 


031 


^^^^iopment  and  Affinities  of  the  Imeofn      Th.       i     . 
dovelopment  cannot  be  discussed   11.  ^^^y  stages  of  Insect 

books  of  Embryology,  but  ^2'        ^Id  Se  7n    '"'"l^  *^  *^^^- 
uoinenou  which  occurs  duriue  the  IZf        1  ^  *"  remarkable  phe- 

nnaginal  conditions  in  tl^Xm     '^7'"  """^  '''' ^""^^^  '^  ^he 
describing  the  developme  t  o  ^ A^^^^^^^^^^^  "  ""''''"     '" 

the  transition  from  one  sta^eto   hVn     /     .  ^""'"^"'^  ''"*  ^^^'-^^  ^"^''^g 

e-tion  of  certain  parL  ^^^^21:^^2  7\  ^"'"^""^  '■^^'^"- 
tl.o  same  process  occurs  durinr  he  Z     ^  ^"  ^^'f  ^'o'^metabolic  Insects 

t'.o  majority  of  the  muscle  ad'  t  e  S^difl  "\'""^  '^^P^^^'™'^' 
<ia-es  undergoing  defeneration   nn^  T         f^'^^^ive  tract  and  its  appen- 

«^lood.corpus:ies,'theirrgrmer;^  f^f  'T''  ''^'^ 

i"the  larva  and  known  as  m^.V^aT    ;1^^^^ 

fon  proceed  ;.«n>«...,,  so  that  ti,e  idem  t'v  of  tl.  v  ''''  '°'  ''^'°"•^^- 
scrved  throughout  the  process.  The  im  1  fal  d  ^'^"°'^\«''g^n«  ^^  Pro- 
portions of  the  original  anla-^en  o?  Zl  ''''  '^  ^'  '^^^^^ed  as 

rained  during  larvanifeir.!:r:b;onL"Sn"^^^^^     ""^'  '''"^  '^■ 

be  N^t  :tt  :r;^r  :rrc:^^.:^^^^  r-r-  ^^  '-- 

eates  a  descent  from  Apterygote  ance  or  !nd  ^^"^""5  "^'"^  '''"'*  ■"^"- 
larva.  of  a  wormlike  ot  maLtUke  form  r  T  ''"^'''  ''^'''^'  P''^^*^-^' 
highly  specialized.     It  is  Tn  thes.^^^^  I"  ''"  probability  the  most 

occurs,  and  it  is  selJl::drnt        t   r^-  d  .?:n:r^'''^^^  ?^^^""^^^ 
i;l.o.ses  are  more  primitive  than  the      nf,  i^    '^^  uITT'I  "^''^'"«^- 
•icponds  upon  the  differences  in  habit  and  stn  ctu    tf  the  b  '"''''^''^'^^'^^ 
and  becomes  more  and  more  conn.tpt.  o„       '.''^"'^  "^  ^he  larva  and  imago, 
•Icpart  more  and  u^oreZL^r^l^^^^^^  V  ''''''  "'^^  ''"'^«'"«« 

Consequently  it  may  be  cone  udnh^tnorf""'™  ''^'  ''  ^^^^^^ure. 
which  retain  most  perfectly  Zh  1^1.  "I' "''  '^''  "^°«^  ^''^^'^^^ 

elnu-acters.     These  L  ^l^" ^^XiX^"^''  ^"^  "'^'"'^""''''^ 
both  in  the  adult  and  larval  stages'  t.  Cor    d^iiarT''^ 
not  become  modified  by  parasitism)  a    1  tlw   n  h     /      ^'  '"  ^^'^  ^'^'^ 
•'^^f,-,d  it  is  intorestL^otri;^st.^  cZZu?"  ''T'' '- 

•-r g^^;';;j-~-  -  -  -r  r ^-- - 

...o^rr  :;S:rtJ-rtS --;;;:-  r-s  in  the  .rv. 
f"">'naptera,  is  that  of  the  Thysa.m  terfwh        i  '"'"  ''^"'"  ^^^  *''« 

'""i"Hte  affinities  with  the  R  Stf  t  L     7     '     '  "°^  °^«»th-parts 
'^  --d  group  t^ceable  back  tr^ ^im^ P^^^:  ''''''''  ^-"^"« 

;je  resemblances  l^i.^ll^Za':^:::;:^^-:'^  T""''''^ 
^^-  character  of  the  wings  and  by  the  mouth^arts."";::  .l!:  I^;^' ;^ 


622 


INVERTEBRATE  MORPHOLOGY. 


^\ 


lated  are  the  Neuroptera  with  Thysanuriform  larvae,  probably  to  be  re- 
garded as  a  group  which  has  undergone  a  development  parallel  to  that  of 
the  Ephemeridae  and  Odonata,  the  relationship  bei.ig  traceable  back  to  an 
ancestor  common  to  it  and  the  Ephemeridae.  To  this  group  may  also  bo 
referred  the  Plecoptera. 

A  fourth  group  includes  those  forms  in  which  the  larvfB  are  provided 
with  prop-logs,  secondary  forms  in  which  all  indications  of  the  Thysanurid 
ancestors  have  disappeared.  Of  such  forms  the  Panorpata  show  relation- 
ships on  the  one  hand  with  the  Ephemerid  group,  and  somewhat  closely 
related  are  the  Trichoptera,  whose  entire  organization  points  to  a  close 
affinity  with  the  Microlepidoptera.  From  the  primitive  Microlepidoijter-i 
two  lines  of  descent  are  probably  to  be  traced,  one  leading  to  the  Maero'- 
lepidoptera  and  the  other  to  the  primitive  Hyraenoptera,  the  resemblance 
between  the  larvae  and  the  mouth-parts  of  the  Tenthredinid*,  and  these 
of  the  Microlepidoptera  being  very  striking. 

The  two  remaining  orders,  the  Coleoptera  and  Diptera,  are  very  hi-rhiy 
specialized,  both  being  holometabolic,  and  the  temptation  is  to  look"  for 
their  ancestors  in  forms  with  a  similar  metamorphosis.    This  tempfuiou 
may  be  justified  in  the  case  of  the  Diptera,   whose  larva  are  the  most 
modified  of  all,  and  it  is  not  impossible  that  they  hnve  descended  from 
primitive  Hymenopteran  ancestors,  their  nearest  existing  relatives  beiii- 
the  Tenthredinidae,  whose  sluglike  larvae,  suggest  not  a  little  the  k-i.s't 
modihed  Dipteran  maggots.     With  the  Coleoptera,  however,  the  case'is 
different,  and  it  seems  more  probable  that  their  holometabolisin  has  l.,.,-n 
acquired  quite  independently  of  that  of  the  other  holometabolic  orders 
The  larvae  of  some  beetles,  notably  those  of  the  Coocinellid*,  are  markclly 
Thysanuriform,  and  prop-legs  do  not  occur  in  the  order.    To  which  of  the 
groups  they  are  to  be  referred  it  is  very  difficult  to  say,  though  the  mouth 
parts  and  the  arrangement  and  structure  of  the  wings  in  the  adults  point 
to  an  affinity  witli  the  Orthoptera. 

Granting  a  descent  of  the  Pterygota  from  wingless  ancestors,  it  boco.nos 
an  interesting  problem  to  discover  the  origin  of  the  wings.    Attempts  have 
been  made  to  show  that  they  are  modified  tracheal  branchias  a  theory 
which  necessitates  tiie  derivation  of  the  Pterygota  from  aquatic  ancestors 
bucli  a  derivation,  however,  is  unsupported  by  any  evidence  at  pivsnK  af 
our  disposal,  it  being  much  more  probable  that  the  immediate  ancestors  of 
the  Pterygota  wore  terrestrial,  just  as  Campodea  is  to-day.     The  wiix's 
arise  in  the  emt^ryo  as  dorsal  outpouchings  of  the  meso-  and  metathora'x, 
traeliea3  later  pushing  out  into  them,  and  transient  indicaiions  of  o„t- 
pouchings  of  the  prothorax  also  occur  in  some  embryos.     It  has  been  s,,,.- 
gcsted  that  primarily  the  wings  were  platelike  outgrowths  of  the  thoracic 
seginents  which  served  to  break  the  fall  and  increased  the  distance  irav- 
ers.'d  by  jumping  Insects,  and  in  support  of  this  view  tiie  fact  n.av  he 
mentioned  that  many  Apterygota  are  saltatorial.     The  limitation  ..f'  ihc 
wings  to  the  meso-  and  metuthorax  may  stand  in  some  rnlutinn  („  the 
centre  of  gravity  of  the  body. 


TYPE  THACIIEATA.  ^^3 

The  Phylogeny  of  the  Trachentn     if  t.      u 
together  the  Crustacea,  Araor^r:^^  ^X   ^  •'''  ^"^^''^  *«  "-*« 
Arthropoaa^  characterized  by  iX^^.^^'^T ^l^ ''''^''  ^^'«"P'  ^^e 
-ourrence  of  jointed  limbs,  and  by  Te Ts  ,1  '"""'  '""''•^'  ^^  "'« 

i"nb,s;  and  furthermore  it  ms  been  cuVZ  "'^  ^'^^"'  ^*^'"S  °'«d'fied 
-"1  the  Tracheata  as  closely  related  '"fr^^^/^  ««"«ider  the  Arachnida 
..oup.  of  trachea.     The  eiriy  ^oc     ^  oT'^^^^^^ 

groups  also  show  many  points  of  sinXTtvH  'fP™'"*  in  the  three 
«i.ows  decided  differences  in  the  deTa  Is  h1^^-^  ^  '''''''  examinaUoa 
'"ay  have  operated  to  produce  the  Z?.i.-  '''  ^""^^'•gent  evolution 

-'i  it  can  be  settled  only  by  a  onsZit  '';',;''  P^*^'^^"^  *°  ^«  ^^^tled" 
winch  indicate  the  phyloger.;  of  t'  e  v  '"  "'"  '"^^«  ^^  «"^  <^i«Posa 

wouM  prove  entirei;be'yofd[h:'limL^^^^^r^  ^^^^ 

to  ^^St  r  r  ^  -  "tirfP^^  -  -  Crustacea  is 
descended  trom  ^-..P^^ll  Ice  a^^^^^^^^^^^^  '^-e  in  all  probability 

;n  the,r  affinities.    Are  the  Tracheair  then  «        T'-^^^^t^'^'y  Crustacean 
aeea  and  from  forms  which  poLesl  tel^V  O^ '''  '""  '''  ^-- 
of  the  group  negatives  any  such  sunnnJn       t  "^  P'"^^^'^*  knowledge 

Tracheata  should,  like  the^p.^er^rv    de^^^^^ 

ancestors  ;  it  must  rather  be  conceded  that   h         •  f'"^  ^'-^i'^-^.-like 
and  the  Arachnida  are  due  to  conterln?"  *'^^^''°•'^^'ties  between  them 
ant.es  to  the  acquisition  of  comraSv  I^        "'  *'"  ^'"^'•^'^"'«  «•'«'• 
he  ova,  distributed  in  a  similar  mannri'T  """T'  ^'  '"^^'y^'^  ^« 
to  the  exigencies  of  a  terrestrial  TiJe     11^0         '""''^""^^  of  the  adult 
groups  seems  at  first  an  importan   noinlof       T"''  ^^  ''''^''^  *"  both 
only  by  a  community  of  descent  butl        ""^^""'^  *^  '^«  «««o»»ted  for 
terrestrial  Isopoda  trache^  So  ocL  'i^  u"  br  "  r?''^"'^  ^^^'  -  ^^e 
their  occurrence  in  these  forms  ranireW.         ,""'  "P'^^*^"'^'  ^"^  that 
anyphylogenetic  significance,  i    ievidenf   hTf."^  "'''^P^""°"'  ^'thout 
catjons  of  affinity  is  much  reduc  d     It    'I  J    T  "^^P^-^^nce  as  indi- 

Malpighiantubulesof  theArachnidaandcrul  '  P''"*'^^  '^"^  ^''^^  ^he 

-e  X.eheata  they  are  eetoder^rS:^— ^1:;:^— 

-  Ariidl;^"^^^  .  closely  related  to 

«o  that  the  conclusion  seems  inevitable  '1?"^^'''^''  f  '''''  P'-^no^nced, 
nvo,l  from  Annelid-forms  and  hav.   h     f         Tracheata  have  been  de 
{-dent  of  that  of  the  J^^^^ ^^^  ^^  P"^'«^-y  P-tically  indt 
Id  ancestors  of  Peripatus  and  those  of  If.; n   V'"''^'  '^'''  ^^^  ^"ne- 
«losely  related,  and  that  certain  of  1  p''»«tacea  were  more  or  less 

^-'Ps  are  thus  to  be  acco'^^/fL    t^S"  ^'T'*"'"^«  ^^  ^»  '^^  *h- 
P'-e^-'nt  ,„  a  position  to  judge      One'r  o  n  T''^*  '^*^"*  ^'«  ^^^  "ot  at 

pound  eyes  of  similar  stn.cf.  re  ^l^l^r    ''  "'^  "««"--ce  of  com- 
tion,  sine«  it  --^ «     ■  "  groups,  seems  w^-thv  -f  --     -^ 


624 


INVERTEBRA  TE  MOBPHOLOQ  T. 


\\t 


markable  instance  of  convergent  evolution.  It  is  to  be  noticed  that  tlm 
most  primitive  Insects,  the  forms  througn  which  affinities  +o  the  Crustiicoa 
if  they  exist  must  be  traced,  are  as  a  rule  provided  only  with  simple  eyes, 
a  condition  repeated  in  the  eyes  of  Insect  larvae — a  fact  which  indicates  tluit 
the  compound  eyes  are  structures  which  were  not  characteristic  of  tlie 
primitive  Insects,  but  have  developed  within  the  limits  of  the  group  aiid 
can  therefore  have  no  phyletic  connection  with  the  compound  eyes  of  the 
Crustacea.  Adding  to  this  fact  the  independently-developed  tendency  to 
form  compound  eyes  seen  in  certain  Annelida  and  Pelecypod  Mollusks,  it 
seems  probable  that  notwithstanding  their  remarkable  structural  siinilaii- 
ties  the  compound  eyes  of  Crustacea  and  Insects  have  been  independently 
acquired.  Instead,  therefore,  of  uniting  the  three  groups  together  as  a  typo 
Arthroprda  equivalent  to  the  other  types,  it  seems  preferable  to  separate 
them  as  distinct,  just  as  is  done  with  the  Annelida  and  Mollusca,  and  the 
Annelida  and  Prosopygia. 

Starting,  then,  with  the  supposition  that  PeripaUis  has  descended  from 
Annelid  ancestors  and  represents  the  ancestors  of  the  Myriapoda,  the  rela- 
tionships of  the  various  orders  of  this  class  and  of  the  Insects  remains  to 
be  traced.  Unfortunately  a  large  gap  exists  between  Peripatus  and  any 
recent  Myriapods,  and  it  is  possible  that  this  class  is  a  heterogeneous  group ; 
indeed  oy  some  recent  authors  it  has  been  sugj^ested  that  it  should  be 
done  away  with  as  a  class,  the  Chilopods  being  united  with  the  Insecta  to 
form  one  class,  while  the  Diplopods  (perhaps  witl;  the  Pauropoda  associated 
with  them)  should  form  a  second.  There  is  no  doubt  but  that  Peripatus 
possesses  many  tracheate  peculiarities,  but  its  affinities  to  the  remaining 
Tracheates  are  much  more  remote  than  those  which  exist  between  the  vari- 
ous groups  of  Myriapoda,  or  between  any  of  the.w  groups  and  the  Insecta. 
The  character  of  the  various  appendages  considered  in  relation  with  the 
nervous  system  seems  to  afford  an  admirable  means  of  indica'  "ng  the  rela- 
tionships of  the  various  groups.  The  brain  of  Peripatus  seems  to  be 
formed  by  the  fusion  of  three  pairs  of  ganglia  ;  the  most  anterior  and  dor- 
sal of  these  gives  rise  to  the  antennal  nerve  and  the  most  posterior  inner- 
vates the  mandibles,  while  upon  the  middle  one,  which  is  closely  related  to 
the  mandibular  ganglion,  the  eye  seems  to  be  placed.  It  may  be  assumed 
that  the  ganglia  with  which  the  e}-es  are  associated  represent  the  Annelid 
supraffisophageal  or  cerebral  ganglia  and  may  therefore  be  termed  the  jiro- 
tocerebrura,  while  the  antennary  ganglia  form  the  deu.,ocerebrum,  and  tlie 
mandibular  the  tritocerebrum.  In  the  Myriapods  and  Insects  the  brain  is 
also  composed  of  three  parts  to  which  the  same  names  are  applied,  tlio 
antennae  being  innervated  from  the  deutocerebrum,  while  the  tritocerebrum 
lacks  a  corresponding  appendage,  though  in  certain  Insects  transient  indi- 
cations of  a  tritocerebral  appendage  have  been  seen.  Bearing  these  facts 
in  mind,  the  ganglia  and  appendages  of  the  various  groups  may  thus  be 
tabulated,  and  to  make  the  comparison  complete  the  Crustacea  are  also  in- 
cluded. 


f 


TYPE  TRACHEATA. 


526 


Ganglion. 

Crustacea. 

Peripatus. 

Diplopoda. 

Chilopoda. 

Inseet/i. 

Deutocare- 

hral. 
Tritiicere- 

bral. 
Ist  postoral 
•Jd        " 
3.1 

nh     " 
.5th      " 
6th       " 

Antennules 
Antennae 
Mandibles 
Ist  maxillae 

ad 

Ist  thoracic  limb 
ad       " 

Antennae  ? 

Mandibles 
Oral  papillae 
1st  legs 
2d     '• 
3d     " 
4th   " 
6th  " 

Antennae 

Antennae 

Antennae 

Mandibles 
Maxillae 
Ist  legs 
ad     " 
3d     " 
4th   " 

Mandibles 
Is   maxillae 
2d 

Maxillipedes 
1st  legs 
3d     " 

Mandibles 
1st  maxillae 
ad       " 
1st  legs 
2d     " 
8d     " 

;ea  are  also  in- 


It  will  be  seen  from  this  that  in  the  Diplopoda  the  arrangement  is 
intermediate  between  that  found  in  Peripatus  md  that  of  ihe  Chilopoda 
while  these  latter  approach  closely  the  Insecta,  and  this  seems  to  be  the  ac- 
tual relationship,  Scolopendrella  forming  an  intermediate  link  between  the 
Chilopods  and  the  Insecta,  approaching  the  Thysanura  closely  in  the  ar- 
rangement of  the  mouth-parts  and  in  the  number  of  segments  of  which  the 
body  is  composed.     The  Diplopoda,  it  is  true,  pass  through  a  larval  stage  in 
which  but  SIX  legs  are  present,  and  it  might  at  first  sight  be  supposed  that 
this  indicates  an  affinity  with  the  Insecta,  but  these  legs  do  not  belong  to 
the  .same  segments  as  do  those  of  the  Insects,  and  furthermore  the  occur- 
rence of  rudimentary  abdominal  appendages  in  some  Thysanura,  as  well  as 
111  the  embryonic  stages  of  probably  all  Pterygota,  indicates  that  the  In- 
secta have  been  derived  immediately  from  forms  with  many  pairs  of  appen- 
dages, and  these  forms  seem  to  be  represented  most  accurately  by  the  exist- 
ing Scolopendrella. 

SUBKINGDOM  METAZOA. 

TYPE   TRACHEATA. 

I.  Class  Protracheata. -Annelid-like  forms  ;  trunk  not  differentiated 

into  thorax  and  abdomen  ;  w  ith  nephridia.     Peripatus 
II.  Class  Myriapoda. -Elongated  forms;   trunk  not  differentiated  into 
thorjix  and  abdomen  ;    posterior  trunk-segments  with  appen- 
dages in  the  adult. 

1.  Order  Pauropoda. -^m^W  forms  ;  with  only  one  pair  of  maxillje  • 

antenn*  ending  in  three  flagella  ;  reproductive  orifices  at  basi,s 
of  third  pair  of  trunk-appemlag.'s.    Pauropus,  Eurypauropns 

2.  Order  Diplopoda.-Wnh   only  one   pair  of   maxill*  :    antennae 

simple  ;  reproductive  orifice  on  .second  or  ),etweeu  second  and 
third  truiik-segmonts ;  mo.st  of  the  trunk-.segments  with  two 
pairs  of  legs.  luhm,  Lysiopetalum,  Polydesmus,  Strow/vlo- 
soma,  Glomeris. 

3.  Order  Chil»poda.-W ith  two  pairsof  maxilla;  and  with  maxillipeds- 

antenn*  simple;  reproductive  orifice  on  the  antepenultimate 
segment:  each  tr!,!,k-sec.n3ent  with  a  single  pair  of  legs. 
Qeqphilus,  Scolopendra,  LitUobiun,  JScutigera. 


11 


526 


IN VEKTEBUA TE  MORPHOLOQ T. 


m 


4.  Order  Symphyla. —Vfith  only  one  pair  of  maxillEo  and  no  maxilli- 
peds ;  antenme  simple ;    most  of  the  trunk-segments  with  u 
single  pair  of  legs.     Scolopendrella. 
III.  Class  Insecta. — Trunk  differentiated  into  thorax  coniposea  of  throe 
rings  and  an  abdomen  with  typically  ten  segments. 

1.  SubcUiss  Apterygota.—T\\ov&.x  without  wings;  abdominal  segments 

sometimes  with  rudimentary  limbs  in  the  adult. 

1.  Order  Thysanura. — Abdomen  with  ten  segments,  bearing  two  or 

three  cerci ;  abdominal  appendages  frequently  present.  Le- 
pisma,  Campodea. 

2.  Order  Collembola. — Abdomen  with  six  segments  terminating  in 

two  springing-orgaus  ;  abdominal  appendages  wanting.  Fodura, 
Anurida. 

2.  Subclass  Pterygota. — "With  usually  two  pairs  of  wings  situated  on 

the  meso-  and  nietathoracic  segments ;  abdominal  appendages 
wanting  in  adults. 

1.  Order  Dermaptera.—KhAomQn.  with  forceplike  cerci ;    anterior 

wings  small  and  chitinous,  posterior  folded  like  a  fan  and  also 
transversely;  mouth-parts  biting;  metamorphosis  gradual. 
Forjicula,  Labia. 

2.  Order  Orthoptera. — Abdomen  usually  with  cerci  ;  anterior  wings 

chitinous,  covering  the  posterior,  which  fold  fanlike  and  some- 
times also  transversely  ;  mouth-parts  biting  ;  metamorphosis 
gradual.  Caloptenus,  Gryllus,  Qryllotalpa,  Periplaneta,  Dia- 
pheromera. 

3.  Order  Ephemeridce. — Abdomen  with  two  long  cerci ;  wings  mem- 

branous and  richly  veined,  the  anterior  larger ;  not  folded  when 
at  rest ;  mouth-parts  biting,  but  reduced  ;  metamorphosis  in- 
complete.   Ephemera. 

4.  Order  Odonata. — Abdomen  with  two  platelike  cerci ;  wings  mem- 

branous and  richly  veined,  not  folded  when  at  rest ;  month- 
parts  biting;  metamorphosis  incomplete,  sometimes  approaching 
completeness.     Libellula,  jEschna,  Agrion,  Diplax. 

5.  Order  Pteo/>^era.— Abdomen  usually  with  cerci;  wings  membra- 

nous, moderately  veined  with  few  cross-veins  ;  the  anterior  cov- 
ering the  posterior  when  at  rest ;  mouth-parts  biting ;  meta- 
morphosis incomplete.     Perla. 

6.  Order  Corrodentia.  —Abdomen  without  cerci ;    wings  sometimes 

wanting  (parasites  and  neuters),  membranous,  the  anterior  cov- 
ering the  posterior  when  at  rest ;  mouth-parts  biting ;  meta- 
morphosis incomplete  or  wanting.  Termes  (with  polymorphism), 
Atropos,  Liotheum,  Trichndectes. 

7.  Order  Thysanoptera. — Abdomen  without  cerci ;  wings  sometimes 

wanting,  narrow,  poorly  veined,  fringed  with  hairs  ;  the  anterior 
pair  covering  the  posterior  when  at  rest ;  mouth-parts  piercing 
and  sucking;  metamorphosis  incomplete.     Thrips,  Phl(Xothrips. 


linal  segments 


present.      Le- 


«. 


TYPE  TliACHEATA.  537 

Order  Rhpnchota.-Ahdom.n  without  cerci  ;    basal  portion    of 
anterior  wings  chitinous.  posterior  wings  and  tips  of  anterior 
membranous,  or  else  both  membranous,  the  anterior  the  larger 
or  both  wanting  ;  mouth-parts  piercing  and  sucking  ;  meta.nor- 
phosis  incomplete. 

Anterior  wings  chitinous  at  base  (Henuptera).  Anasa,  Notonecta, 
Belostoma,  Ranatra,  Hydrometra,  Halobates,  Cimex,  PediouUs 
(wings  wanting  in  the  last  two) 

"^"Jrr'n  "f  ;  ^"'''  "^^^^--^^^^^  iHomoptera).     Cicada,  Aspidi. 

in^letsf S:r  '^^'"''"'"■'  ^"'"'  ^^'"^^  "^'^  '^  ^^"""^ 
Order  6>.^.o^^.m. -Abdomen  without  cerci ;  anterior  wings  chi- 
tinous, covering  in  the  posterior  when  at   rest ;  mouth-parts 
biting  ;  metamorphosis  complete.  "''"  paus 

(a)  Tarsi  of  four  joints,  one  of  them  ver>  small  (Cryptote. 
tramera).     Coccinella. 

(b)  Tarsi  of  five  joints,  one  of  which  is  very  small  (Cn/ptopen- 
tainera).  Ourculionidae,  Clytm,  Saperda,  Monohammus, 
Boryphora.  ' 

(c)  Tarsi  of  posterior  legs  four-jointed,  of  two  anterior  pairs 
tive-jomted  {Heteromera).     Meloe,  Lytta. 

(^Tar.si  all  five-jointed  and    all  the  joints  of  equal  size 
{Pentamera).     Lampyris,  Elateridfe,  Melolontha,  Necro- 
phorus,    Staphylinidae,    Hydrophilus,    Qyrinus,    Bra- 
ofmms,  Harpalus,  Carahus,  Calosoma,  Ckindela. 
OvA^Neuroptera.-AMom^n  without  cerci ;  wings  membranous 
richly  veined  with  numerous  cross-veins  ;  mouth-parts  bidng  • 

11.  Order  Panorpato.-Abdomen  sometimes  with  cerci  ;  wings  mem- 
branous with  few  cross-veins;  mouth-parts  biting,  af  end  of 
cylindrical  rostrum  ;  metamorphosis  complete.  Panorpa. 
Order  r..c/.op<.,.a._Abdomen  without  cerci  ;  wings  covered  with 
hairs  or  scales,  posterior  ones  larger  and  folded  fanlike  wlieu 
at  rest ;  mouth-parts  sucking  ;  metamorphosis  comi)lete  Phnj. 
ganea,  Anaholia.  " 

Order  Lepidoptera.-Ahdomen  without  cerci  ;  wings  covered  with 
seaK  not  folded  when  at  rest,  though  they  may  overlap;  mol  h- 
parts  usually  sucking  ;  metamorphosis  complet^ 

Small  forms  (Microlepidoptera).     Tinea,  Carpocapsa,  Pyralid* 

Oigyia,  Telea,  Pierts,  Vanessa,  Papilio 

nous,  without  scales,  not  folded ;  mouth-parts  biting  and  lap- 
ping ;  metamorphosis  complete. 

Ovipositor  rfitrnnti!f>  with   n'^i"'iri  f-!<i-i^    /  A  .    T      i 

h..     T/      --■--"'■    ""^  poioon-giand  (Aculeata).    Apis,  Bom- 
bus,  Vespa,  Camponotus,  Formica. 


10 


13 


13, 


14 


628  INVERTEBRATE  MORPHOLOGY. 

Ovipositor  non-retractile,  without  poison-gland  (Terebrantia). 
Mmeumon,  Proctotrupes,  Fteromalus,  Microgaster,  Cynips, 
Selandria. 
15.  Order  Dipter a. — Abdomen  without  cerci ;  wings  sometimes  want- 
ing, only  the  anterior  pair  ever  present,  posterior  pair  repre- 
sented by  halteres  ;  mouth-parts  piercing  and  sucking ;  meta- 
morphosis complete. 

With  wings.     Culex,  Tabanus,  Musca. 

Without  wings.    Pulex,  Melophagus. 


LITERATURE. 

PROTRACHEATA. 

H.  N.  Hoseley.  On  the  Structure  and  Development  of  Peripaiua  capemis. 
Philosophical  Transactions  Royal  Society,  Loudon,  CLXiv,  1874. 

F.  M.  Balfour.  IVte  Anatomy  and  Development  of  Penpatus  capensis.  Quar- 
terly Journ.  Mlcroscop.  Science,  xxiir,  1883. 

E.  Oaifron.  Beitnige  zur  Anatomie  tmd  Histologie  des  Peripatus.  Zoologischc 
Beilriige,  i,  1885. 

J.  voii  Kennel.  Entwicklungsgeseldchte  von  Peripatus Edwardsii  und  P.  torqua- 
tus.     Arbeiten  des  3ool.  Instituls  Wnrzburg,  vii,  1885;  viii,  1886. 

A.  Sedgwick.  The  Development  of  the  Cape  Species  of  Peripatus.  Quarterly 
Journ.  Microscop.  Science,  xxv-xxviii,  18H5-1888. 

A.  Sedgwick.  A  Monograph  of  the  Species  and  Dintribuiion  of  the  Genua  Peri- 
patus.    Quarterly  Journal  of  Alicroscop.  Science,  xxvm,  1888. 


MYRIAPOUA. 

H.  C.  Wood.     The  Myriapoda  of  North  America.    Trans.  American  Philo8oj)Ii, 

Soc.,  XIII.  1865. 
C.  H.  BoUman.     'Ihe  Myriapoda  of  North  Ainerica.    Bulletin  U.  S.  Nutioiiiil 

Museum,  No.  46,  189.'}. 
R.  Latiel.     Die  Myriapoden  def  osterreiehischnngarisehen  Monarehie.    Wieii, 

lMHO-1884. 
J.  A.  Rydor.     The  Structure,  Affinities,  and  Species  of  Scolopendrella.     Tioc. 

Academy  Nat.  Sciences,  Pliiladelpliia,  1881. 
J.  Bode.     Ihly-reuas  lagurus,  ile  Geer.     Ein  Jieitrng  tur  Anatomie,  Morpholo;/ie 

und  Entwirklungsgeschichte  der  Uhilognathen.    Zeitschr.  fill-  d.  gesnnuiito 

Natiirwissensch.,  XMX,  1877. 
0  vom  Rath.     Beitnige  tur  Kenntniss  der  Chilognathen.     Boim,  1886. 
C.  Herbit.     Beilnig.   zuv  Kenntniss  der   Chilojwden.      Bibliotheca  Zoologica. 

II.  ft  IX,  1891. 
F.  0.  Heathoote.     T/is  Early  Development  of  lulus  terrestri^.    Qimrteriy  Journ. 

Microsc.  Science,  xxvi,  1886. 
r.  0.  Heathoote.     27ie  Postevihryonic  Development  of  lulus  terrettru.    Piiilo- 

....rxl.tnol    T-..^^       IJ, I    y,.,,  T l-_       ,.. ..,..„, 


TYPE  TRAOnEATA. 


52» 


IN8ECTA. 

CY8TEMATIC. 

A.  S.  Packard.    A  Guide  to  the  Study  of  Insects.    New  York   1889 
SirJohn^Lubbook.     A  Monograph  of  the  Collembola  and  Thysamra.    London, 

H.  Hagen     Synopsis  of  the  Neuroptera  of  Nmh  America.    Smithsonian  Inst 

Miscelliineous  Collection,  iv,  1861.  "»"umu  inst. 

C.  H.  Fernald.     Ihe  Orthoptera  of  New  England.     Boston   1888 
J.  I-  leconte.     Classification  of  the  Coleoptera  of  North  America.    Smithsonian 

Inst.  Miscellaneous  Collection,  iii.  1892 ;         1873  omuusonian 

J.  L.  Leoonte.     Nnmerous  Papers  on  Coleoptera  in  Proceedings  Acad    Nat 

Sciences,  Philadelphia.  ^  ^"^^• 

S.  K.Bcnii,r^    The  Butterflies  of  the  Eastern  United  States  and  Canada  with 

Special  Reference  to  New  England.     Cambridge   1889  ^«"«««'  ^^'^ 

J.  B.  Smith.     Contributions  toward,  a  Monograph  'of  the  Noctuida>  of  North 

America.    Proc.  and  Bulletin  U.  S.  Nat.  Museum 
A.  S.  Packard^    Monograph  of  the  Geomeirid  Moths.     Report  U.  S.  Geolodcal 

Survey  of  the  Territories.  X,  1876.  ^.  o   «eoiogicai 

E.  T.  Cre..on.    Synopsi..  of  the  Families  and  Genera  of  the  Hymenoptera  of 

A^nencanorih  of  Mexico  together  mth  a  Catalogue  of  DescnLl  SpZa^d 

hibhography.     Trans  American  Entomolo^rical  S(»ciety.  1887 
H  Loew  and  Baron  Osten  Sacken.     Monograph  of  the  Diptera  of  North  America 

bnulh,sonian  Institution.  Miscellaneous    Collection,  v,,   18C3  •  vi    1864 

viii,  1869;  XI,  1873.  «'"«  ,  vi.   1004  , 

8.  H.  Scudder.     The  Fossil  Insects  of  North  America.     New  York   1890 

J.  H^  aiul  A.  B.  Com.tock.    A  Manual  for  the  Study  of  Insects,    iihaca!  N.  Y. 

See  also  the  publications  of  the  U.  8.  Entomological  Commission  and  the 
o>  o.  V.  KUey,  A.  8.  Packard,  and  others, 

STKrcTl'HAL. 

H.  Orenaolier     Untersuch-mgen  iiher  das  Sehorgan  der  Arthropoden.     Omiin- 

E  Burge..      Contributions  to  the  Anatomy  of  the  MUkweid  liutterfl.,  (Danai, 
"'-^y.     Anniversary  Memoirs  B<..ton  Soc.  Nat.  History,  1880. 
18m  ^'^'"'^  ««'*  0/  tf>e  Garden  of  the  Gods,  etc.     Philndelphla, 

V.  Qrab«r.     We  chonhUmal  Sinnesorgane  und  das  GehOrder  Insekten.     Archiv 
[ti'"  niikroHk.  Anat.,  xx.  18H'.J.  ■'»-<»-utv 

^   "i^'^SSa.    ^"^  ^"""^^  '^''  ^^''^"-    Arbeiteu  a.  d.  zool.  Inst.  Wien, 


jJO 


Sir  John  Lubbock. 


INVERTEBRA TE  MORPHOLOO  T. 

The  Oi'igin  and  Metamorphosis  of  Insects.    London,  1883. 

Ants,  Bees,  and  Wasps.     London  and  New  York,  1883. 

J.  A.  Palmen.     Zur  vergleicJienden  Anatomie  der  Ausfurhrungsgiinge  der  Sex- 

ualorgane  beiden  Insekten.    Morpholog.  Jahrbuch,  ix,  1883. 
J.Carriere.    Die   Sehorgane    der    Thiere   vergleicJiendanatomisch    dargestelU. 

MUnchen,  1885. 
B.  Orassi.    Anatomia  comparata  dei  Tiaanuri  e  considerazioni  generali  tulV 

organizzazione  degli  Inaeiti.    Atti  della  R.  Accad.  Lincei,  Berie  lY.  it, 

1887. 
X.  Heider.    Die  embryonale  EiUwicklung  von  Hydrophiln    piceus  L.    Jena, 

1889. 
J.  Van  Rees.    Beitrdge  zur  Kenntniss  der  inneren  Metamorplioae  von  Mu&ca 

vomitoria.    Zoolog.  JabrbUcher,  iii,  1888. 
V.  Oraber.      Vergleicliende  Studien  am  Keimstreif  der  Insekten.     Denkaclir. 

Acad.  Wisseusch.  Wien,  lviii,  1890. 
H.  T.  Fernald.     The  Relationships  of  Arthropods.    Studies  from  the  Biolog, 

Labor.  Johns  Hopkins  Univ.,  iv,  1890. 
B.  T.  lowno.    Anatomy,  Physiology,  Morpliology,  and  Development  of  the  Blow- 
fly.   London,  1890-91. 
W.  M.  Wheeler.    A  Co7itribution  to  Insect  Embryology.    Journ.  of  Morphology, 

VIII,  1893. 
T.  H.  Huxley.    Anatomy  of  Cockroach.   Text-book  of  Anatomy  of  Invertebrate 

Animals.    New  York,  1878. 
W.  K.  Brooke.    Anatomy  of  Oratahopper.    Hand-book  of  Invertebrate  Zoology. 

Boston,  1890. 


'X. 


TYPE  ECHINODERMA. 


631 


sA    dargeatelU. 


CHAPTER  XVI. 


TYPE    ECHINODERMA. 

The  Echinoderms  are  exclusively  marine  organisms  and 

vary  considerably  in  shape,  some  forms  being  elongated  and 

vermiform,  others  stellate,  and  others  again  almost  spherical. 

Whatever  may  be  the  shape,  however,  a  well-marked  radial 

symmetry  can  be  distinguished,  which  suggested  to  the  older 

zoologists  the  association  of  the  members  of  this  group  with 

the  Ccelentera  in  a  type  Radiata.     The  radii  in  the  Echino- 

darma  are,  however,  almost  invariably  five,  instead  of  four  or 

six  or  some  multiple  of  these  numbers  as  in  the  Ccelentera  ; 

and,  furthermore,  while  in  the  Ccelentera  the  radial  symmetry 

represents  a  primitive  condition  and  any  departure  from  it 

towards  bilaterality,  as  in  the  Anthozoa,  is  secondary,  the 

reverse  is  the  case  witii  the  Echinoderma.     The  larval  forms 

of  this  group  are  strictly  bilateral,  and  even  in  the  adults 

certain  organs  or  parts  of  organs  interfere  with  the  regularity 

of  the  pentamerous  arrangement  and  bring  about  a  more  or 

less  pronounced  bilaterality. 

This  may  be  clearly  seen  if  one  of  the  stellate  forms,  such 
for  instance  as  the  ordinary  five-rayed  Starfish  (Fig.  240^, 
be  examined.  This  animal  consists  of  a  central  disk,  at  the 
centre  of  one  surface  of  which,  the  oral  surface,  the  mouth  is 
found,  while  the  anus  occupies  a  somewhat  excentric  position 
on  the  other  surface,  which  may  be  termed  the  aboral  or 
ai)ical  surface.  From  the  edge  of  the  disk  the  five  arms  or 
rays  project  outwards,  and  ahmg  the  median  line  of  the  oral 
surface  of  each  arm  there  extend  outwards  from  rings  around 
tlio  mouth  a  nerve-cord  and  a  hydroc(el  canal,  this  latter 
forming  a  part  of  a  peculiar  system  of  vessels  characteristic 

"• =•-.•  t.i,-.      ixi  ^.„^-^.j^jj^,jjj.g   .J.  j^^-.j_   ruaiation  of 

these  structures  out  along  the  arms,  and  the  arrangement  of 


532 


INVERTEBRATE  MORPHOLOGY. 


the  other  organs  for  the  most  part  in  conformity  with  the 
radiation,  the  arms  may  be  regarded  as  representing  the 
radial  axes  of  the  body,  the  interradial  axes  lying  in  the  in- 
tervals between  them.  If  now  the  aboral  surface  of  the  disk 
be  examined,  there  will  be  found  upon  it,  in  one  of  the  inter- 
radii,  a  peculiar  tubercle,  known  as  the  madreporiform  tuber- 


FiG.  'iiQ.—Asterias  arenicola  (after  Aoassiz  from  Vebrill). 


cle,  which  serves  to  place  the  hydrocoel  system  of  canals  in 
comnuinicati<  u  with  the  exterior  water.  There  is  but  ono 
such  tubercle,  and  but  one  canal  leading  down  from  it  to  tlio 
hydrocrel  ring  which  surrounds  the  mouth,  and  consequently 
there  can  be  but  one  plane  in  wliich  the  anini;il  can  be  di- 
vided into  two  siniihir  i)artH.  Therefore  the  Starfish,  thou;^di 
superficially  appearing  to  j)()ssess  a  radial  symmetry,  is  funda- 
mentally bilateral— a  statement  which  applies  etpially  well  to 
any  member  of  the  Echiuoderm  type. 

It  does  not  necessarily  follow,  however,  that  the  ])lHiie 
which  passes  through  the  madreporiform  tubercle  is  tin* 
luediau  plane  of  the  body.  The  larvo)  of  the  Echinodcniis 
are  strictly  bilateral  organisms,  no  sign  of  radiality  beinj,' 
found  in  thftm  in  an  early  stage  of  development,  and  it  would 
seem  more  satisfactory  to  take  as  tlie  median  j)lane  of  the 


TYPE  BCUINODBBMA.  533 

adult  animal  one  which  ccresponds  as  closely  as  possible 
-th  the  larval  median  plane.     The  madreporiform  tubercle 
...•rather  the  pore  which  corresponds  to  it    ancrthet, 
winch  leads  from  it  to  the  rudiment  of  the  iyd  oLl       '''t 
can  readily  be  made  out  in  the  larva,  of  most  forms  and 
can  be  seen  that  it  lies  to  the  left  of  the  median  p  aTe  "r  he 
l>«ly.      Indeed  in  the  larva,  of  some  Starfishes  two  no  e 
"ccur  at  an  early  stage  of  development,  one  to  the  left  and 
the  other  to  the  nght  of  the  median  plane,  the  latter  subse 
.  nently  disappearing.      The  madreporifor,;  tnbercle   mi .ht" 
therefore  be  regarded  as  lying  to  the  left  „f  the  median  ,Ze 

However  it  is  impossible  to  tell  how  much  modiHctio., 
has  taken  place  during  the  transition  from  the  bZ. ra    to 

l.e  radial  condition  and  it  is  not  impossible  that  the  g  eat  r 
portion  of  the  adult  represents  one  of  the  halves  tf  uL 
embryo,  the  other  half  remaining  more  or  less  „n  evelper 
Furtherniore  a  secondary  bilaterality  supervenes  in  ceiLt 
S  tl  f .^'"""f,"  .™''  H"l"".-"'oidea  which  does  no  a  ^  e 
with  that  indicated  in  the  precedinc  imra.rra,,!,  .,  ,  .  "'™ 
indeed  the  same  in  the  two  groups.     n'::r;;i .;;;:"; 

able  to  assume  a  perfectly  arbitrary  method  of  in,  Lit  uj 
he  radii  of  the  body,  calling  that  radius  whicl,  lie,  on        t 

e  madreporiform  tubercle  A,  that  which  lies  to  th  '  l',^ 

.s  when  the  animal  is  held  with  the  oral  surface     p war  K 

''wlir'  Z^'  f-  ''•/'.'"'"™'*''  "-"'-tion  of  the  h      1? 
..    atch.     The  interradii  may  be  in.licated  by  combininir  the 

■Iters  of  adjacent  radii,  the  interradiu,  beLeen  i     n.l    « 
l'"MJg  denoted  by  vl «.  "veeu  .1  ami    H 

The  bo,Iy-wall  in  the  Echinoderma  is  covered  on  the  out 
..le  by  a  usually  delicate,  and  in  .some  cases  cille     e" 
enn  which  ,„ay,  however,  be  indistinguishable  fr,  n       ^  , 
■■  nt   inesodennal   tissue,   in   certain    parts   of    t  le   b,    v" 
l-l.-w  this  ectoderm,  when  present,  comes  a  layer  oi  me   . 
maal   connective  tissue  consisting  of   relatively  few  Tel 
"iil  edded  m  a  more  or  less  Hbrillar  matrix,  and  in  tlds  co  , 
"ective  tissue  there  are  imb„d,l„,l  „„.„„,...,...  1.,  '"",  ".""- 

".  ^..me  forms,  such  as  the  Ho.oThuri'an;;  ^L^'XT  t^^^^ 


634 


INVERTEBRA  TE  MORPHOLOO  T. 


separated  from  one  another  so  that  the  body-wall  has  a  more 
or  less  leathery  consistency,  but  more  frequently  placed 
almost  or  quite  in  contact  with  each  other,  and  uniting  in 
most  of  the  Echinoids  or  Sea-urchins  to  form  a  firm  test  en- 
closing the  principal  vegetative  organs,  a  small  area  or  peri- 
stome around  the  mouth  alone  remaining  but  partially  calci- 
fied and  retaining  a  leathery  consistenc}'.  Spinous  elevations 
are  frequently  developed  upon  these  dermal  plates  (whence 
the  name  of  the  type)  and  may  assume  various  forms,  being 
in  some  cases  quite  loug,  movably  articulated  with  the  plates, 
and  supplied  with  muscles  so  that  they  may  aid  in  locomo- 
tion. 

The  arrangement  of  the  calcareous  plates  diflfers  greatly 

in  the  different  classes  which  com- 
pose the  type,  but  certain  of  them, 
distinguishable  by  their  position 
and  relative  arrangement,  reappear 
in  the  majority  of  the  classes. 
These  plates  are  situated  at  the  oral 
and  aboral  surfaces  of  the  body. 
The  oral  plates  are  not  so  constant 
nor  so  numerous  as  the  aboral  or 
apical,  and  show  a  tendency,  even  in 
those  groups  in  which  they  are  most 
highly  developed,  to  undergo  a 
greater  or  less  amount  of  resorption 
during  development,  being  frequent- 
ly more  pronounced  in  larval  than 
in  adult  life.  Typically  the  oral 
system  consists  of  a  central  oral 
plate,  the  orocentral,  unknown  in 
recent  forms,  but  occurring  in  cer- 
tain fossil  genera,  and  this  is  snr- 
rounded  by  a  riog  of  five  plates, 
which  may  bo  termed  the  oral  plates, 
and  which  nave  an  interradial  [)osi- 
tion.  Tin  ujiical  system  has  as  a 
central  pli*  ■  the  so-called  ceiifro- 
dorsfd  (Fig.  247,  CD),  which  in  some  i-tmg  is   re])laced  by  a 


Fig.  247.— Disk  and  Akm  of 

Zoroaxter,     s-iiowino     the 
Apical  System  of  Platks 

(after  Si.adkn). 
an  =  umis. 
cd  =  ceutio-ilorsal. 
7Tit  =  madieporite. 

T  =  tertliinal  plate. 

2  =  u.'ider-basals. 

8  =  basal':. 

4  =  radials. 


n^-Jf^^^^ 


TYPE  ECIIINODEIiMA. 


535 


unmber  of  small  plates  between  which  the  anal  openiug  of 
the  digestive  tract  is  to  be  found.     Formin-  a  ring  around 
this   are  frequently  live  plates  possessing  a  radial   position 
which  are  termed  the  nnder-basah  (Fig.  2^7,  2)  ancl  are  un- 
represented  in  certain  forms  ;  next  to  these  comes  a  secoud 
circle  of  five  plates,  the  bamls  (Fig.  247,  3),  which  are  inter- 
radial  and  correspond  to  the  oral  plates,  while  next  to  these 
again  is  a  third  cycle,  also  of  five  plates,  the  rndials  (Fig  247 
4),   whose   name    denotes    their   position.      Numerous ''other 
plates  may  intervene  in  the  various  groups  between  the  radials 
and  the  orals,  but  their  number  and  arrangement  is  not  suiH- 
ciently  constant  to  permit  of  homologies  ;  the  oral  and  apical 
systems  are,  however,  represented  more  or  less  perfectly  in 
all  but  one  of  the  classes,  and  consequently  deserve  special 
mention. 

A  well-developed  dermal  muscular  system  occurs  in  the 
Holothurians  in  which  the  calcareous  plates  are  scattered 
aa.l  the  body-wall  consequently  capable  of  considerable  con- 
traction and  expansion,  but  in  other  forms  it  is  very  much 
reduced.  In  those  forms  in  which  the  calcareous  plates  are 
simply  in  apposition  strands  of  muscular  tissue  pass  from 
plate  to  plate,  a  considerable  amount  of  movement  being  pos- 
sible, but  in  the  Sea-urchins,  for  example,  the  dermal  muscu- 
lature IS  almost  wanting,  being  reduced  to  bands  passing  to 
the  bases  of  the  movable  sp,ines  and  to  the  complicated  mas- 
ticatory apparatus. 

The  C(Klom  is  somewhat  complicated  in  its  relations,  which 
vary  considerably  in  the  ditierent  groui)s.  In  all  enterocctaic 
and  schizoc(Blic  portions  are  distinguishable,  the  former  in 
the  embryo  arising  as  pouchlike  diverticula  from  the  primi- 
tive intestine  or  enteron,  and  later  becoming  completely  con- 
stricted off  from  it.  Mucii  variation  occurs  in  the  later  his- 
tory of  the  pouches  in  the  various  groups,  but  in  general  it 
•nay  be  stated  that  one  of  them,  the  left,  has  a  portion  con- 
stricted  off  from  it,  which  forms  the  adult  water  va.<^cuhir  s-ys- 
>''i>i  or  hfilrocopi,  a  structure  characteristic  of  the  Echinoderms  • 
iiu.l  furthermore  this  same  left  enterocoel  communicates  with' 
'li(>  exterior  by  a  dorsal  jiore,  situated  in  the  interradius  CD 
ni.l  represented  in  the  adult  by  one  or  many  pores  opening 


536 


INVERTEBRA  TE  MORPIIOLOO  Y. 


upou  a  sievelike  calcareous  plate  known  as  the  mmhrporifonii 
tubercle  or  madreporite.  The  hydroccel  in  the  adult  commniii- 
cates  with  the  left  enterocoel  by  a  tube,  termed  the  stone- 
canal  from  the  deposition  of  calcareous  matter  which  occa- 
sionally takes  place  in  its  walls,  and  so  indirectly  opens  to 
the  exterior  through  the  madreporiforni  t\ibercle  (see  l\. 
265).  The  various  departures  from  this  arrangement  which 
occur  will  be  more  conveniently  considered  in  connection 
with  the  special  descriptions  of  the  various  groups ;  the  con- 
dition just  mentioned  may  be  provisionally  acce])tecl  as  rep- 
resenting the  typical  arrangement. 

After  the  separation  of  the  hydroccel  from  the  left  entero- 
coel, the  latter  and  the  enterocoel  of  the  right  side  increase  in 
size  and  finally  apply  themselves  closely  to  the  inner  surface 
of  the  bodj^-wall  and  to  the  outer  surface  of  the  digestive 
tract,  forming  the  peritoneal  lining  of  these  structures.  Wlieie 
the  two  ccelomic  sacs  meet  there  are  formed,  of  course,  two 
partitions  extending  from  the  body-Avall  to  the  intestine,  ami 
suspending  that  structure  between  them.  These  partitions 
are  the  mesenteries,  but  before  the  embryo  reaches  the 
adult  stage  one  of  these  mesenteries  disappears,  the  oilier 
persisting  in  a  more  or  less  perfect  form.  The  coiling  of  the 
intestine,  which  occurs  frequently  in  the  adult  forms,  brinjiis 
about  complications  of  the  course  of  the  >aesentery,  coui))!!- 
cations  further  increased  in  most  cases  by  the  formation  of 
other  partitions  which  may  traverse  a  greater  oi  less  portion 
of  the  coelom  either  longitudinally  or  transversely.  One  of 
the  transverse  partitio"  ■',  most  frequently  present,  separates 
off  more  or  less  completely  from  the  rest  of  the  coelom,  a  por- 
tion of  it  surrounding  the  pharyngeal  region  of  the  digestive 
tract  and  hence  termed  the  peripharyngeal  cavity,  while  iu 
gome  cases  a  perianal  cavity  may  similarly  bo  formed. 

The  hydrocoel,  whose  origin  has  been  described,  develojw 
into  a  tubular  ring  (Fig.  248,  cc)  surrounding  the  oesophagus 
quite  close  to  the  mouth.  Upon  this  ring  iu  the  interradii 
one  or  several  saclike  diverticula,  termed  Polian  vesicks  (/)), 
occur,  and  in  one  interradius  a  canal,  the  stoue-canal  (sr), 
passes  aborally  to  open  into  a  thin- walled  sac  terme<l  the 
ampulla  of  the  stone-canal,   which  is  iu  reality  a  portion  of 


TYPE  ECniNODERMA.  537 

tlie  left  enterocoel,  partly  or  wholly  separated  off  from  the 
rest   of  that   cavity.     This  ampulla,    as  already   mentioned 
communicates  with  the  exterior  through  the  madreporite.     In 
the  radii  tubes  {re)  arise  from  the  ring  which  extend  out  to 
the  aboral  extremity  of  the  body  in  the  elongated  and  spheri- 
cal  forms,  and  to  the  ends  of  the  rays  in  the  brachiate  forms 
terminating  frequently  in  tentacular  structures  (t)  which  pro^ 
trade  to  the   exterior,  i)ushing    the    ectoderm    before  them 
Along  the  course  of  these  tubes  lateral  branches  are  given  off 


Fig.  248.-DIAGRAM  to  show  the  Arrangement  op  the  Hydrocosl  of 

AN    ECHINODERM. 

a  =  ampulla.  p  ^  PoU^j.^  ^^^^^^.^^ 

as  =  axial  sinus.  re  =.  raiiial  caual. 

cc  =  circular  canal.  sc  =  stoue-canal 

M  =  madreporite.  t  =  terminal  leutacle. 

tf  =  tube-foot. 

which  terminate  either  in  tentacular  structures,  or  else  in 
tubes  terminating  in  a  sucker,  which,  since  they  play  an  im- 
portant role  in  locomotion,  are  termed  hihe-feef  (tf).     In  nmny 

orras  a  globular  reservoir  or  ampidla  (a)  is  attached  to  each 
tube-toot,  and  valves  are  found  at  the  junction  of  the  branch 
passing  to  the  foot  with  the  radial   canal,  so  that  the  foot  can 

)e  extended  to  a  considerable  distance  by  the  contraction  of 
tlie  muscles  in  the  walls  of  the  ampulla  and  the  consequent 

oionig  of  water  into  it.  By  means  of  the  sucker  they  may 
tlieu  adhere  to  foreign  objects,  and  their  contraction  then 
pnHluees  a  movement  of  the  bodv  towards  the  point  of  fixa- 
tion. 


1i*fiS4 


638 


INVERTEBRATE  MORPHOLOGY. 


\>h 


In  connection  with  the  stone-canal  a  peculiar  body  is 
developed  r\  most  forms.  It?  function  is  a  matter  of  ques- 
tion, it  hnviug  been  at  one  time  taken  for  the  heart  and  at 
another  for  a  gland.  It  is  generally  termed  the  ovoid  gland 
(Fig.  265,  og)  and  consists  of  a  mass  oi  cells,  derived  from  the 
peritoneal  lining  of  the  enterocoel,  grouped  together  to  form 
a  more  or  less  solid  mass.  The  oral  end  ci  the  gh^nd  is  pro- 
longed into  a  cordlils  biructure  which  seems  to  enter  into 
close  relationships  with  the  oral  lacunar  ring  (see  below),  while 
at  the  other  it  is  continued  out  to  enter  into  close  relationships 
with  the  reproductive  organs  in  a  manner  that  will  be  de- 
scribed when  treating  of  those  organs.  Surrounding  the 
gland  is  a  sinus — the  axial  sinus  (Fig.  265,  as) — sejjarated  off 
from  the  enteroccel  and,  in  some  forms,  in  communication 
with  the  ampulla  of  the  stone-canal,  and  the  portion  of  the 
gland  which  passes  off  towards  the  reproductive  gland  is  also 
surrounded  by  a  sinus,  or  rather  lies  in  the  wall  of  a  sinus 
which  may  or  may  not  communicate  with  the  axial  sinus  but 
has,  like  it,  origin  from  the  general  enterocoel. 

"What  has  been  termed  a  blood  system  is  usually  present, 
consisting  of  a  tubular  ring  surrounding  the  cesophagus,  and 
lying  between  the  hydrocoel-ring  and  the  nerve-ring.  Five 
branches  may  extend  oft'  from  it  along  the  radii,  preserving 
the  same  relatio]is  to  adjacent  structures  as  does  the  ring. 
These  spaces  seem  to  be  schizocoelic  in  their  character,  and 
may  be  termed  the  schizocoelir  ring  and  radial  schizocoelic  sinuses 
in  order  to  avoid  confusion  with  another  system  of  vessels 
which  sometimes  lie  within  the  sinuses  and  have  also  been 
termed  blood-vessels.  This  latter  system  may  be  termed  the 
lacunar  system,  and  is  composed  of  a  network  of  vessels  lying 
in  the  walls  of  the  intestine,  and  collecting  usually  into  a 
perioesophageal  ring  or  plexus  (Fig.  265,  Ir),  with  which  also 
the  ovoid  gland  comes  into  connection.  In  the  Echinoids, 
as  has  just  been  indicated,  prolongations  of  this  perioesophageal 
ring  or  ])lexus  extend  out  in  the  radial  schizocoelic  sinuses. 

The  fluids  contained  in  the  sinuses,  lacuuio,  hydrocrel,  and 
enterocoel  are  all  very  similar,  consisting  of  a  plasma  contain- 
ing amoeboid  cells  sometimes  deeply  pigmented.  In  a  few 
forms  hsemoglobin  is  present ;  in  the  Ophiuran  Ophiactis  it  is 


II 


TYPE  ECIIINODEBMA.  539 

contamed  iu  flat  nou-uucleatecl  disks,  resemWiug  Mammaliau 
red  blood-corpuscles,  floatiug  iu  the  plasma  "f  11""™*"" 
™seula.-  system ;  m  the  Holothuriaus,  Thyo,^  aud  CucJ^T, 
>l  .s  howevev  coutaiued  iu  au^boid  corpuscles,  ^hicTa  e 
..ost  ab„u,laut  m  the  ccelomic  fluid,  though  occur  iug  dso  L 
tlie  water  vascular  tubes.  ^ 

The  digestive  tract  is  generally  more  or  less  twiste,!  iuto  a 

:i!ht  T  IT'  "'  '"  r'"^  Holothuriaus,  it  appea     to 
b   .straight,  ,t  m  to  be  regarded  as  a  much-drawu-oit  spiral 
.nee   he  mesentery  still  retains  a  spiral  arrangement.     I         ' 
Ho  othunaus,  Eclnuoids,  and  Starfishes  it  opens  on  the  abo  d 
™  ace  of  the  body,  but  in  the  Crinoids  it  is  bent  upcn  itse 

hat   he  anus  ,s  on  the  oral  surface.     In  some  Itarfls  .e 

tr  ,ctu,'.e    ^"'"rr  "°  ™"'  '•"  l^'-''^»'-     ^'""O"''  accessory 
t.uctu,es    masticatory  apparatus,  ccecal  pouches,  etc     are 

Sjuitnirtr ''""'""'' "-'"  "-*'-  -/^« 

The  nervous  system  may  be  regarded  as  being  composed  of 

meut  as  the  water  vascular  tubes,  consisting  of  a  circumoral 
or  a  pencesophageal  ring  from  which  fivA  ,.^,i;,l      "™"'°"" 
offiFiiT  9fi^  «,.       1      .   """'"""""'  nveiiidial  nerves  pass 
>«  (lig.  26o.  vr  and  ,■»).     In  the  Starfishes  and  Crinoids  the 
»tne  system  is  imbedded  in  the  ectoderm,  but  in  other  for    ' 
.inks  within  the  body-cavity.     From  it  branches  pa  s    n 
ulsat  the  mouth  to  supply  the  walls  of  the  oesophagus  ami 
ft.     branches  form  a  network  covering  the  surface  "     te 
W>,  supplying  the  sense-organs  which  m.ay  occur  thereo  , 
Uu.  radial  nerves,  in  addition  to  sending  branches  to  joi.  tl  e 
p  derma    plexus,  supply  the  ambulacral  system.     Th  »  po 

of  th,    nervous  system  may  be  termed  the  epideral 
1".  .on,  and  the  second,  inasmuch  as  it  supplies  the  m  i,, ritv 

:.;:  "'ti-':;"'  f --3-.  ■"■^3-  be  ter^iirthe^r::;; 

wiuoi  is,  but  when  present  accompanies  in  gener.al  the  eni 

:^'s:r;:tf::t'''^fz.rr:t--:^;;"'^' 

-  '.<•  entirely  wanting  in  the  Holothurians,  b!it  w,:eV:!r:: 


'>  if- 


640 


TN VERTEBRA  TE  MOliPUOLOG  Y. 


cousists  of  a  xm^  situated  at  the  aboral  surface  of  the  boilj', 
sending  off  branches  to  tlie  reproductive  organs  as  well  as,  in 
some  cases  at  least,  forming  anastomoses  with  the  epidermal 
83'stem. 

Sense-organs  of  various  kinds  are  developed.  Tactile 
tentacles  occur  at  the  extremities  of  the  radii  of  some  forms 
and  round  the  mouth  in  others,  while  in  the  softer-skinncnl 
Holothurians  tactile  papilhe  may  occur.  Eyes  occur  at  the 
extremities  of  the  radial  nerves  of  the  Starfishes,  and  have 
also  been  described  as  occurring  in  some  Echinoids,  while 
otocysts  occur  in  some  Holothurians,  sometimes  in  considera- 
ble niimbers. 

No  special  excretory  organs  occur  in  the  Echinodermuta, 
the  am(i'boid  cells  of  the  cadomic  fluids  perhaps  serving  iu 
some  cases  to  remove  the  Avaste  substances.  They  have  beeu 
observed  to  pass  through  the  bodj'-wall,  in  regions  where  it  is 
thin,  to  the  exterior  and  there  degenerate.  For  the  nujst 
part,  however,  the  waste  products  are  deposited  in  the  tissues, 
or  else  pass  to  the  exterior  by  osmosis.  In  the  Holothuriaus 
special  branched  appendages  of  the  terminal  jjortion  of  the 
intestine  apj^ear  to  take  some  part  in  excretion,  but  suck 
organs  do  not  occur  in  other  groups. 

The  Echinoderms  are  almost  invariably  bisexual,  and  the 
reproductive  organs  are  usually  situated  in  the  interradii. 
They  are  enclosed  in  a  special  coelomic  sinus,  the  genital  .sinus, 
in  whose  wall  may  be  found  the  branches  of  the  aboral  nerves. 
From  each  organ  or  mass  of  reproductive  cells  a  cellular  ccud, 
the  genital  racMs,  surrounded  by  the  sinus  may  be  traced, 
except  in  the  Holothurians,  to  the  ovoid  gland,  and  it  a))pears 
probable  that  iu  some  cases  at  least  the  reproductive  cells 
originate  in  a  part  of  the  ovoid  gland  and  migrate  to  the 
reproductive  organ  along  the  rachis,  becoming  mature  in  tlieir 
final  position.  The  openings  by  Avhich  the  reproductive  ele- 
ments pass  to  the  exterior  vary  both  in  number  and  position 
in  the  different  groups,  but  are  usually  situated  on  the  aboral 
surface  of  the  body. 


TYPE  ECIIINODEltMA. 


fi41 


I.  Class  Crinoidea. 

The  Crinouls,  or  Sea-lilies  (Fi<,^  249),  coustitute  a  group  of 
forms  whicli  lii  the  earlier  geological  i)erioas  reached  a  hi-h 
orade  of  developmeut,  but  to-day  the  class  is  represented  by 
eumparatively  few  forms,  for  the  most  part  couHued  to  deep 


Fig.  24!d.—Pentiicvinus  madenranus  (after  Wyville  Thompson  from  Hertwig) 


water.  One  of  the  most  characteristic  features  of  the  group 
IS  the  presence  of  n  more  or  less  elongated  cylindrical  stalk 
one  end  of  which  is  attached  to  stones  or  other  objects  which 
snrve  as  supports  for  the  animal,  while  at  the  other  end  is 
the  body  proper,  which  has  a  more  or  less  cuplike  form.  In 
the  peculiar  genus  Ilolopus  the  stalk  is  thick  and  short,  and 
may  be  described  rather  as  the  prolonged  apex  of  the  body 


642 


mVEUTEDUATE  MORPHOLOGY. 


U 


4 


than  as  a  ilistiuct  stalk,  while  in  other  forms,  such  as  Antedon 
and  Actinometm,  the  stalk,  though  present  in  young  forms,  is 
entirely  wanting  in  adult  life,  during  which  the  animal  is  free- 
swimming,  though  having  the  power  of  anchoring  its.'lf 
temporarily  to  solid  objects  by  means  of  a  number  of  slender 
processes  termed  cirri  which  project  from  the  apex  of  the  cud 
(Fig.  251,  c).  ^ 

The  lower  portion  of  the  cup,  or  calyx,  is  formed  by  a  num. 
ber  of  series  of  calcareous  plates  united  to  each  other  l)v 
sutures,  while  its  mouth  is  covered  in  by  a  flat  or  dome- 
sliaped  disk  in  which  calcareous  plates  may  or  may  not  lie 
present.     In  the  centre  of  the  disk  is  the  mouth  of  tlie  animal, 
while   to  one  side  is  tlie  anus,  lying  in  the  int^rradius  ClK 
From  the  mouth  Ave  grooves,  known  as  the  anibulucral  (jrooves, 
extend  outwards  towards  the  margin  of  the  cup,  and,  near  the 
margin,  brjinch,  being  tiien  continued  outwards  on  the  f)ial 
surfaces  of  ten  arms  which  arise  from  the  junction  of  the  disk 
and  calyx,  frequently  branching  in  tlioir  course,  and  bearii]<r 
along  their  sides  a  series  of  siiort  processes  resembling  them 
in  structure,  and  termed  tlie  phmnlcs,  upon  which  the  amhu- 
lacral  grooves  are  also  continued.    Tliose  arms  are  capal)]e  of 
considerable  movement,  being  at  one  time    extended  out  at 
right  angles  to  the   body  or  even  reflexed,   and  at  anotliH- 
coiled  up  circinnately  over  the  disk,  the  pinnules  being  at  tlir 
same  time  bent  inwards  towards  the  median  axis  of  the  arm. 
The  stem  when  ])resent  consists  of  a  number  of  disklik.-  oi 
cylindrical  calcareous  plates,  placed  one  on  top  of  the  other, 
being  held  together  by   bands  of    connective  tissue,  and  is 
traversed  by  a  central  canal  containing  prolongations  of  certain 
of  the  visceral  structures.     1'lie  terminal   plate  serves  as  (lu- 
point   of   fixation,    the    plates   immediately  above  it   havini; 
attached  to  them  a  number  of  cirri  which  assist  in  fixation 
and  are,  like  the  stem,  c()m})osed  of  calcareous  plates  contain- 
ing i)rolongations  of  the  central  canal.     In  some  forms,  such 
as  Pentacrinufi,  whorls  of  cirri  also  occur  at  intervals  all'al..ni,' 
the  stem,  those  plates  from  which  they  urise  l)eing  teiimd 
nodal  plates,  a  varying  number  of  plates  destitute  of  ciiri 
occurring  between  two  nodes  in  diflerent  genera.     In  cerfnii! 
genera,   however,  such  as  IhjnrnnuN  and  lihizocrinus,  tli.se 


TYPE  ECHINODERMA.  543 

«tem  cirri  are  entirely  wanting  except  near  the  point  of  fixa- 

The  uppermost  plate  of  the  stem  is  usually  regarded  as 
fonniug  the  apex  of  the  calyx  and  is   termed  the  ceTrlTLd 
Above  this  comes  in  most  recent  forms  a  series  of  usuaHy  fi  e 
sometimes  three)  interradial  plates,  the  basals  (FigS    f  bu 
one  genus    naun^nfocrinus,  there  occurs  between  th  ecen 
tiodorsal  and  basal  plates  a  series 
of    five    radial    plates    which    are 
termed  the  parabasals    or    under- 
l)Hsals,  and  which  have  also  been 
found  to  occur   in  the  embryo   of 
Antexlon,  later  on  fusiug  with  the 
centrodorsal.     Succeeding  the  ba- 
sals are  from  two  to  seven  circles 
<^f   radials   (r),    each    circle    being 
also  composed  of  five  plates  termed  -  ^j^^ 

tlio  first,  second,  third,  etc.,  radials    Fm.  ,'350.-T„k.  apica.  system 
according     to      their     succession       "^  Melocrinm  (fossil)  (fro,,, 
counting    from    the    centrodorsal.       "' 
In  Aniedon  and  some  of  its  allies 
tiie   number   of   cycles   of   radials 
s<^en    from    the     exterior    is     one 
.sli<»rfc  of  the  actual   number  which 

^xists,    the   first   radials    being   overlapped    and    covered    in 
>v     he   second:    and    furthermore   in    the    same   forms   the 
b  sals  have  also   been  pushed,  as  it  were,  within   the  calvx 
lave  fused  to  iorm  a  single   plate,  the  so-called  .o.sW/. 
MI  g.  251,  7?o,v).  winch  rests  upon  the  centrod<.rsal.  par- 
uly  dosing  a  cavity  in  that  plate.     The  terminal  ra.lials 
sually  present   two  articuL-tting  facets  in    their   distal  sur- 
t.U'es  and  are  generally  know.,  as  the  r,.r;7AnvV.v  (Fi.  2r,0  a) 
-cc    he  arms  articulate  with  them.     In  the  ^.n^TljJ: 
...  betw^^n  each  pair  of  first  radials  an  interradial  plate 
-n  s.  a  condition  frecpiently  found  in   fossil  genera  ii),  but 
sua^y  wanting  in  recent  forms.     These  various  plates  which 
<;;•.  t.tute  the  apical  system  are  united  by  sutures,  the  edce« 
^.  .lie  various  senes  of  plates  coming  into  contact,  s..  that  a 
*H'"Hupportisationlod  for  the  arms 


BnoNN), 

a  -  Hxillary  plates. 
*  ~  ))!isa!  plates. 
i  =  iiilenadial  plates. 
r  =  radial  plates. 


544 


INVERTEBRATE  MORPHOLOGY. 


These  are  iu  reality  continuations  of  the  radial  series  of 
plates  ;  iu  fact,  iu  some  forms  certain  of  the  radials  appear  to 
enter  into  the  formation  of  the  arm.  Iu  most  forms,  however, 
a  series  of  arm-plates  arises  from  each  facet  of  the  live  axillar}- 
plates,  so  that  the  arms  are  ten  iu  number — a  condition  which 
finds  an  exception  in  the  remarkable  genus  Thaiimatocrinns^ 
which  possesses  but  five.  In  some  forms  these  ten  arms 
branch  dichotomously  ;  the  plates  intervening  between  tlio 
axillaries  and  the  first  branchiug  are  termed  brachials,  those 
between  the  first  and  second  branchings  distichals,  and  those 
between  the  second  aud  third  branchings  palmars — terms 
which  are  useful  in  systematic  de  ^criptious.  These  various 
plates  are  united  together  b}'  ligaments  and  muscles,  or  else 
by  ligaments  alone  (this  last  form  of  union  being  known  as  a 
syzj/(jy),  the  movements  of  the  arms  noted  above  being  thus 
rendered  possible.  The  pinnules  repeat  the  arm  iu  tlieir 
structure,  though  usually  on  a  much-reduced  scale.  They 
are  situ  ited  on  the  joints  separatiug  consecutive  plates  of  tlie 
arms,  aud  are  j)laced  alternately  on  the  right  and  left  sides 
of  the  arm  which  bears  then).  They  appear  at  first  to  have 
been  produced  by  lateral  budding  from  the  joints,  but  closer 
examination  indicates  that  in  reality  they  represent  a  braiidi- 
iug,  one  of  the  brauches  remaining  small,  while  the  other  in- 
creases in  size  and  ])laces  itself  in  the  direction  of  the  axis  of 
the  arm.  The  whole  arrange nnuit  is  comparable  to  that  form 
of  inriorescence  termed  by  botanists  a  scorpioid  cynu^  tlie 
pinnules  re]>resenting  the  riower-])edicels.  Owing  to  the 
])inuules  being  iu  reality  one  of  the  branches  of  a  dich(;tt)my, 
it  is  evident  why,  in  those  forms  iu  which  the  arms  braucli, 
there  is  uo  pinnule  at  the  joiut  where  the  brauching  ot-curs; 
iu  addition,  however,  pinnules  are  also  lacking  on  sy/ygi.il 
joints,  so  that  their  r^igular  succession  )uay  be  somewhat  dis- 
turbed. 

As  regards  the  (U-al  systmn  of  plates  an  nro-ccnfral  is  found 
in  souu'  fossil  forms,  but  is  unrepresented  in  recent  gouerii. 
A  circle  of  five  interradial  oral  plates  is  found  iu  Jlolnpns, 
/thiz<K')'iuu,s,  //j/ocrinm,  lltanmaimrivm,  aud  ('ahnmn'rlims, 
ami  iu  the  stnlked  larva  of  Antcdon,  but  iu  the  adults  of  this 
latter  form  and  iu  other  genera  thau  those  mentioned  these 


TYPE  ECUINODEHMA. 


645 


plates  disappear  duriug  growth,  the  disk  beiug  either  u.aked 
or  covered  by  a  number  of  small  plates  which  are  termed  un^ 
amUdacrals,  certain  of  whicli  lying  on  either  side  of  the  ambu- 
lacral  grooves  receive  the  special  name  of  adamhulacrah  or 
covering-plates.  ' 

The  ectoderm   cannot  usually  be  distinguished  over  the 
surface  ot  the  calyx  or  on  the  stem,  but  is  present  on  the 
chsk  and  on  the  oral  surfaces  of  the  ain.s  and  pinnules,  being 
there  non-ciliated  except  along  the  ambulacral  grooves      It 
rests  upon  a  connective  tissue  in  which  the  calcareous  ,>iates 
are  developed,  and  from  which  strands,  frequentlv  with  cal 
careous  spicules  imbedded  in  them,  usually  travers;  the  body-" 
cavity-     Ihe  ligaments  which  unite  the  plates   of   the  arms 
and  stern  are  formed  of  this  connective  tissue,  and  contractile 
hbres  of  a   peculiar  character  are  sparingly  developed   in  it 
stretching  across  the  non-syzygial  joints  of  the  arms,  pinnules' 
and  cirri,  and  probably  also  reaching  a  slight  developmen; 
111  the  stem.  ^ 

The  internal  structure  of  the  Crinoids    is  known  i^rinci- 
pally  from  observations  on  Antedon,  and  the  following  account 
represents  what  occurs  in  that  form.     The  ccelom,  as  alreadv 
stated,  is  t.-aversed  by  numerous  strands  of  connective  tissue 
ami  primarily  consists  of   two  cavities  separated  from  each 
other  by  a  mesentery,  each  cavity  being  continued  out  into 
he  arms,  forming  the  oral  and  alu.ral  canals  of  these  struc 
ures,  at  the  extremities  of  which  they  unite.     The  mesentery 
does  not    however,  long  persist  in  its  entiretv,  but  the  two 
cavities  fuse,  new  n.embranes,  h.nvever,  arising  and  ,livi,lin- 
then,   m  some  species  of  Antod,n,.     One  of  these  mend.ranes 
(Ug.2;>l,  y.s.)  Mil-rounds  the  intestine  and  forms  the  visceral 
sac    Its  presence    rendcM'ing   the  evisceration  of  Aiitrdon  an 
I'asiy.accomplished  proc-ess  and  one  which  is  n.ade  use  of 
•y  the  annual  in  unfavorable  conditions,  a  new  visceral  mass 
-.ng  later  regenerated.     The  portion  of  the  ccelom  which 
li.'H    peripherally  to    this  sac  is    termed   the   circumvisceral 
l""-tion  (r.),  and  that  within  it  the  intervisceral  He),  the  latter 
containing  an   axial  cavity  (J..)  enclosed  by  a  membrane  sim. 


p.  VI HC- 


rul  Hut=  and  continuous  with  the  oral  co>i 


I 


cavities  {oc)  of  the  arms,  tiie  aboral 


omic 


cavities  ((/(•)  coiumuuicat- 


046 


INVERTEBRATE  MORPHOLOGY. 


iug  with  the  circumvisceral  coelora.  A  portiou  of  one  of  the 
coelomic  cavities  at  au  earl_y  stage  becomes  cut  off  from  the 
rest  of  the  coelom  aud  divided  iuto  five  chambers  whose  walls 
are  formed  of  a  deuse  fibrous  membraue.     This  constitutes 


•\s 


Fig.  251.— Veuticai.  Section  rnRoroii  Antedon  (combination  of  flgures  liy 

l,ri)w:i;  ami  MAi'snALi.t. 


cc  —  ahoml  caiml  nl'  ann. 
an  —  aboral  iutvc. 
Aj!  —  nxial  sinus. 
Br  =  hr.Mi'hiiil  jjliitcs. 

C  =  cirri. 

cc  =  circuiiiviscoml  ciivity. 
CD  =  ccntiodorsal  plute. 

CO  —  central  oryaii. 
Do  —  ilori-al  tirgmi. 

gr  —  geiiiliil  nichls. 

/=  intcHliuc. 

id  =:  intcrvlsceral  cavity. 


M  —  uioulii. 

oc  =  oral  cavity  of  arm. 

on  =  oral  nervf-riuj.^. 

R  —  radial  piatts. 

rh  —  radial  lacunar  vessel. 
rn  —  radial  epithelial  nerve. 
VOB  —  rosette  plate. 
r?o  =  radial  hydrocojl-caual. 

«c  =  stone-caual. 

T  —  oral  tentacle. 

vs  —  visceral  septum, 
wp  —  vvaler-pore. 


the  chambered  organ  (ro).  whicli  in  Antalun.  lies  in  a  cnviiy 
in  tlie  centrodorsal  pltite  and  is  roofed  over  by  the  rosette- 
phite,  l)ut  in  other  forms  simply  rests  upon  the  centrodorsal; 
communioating  with  it  is  the  lower  end  of  a  somewhat  citih- 
suaped  structun*  termed  the  ihprmil  'Wfjun  [Do),  wliicli  \no- 
jects  orally  i)arallel  to  the  axial  co'lomic  ctivity. 

The  e|>itlieliuni  of  the  aborid  codouiic  cavities  of  the  atiiis 
is  ditferentijited  hero  tind  there  into  peculiar  organs  the  ciii- 


TYPE  ECIIINODERMA. 


547 


1  of  flKiires  by 


uted  cups,  consistiu^^  of  slight  tlepressic.ns  lined  by  columnar 
cells  eacli  of   wiii.h    bears  a  long  ciUunu     These    cups  are 
especially  abundant  in  the  pinnules,  and  serve   to  create  a 
circulation   of  the   crelomic  Huid,  which,  as  in  other  Echino- 
(lerms,  contains  numerous  amueboid  cells  lioatiug  freely  in  it 
The  water  vascular  system,  or  hydroccjel,  consists  of  a  riuL^ 
surrounding   the   mouth,   and   sendi.ig  outwards   five   radial 
canals  {rw)  which  lie  below  the  ambulacral  grooves  and  are 
continued  along  the  arms  and  pinnules.     Occasionallv  sub- 
ambulacral  calcareous  plates  are  developed  in  the  connective 
tissue  bel(,w  the  radial  canals,  and  in  some  fossil  forms  these 
plates  assume  a  regular  arrangement  in  two  rows.     At  regu 
lai-  lutervals  along  the  arms  are  situated  the  ambulacral  ten- 
tacles,  which  are  fingerlike  outpouchings  of  the  radial  canals 
.  estitu  e  of  terminal   >  -ckers  and  are  arranged  in  groups  of 
three,  the  canals  being  somewhat  enlarged  in  .he  region  where 
they  occur,  an  indication  perhaps  of  the  ampulho  found  in 
other  groups;   in  some  forms   the   cavities  of  the   tentacles 
seem  t<.  be  united  with  those  of  the  canals  only  by  exceed 
iiigly  small  orifices,  which  may  be  closed,  since  the  tentacles 
111  their  greatest  contraction  always  remain  filled  with  fluid 
111  the  neighborhood  of  the  mouth  ar,>  a  number  of  oral  ten- 
tacles (Fig.  251,  7')  arising  directly  fron,   the   oral  rin.^   and 
.lilleriug  from  the  anibulacral  tentacles  in  not  being  armn.>ed 
in  grcnips  of  three.     From   the   oral  ring  there  also  arise"  in 
Anteaon  a  uumber  of  ciliated  tubes  (.r)  which  open  into  the 
cjelomic  cavity,  each  one  corresponding  to  a  stone-canal  of 
t  h;  othei   Echinoderms.     In  AntaJon  there   are   as  many  as 
thirty  of  these  canals  in  each  interradius.  and  in  Prntavrinm 
an  even  greater  number  occurs  ;  but  in  other  forms  they  may 
he  fewer,  Mizucrinus,  for  exrunple,  possessing  onlv  ftve  in  all 
one  being  sitna' h1  in  each  interradius.     In  the  larva  of  Jnfri 
'l<»>  there  is  .,.t  tvi  early  stage  only  one,  communicating  with  a 
I'-rtion  of  on-    >!  the  primary  cielomic  cavities,  which  on  its 
jMit  o])en8  to  the  exterior  by  a  pore,  an  arrangement  Nvhich 
may   be    regarded  as   typical   for   the  Echinoderms.     Later 
iowever,  this  portion  of  the  c.^lo.aic  cavitv  degenerates,  and 
the  canal   ihi  ,i   opens   directly  \nU.  tiie  ireueval  cu-lom,  and 


t[ 


ns 


communicates  with  the  exterior  by  th 


y  the  pore.     In  subse- 


648 


INVERTEBltA TE  MORPIIOLOG Y. 


n 


queut  stages  additioual  stoue-cauals  develop  from  the  oml 
riug,  and  at  the  same  time  additioual  pores  develop  iu  the 
walls  of  the  body,  forming  what  are  called  the  calyx-pores 
(icp).  These  may  reach  a  considerable  number,  it  being  esti- 
mated that  iu  Antedon  there  are  uo  less  thau  fifteeu  hundred 
of  them  scattered  over  the  disk;  iu  rjiizocrinus,  llyocrinnH, 
and  Holopus,  iiowever,  there  are  only  five  pores,  one  pierciiig 
each  of  the  oral  plates  present  in  these  forms. 

The  schizoccelic  system  consists  of  live  radial  sinuses  (Fi- 
251,  rh)  lying  between  the  radial  hydroco^l   vessels  and  tl?e 
more  superficial  radial  nerve,  together  with,  according  to  some 
authors,  a  circular  sinus  surrounding  the  mouth  iuto  whicli 
til"  radial  sinuses  open.     A  plexus  of  lacuna  occurs  in  the 
Avails   of  the  intestine,   and  another  surrounds    the  a'soplui- 
gus,  ,;his  latter  in  part  aggregating  itself  into  a  structure  re- 
sembling r,  lymphatic  gland  and  known  as  the  spongy  body; 
the  dorsal  organ  likewise  contains  a  dense  network  of  tnl)e,s 
lined    with  epithelium.     Ahmg  the  sides   of   the  hydrocol- 
canals,  in  the  disk,  arms,  and  pinnules,  alternating  in  the  two 
last  with  the  triads  of  tentacles,  in  the  walls  of  the  intestine, 
and  occasionally  elsewhere,  there  are  imbedded  in  the  con- 
nective tissue  yellowish  spheiical  bodies  known  as  the  hocvh};. 
The  interior  of  ench  sacculus  is  lined  with  cells,  and  contains 
a  number  of  pyriform  masses  formed  of  small  highly-refrac- 
tive spherules,  apparently  of  an  albuminoid  substance.     Tlie 
function  of  tliese  bodies  is  very  obscure  ;  they  have  been  le- 
garded  as  organs  for  secreting  carbonate  of  lime,  as  excretory 
organs,  as  parasites,  as  mucous  glands,  and  lately  as  organs 
of  reserve  iu   which   proteid    matter  may  be  stored  up  for 
future  use.     At  present,  however,   the  question  is  an  ojn^ii 
one,  and  a  function  cannot  with  certainty  be  assigned  to  tlicni. 
The  mouth  (Fig.  251,  m)  is  usually  situated  at  the  centre 
of  the  oral  disk,  and   opens  into  a  simple  tubular  intestine 
which  coils  once  round  the  cadomic  cavity  in  the  direction  of 
the  hands  of  a   watch   and  then,  ])endiug  upon  itself,  turns 
orally  to  open  in  the  interradius  CD  upon  tlie  disk.     In  .\<- 
iinometra,  a  genus   closely  related   to  Antedon,   the  intestine 
lies  iu  four  coils,  but  there  is  as  a  rule  little  variation  from  tlic 


TYPE  ECIIINODEUMA. 


649 

i"  the  lower"  i^Tr''"   """"«'^«"*  *J-»-  -^tire  course 
i^jeis  ol  the  ectoderm.     The  aboral  system  is 


Fm.  253.-DiAonAM  of  the  Arkang^micnt  op  the  Abor.i    at 

«  =  arms. 
B;- =  bmchiul  plates.  c^=  centrn.iorsal. 

->«  tl.e  otJ,er  ),au,I,  ,„„ch  more  str„u«ly  .levelm,e,l  .,,,,1  .t      > 
"1  mtimate  aasociatiou  with  the  ch^imhe,  "  •  ""''' 

«"m,,lex-,a,  is  show,,  i„  Fi/252    ,  i  ,  ■!'/""'«whut 

;;'">^l;  five  str„„K  cor,',s  rllial  o,  ,f  ^.l  ,  ^  1^;?  ^f™' 
""■  plates  of  >vl,iol,  these  are  compose  B  tj',  '^  "'"""^ 
K;u.f-l.o«-oells  enter  into  the  comn, Litio,,  of  f  *"'' 

;;.«.  ami  a  oo,„plioate,l  »,stem  o  I  ™,,:L  ^s^  V'"' 
'!«  central  portion  branches  are  also  sen    to  ^hf  •  ,' 

K..  abh.  in  s.,.,^e„  forms   .  brand  trverles  t ,:'™;;: 
'"■'  "*  ""  ""'"''  ""--.'a-yi^K  prolonsations  of  the  ^.dtLi 


550 


INVERTEBRATE  MORPHOLOGY. 


of  the  chambered  organ.  The  terminal  branches  of  the  radiul 
aboral  nerves  pass  to  the  integument  of  the  oral  surfaces  of 
the  arms  and  to  the  muscles  which  unite  the  various  plates, 
so  that  the  system  governs  and  coordinates  the  movements  of 
the  arms  and  pinnules  as  well  as  of  the  cirri.  The  epithelial 
system,  on  the  other  hand,  controls  the  movements  of  the  aiii- 
bulacral  and  oral  tentacles,  stimulation  of  it  causing  move- 
ment of  these  structures  in  the  immediate  viciuit}'  of  the 
region  to  which  the  stimulus  is  applied. 

Another  system  of  nerve-fibres,  consisting  of  a  perioesoph- 
ageal  ring  which  sends  off  two  branches  to  each  arm,  one 
lying  on  each  side  of  each  of  the  ambulacral  grooves,  and 
which  is  connected  with  uerve-libres  passing  from  the  dorsal 
organ,  has  been  described  as  occurring,  but  its  signiticauoo 
has  not  yet  been  satisfactorily  determined.  No  special  sense- 
organs  occur  in  the  Crinoids. 

The  reproductive  organs  are  developed  for  the  most  part 
in  the  pinnules,  occasionallj^  a  slight  development  of  tiieiii 
appearing  in  the  arms  or  even  in  the  body  proper  ;  in  llolopnn 
ahme  they  are  confined  to  the  arms.  They  consist  of  tubes 
lined  with  germinal  epithelium  on  their  inner  surfaces  and 
enclosed  within  a  prolongation  of  the  coelom.  They  lie  be- 
tween the  two  ccelomic  prolongations  of  the  arms  already 
mentioned,  and  though  the  reproductive  organs  are  develoj)ed 
only  in  the  pinnules  as  a  rule,  nevertheless  each  genital  tube 
or  raehis  (Fig.  251,  gr)  can  be  traced  through  the  arm  to  the 
body,  where  it  terminates  in  connection  with  the  dorsal  organ. 
In  their  develoi)ni(nit  indeed  they  grow  out  from  this  oi^an, 
and  it  seems  prcjbable  that  the  (jva  and  spermatozoa  mother- 
cells  migrate  out  from  it  along  the  rachides  to  reach  matuiity 
in  the  pinnules.  Comparing  this  with  the  condition  in  other 
Echinoderma,  it  seems  clear  that  the  so-called  dorsal  oi^an 
of  the  Crinoids  is  homologous  with  the  ovoid  gland  of  tlie 
other  forms.  The  reproductive  elements  i)ass  to  the  exterior 
by  one  or  tw(^  ducts  connected  with  each  reproductive  mass- 
the  origin  of  these  ducts  is  unknown. 


Tlie  Crinoids  seem  to  liave  been  closely  related  to  two  groups  of  lonib 
known  only  as  fossils.  These  were  the  Ci/stohl,i,  which  apiJeur  in  the  Lkwci 
Silurian  rocks  and  die  out  in  the  Carboniferous,  and  the  Jilantoids,  wiiicii 


TYPE  ECIIINOBEliMA. 


651 

nppear  in  the  Upper  Silurian  and  also  disannear  in  fT,.  r  i  •. 
For  a  description  of  these  fonns  roforcnceSl'vuf^to  Jh^^^^^^^^^ 
works  on  Pa]a3ontology.  On  account  of  their  sim  l.dt  v  f^r>  f  l  r  1"^''^ 
have  been  associated  with  them  in  the  cl  ,s  '^  ^  ^  *'  '  ^"""^^'^  ^^'^^ 
.l.e  groups  fonnod  an  order  "^1  i',;^::"^^;'  ^''  ^^'-'^  -h  of 
eoncerned  only  witli  recent  forms  if  .'  .  ^  '  '  ""  ^"'""""^  "'"'"'^  ^^ 
.•egard  the  Crinoid.s  ."a  c,L^        '        "  '""  ""^'^'"^  "^"^  —"-"t  to 

Tlie  class  Crinoidea  has  been  divided  into  two  nnl,.,.^      ti      r>  , 
mda^  chiefly  Pala-ozoic  forms,  eharacteriz   hn^inei.v      ?'  H  '^'''''"■■ 

"uder-basals  and  of  a  series  of  nl.,f  »'»^'l>all}  by  the  presence  of 

Pletely,  to  which  u,ay^      d  ed  t     'u  IZ^f  "^  f'  '''^  '^''"^^  ^- 
...ater  wldn.  of  one  of  the  inte    .:        ,  r^^^;;  ./'ir"'''^  '''''''' 
(-0  Fig.  .50).     TbeiV.0...,,,  on  tl.  olhe    ,1      '  ,^, ,11:,^"-^ 
lonns.  te  group  making  its  first  appearance  in  tli"  M  "^"^^  ,  '^  "r 
acterized  by  the  disk  bcin.r  n.,i,r  ;.„.     ,.    .,  'Hl.sozoic,  and  is  ciiar- 

nnder-basa^  and  inti^hlds  ^  g^X  rl^r^::;  '^  ^'^^If'  ''  ''^ 
width.  Transition  forms  between  t  it  l  "  o  s^^^  ™^  '''  ^^"^'  '" 
genera  H>,ocnnas  and  Ca/a^.ocnV...,  f<,r  cCn  1  ,  '  T'""'''  *''" 
i'aheoerlnld  peculiarities  combined  with  N.  ei  Id^s  'r^"'  '"'"^ 
satisfactory  to  divide  the  class  into  families  only  leavh;.:      /  T' 

question.  ^ '  '^'^^ '"»  ""^^''"^  "ut  of  the 

Development  of  the  Crinoids.—Antedon   is    tl.P   nni     n  •     • ,      , 

-l-olopment   has  been  studied.     The  In.n^o  lead^        '  "^"""^  "''^^^ 

tor  a  time  a  free-swimming  existence,  and  possesses 

a  somewhat  ovoidal  form  (Fig.  253)  with  a  tuft  of 

01  la  at  the  smaller  anterior  end  and  five  rings  of 

ciiia  surrounding  the  body.     Not  far  from  tl.e  ante- 

'•i<.r  end  ,s  a  slight  groove,  and  lower  down  uiwu  the 

.side  IS  a  much  larger  one.     This  larva  settles  down 

upon   tiie  anterior  end,   the   slight  depression  near 

>liis  end  serving  as  an  organ  of  fixatl.,,,,  and  then 

a  rather  remarkable  rotation  occurs,  the  large  groove 
•sii-fting  round  together  with  the  interior  organs  until 
It  comes  to  lie  at  the  free  end  of  the  organism,  and  at 
1 10  same  time  its  lips  unite  so  as  to  enclose  a  cavltv 
tl)o  vestibule.  Calcareous  plates  have  ere  this  de- 
veloped in  the  connective  tissue  of  the  embryo  and  ^^^^^^ 
outhne  a  stalked  Crlnoid  into   which  the   larva  is^io.  SSS.-Lauva  of 

gradually  transformed,  the  larval  skin  shrinking  as      ^^'■''- 

>t  were,  so  as  to  closely  surround  the  stalk  and  calyx 

Wilde  the  vestibule  opens   to  the  exterior    by   the 

,^nidual  thinning  and  final  disappearance  of  its' roof 

lis  floor  forming  the  ectoderm  of  the  disk      A  ft,.,-  nr.lr     •       ■ 

»».ue  time  .,  „  stalked  Cri„„id,  t      ;   , t,  aIi^TZI  '""T";  "" 

.!.<  stalk,  a„d  thereafter  leads  a  free  Listenec"  ^     '""'"''■'  '™ 


Antedon  (combination 
of  figures  by  Thompson 
AND  (ioETHK  after  Koii- 

SCHELf  AND  HeiDERJ. 


552 


INVEHTEBRA  TE  MOEPUOLOO  Y. 


II.  Class  Astekoidea. 

The  Asteroidea,  or  Starfishes,  are  all  flattened  forms,  at 
no  period  of  their  lives  attached  by  a  stalk,  but  creepinj^r 
about  freely  upon  the  oral  surface.  In  some  forms  the  Ixxlv 
is  a  flattened  disk  pentagonal  in  outline  {Asterina),  but  Uh  m 
usually  (Fig.  246)  the  Ave  radii  are  prolonged  out  into  live 
stout  unbranched  arms,  and  in  some  forms,  such  as  Brisimid, 
the  arms  may  be  long  and  slender  and  more  than  five  iii 
number.  The  mouth  is  situated  in  the  centre  of  the  oial 
surface,  and  the  anus  slightly  excentrically  upon  the  aboral 
surface,  while  the  hydiocoil  system  of  tubes  is  confined,  as 
in  the  Criuoids,  to  the  oral  surface  of  the  body,  except  tliat 
the  madreporiform  tubercle  by  which  the  system  comniuiii- 
cates  with  the  exterio?  ipou  the  aboral  surface  in  the  iu- 
terradius  CD. 

The  ectoderm  is  throughout  ciliated,  and  contains  usualh 
numerous  mucous  glands,  while  in  its  lower  laj'ers  ganglion- 
cells  and  nerve-fibrils  form  a  plexus  extending  over  the  entire 
surface  of  the  body. 

Calcareous  matter  is  deposited  in  the  connective  tissue, 
but  in  the  majority  of  forms  the  primitive  apical  plates  are 
not  recognizable  iu  the  adult;  more  usually  the  aboral  !<ur- 
face  is  covered  by  a  large  number  of  small  plates  arraijgt,'d 
without  any  regularity,  or  else  the  calcareous  matter  furiurt 
a  reticulum  composed  of  numerous  fused  bars,  short  spines 
rising  frequently  from  the  points  of  union.  In  embrvos, 
however,  and  in  some  adult  forms,  such  as  Zoroaster  vl'i;;- 
247),  the  apical  system  can  readily  be  made  out,  and  euu- 
.siscs  of  a  centrodorsal  plate  (Fig.  247,  CD),  sometimes 
grooved  upon  the  edge  for  the  anus  (an),  surrounded  by  tive 
under-basals  (2)  usually  small,  alternating  with  which  are 
five  basals  (3).  At  the  base  of  each  arm  is  a  radial  (4),  aiul 
in  embryos  beyond  this  there  is  in  each  radius  another  plate. 
Avhich  as  growth  takes  place  is  carried  further  and  further 
from  the  radial  and  finally  forms  the  terminal  plate  (J)  of  the 
arm,  by  which  name  it  is  known. 

Of  the  oral  system  the  orals  are  possibly  represented  by 


TYPE  BOUmODEUMA. 


e-seutt--*]  bv    ^ 


853 
ti.e  so-called  ocl„ut„,,hore  plates,  ,vi,ici,  are  geuerally  s,„..II 
..Kl  m  ,„a„y  ca«e«   covered  over  by  otlu-r  plates  „f  (L  t! 
-..■tace,   ami   lu,    iu    the    ™,„e.liate    ueigl'borhoo.I    of  the 
"ou  h.     At  the  juuctiou  of  the  oral  and  aboral  surfaces    f 
he  d.sk  and  ar,us  two  series  of  plates  are  frequently  to  be 
l.nmd  wlach  from  their  p„.,itiou  are   ter,„ed  the  sJprn.ll 
,«/,•«.»<,,  nnals.  and,  in   addition   to  these,   series  of , dates 
yth  dehude  arransen,ent  are  developed  iL  conneo  i  .^      , 
he  vater  vaseu  ar  system.     Thus  along  each  side  of  the  n 
.  le  hne  of  each  arm  is  a   series  of  plates,  which  slo       , 
aborally  and  towards  the  axis  of  the  Irm,  meet  to    o.^^     t 
auor  of  an  amb„lacr,.|  groove  which  extends  outw,   ds  from 
l.e  mouth  to  the  extrendty  of  the  arm      These  are  th. 
yiacral  pluses  (Fi,,  25i,  A,  and  each  series  or^^rLtnW 
"l-u  the  outer  side  by  a  row  of  a,l.,M,o,-al,  ^^  ^t 
"Lose  number  may  ,n-  may  not  correspond  with  tl^U  ol  th, 
ambulacrals.     Between  the  adan,bulac'ral  series  of     .itn 
».i"^  a  series  of  plates  may  be  interposed  upon  the  o "a  s'r 

;:::bi:;:;i;!f ''-'■--- '-^  of\..,a;::"x 

Spines  are  very  frequently  borne  by  the  plates  or  reticu 
...  "1  the  aboral  surface,  but  are  usually  low  and  in>  n  v" 
e.  though  upon    he  marginal  and  adan.bulacral  plate    t" 
H.e  very  frequently  longer,  united   to  the  plates  byT  rudf 
...en ta.7  articular  surface  and  supplied  with  muscle  fibres  b! 
«  .  oh  they  can  be  n.oved.     In  addition  to  these  append-  „es 
..1  the  dern,a    skeleton,  others  are  to  be  found  in    he  8^., 
W.es,  such,  tor  example,  as  the  ciliated  spines  found  i    " 
le.-  forms,  such  as  Z«fc,  upon  the  margin  d  plates      These 
^.mes  are  small  and  delicate,  and  gro,';ped  togelher    ^e 
I....e.pal    pecuhanty   being   that    thev   are   covered  by   an 

;        e^^ium  ol  h,gh  columnar  cells  which  bear  strong     ,ia'    l" 
.o.-t  bta.hsh  also  peculiar  structures  termed  pedlcelhru,  are 
.•veloped  in  connection  with  the  skeleton,  but'^theb  de^,-; 
on  may  be  deterred  until  the  Echinoids  are  under  di'cu 
......a  winch  group  they  reach  a  high  ,rade  of  d  t  ,  ,. 

.  u.t.     lecu  nir  to  certain  genera  of  Starfishes,  e.g.  /.«,/ 

tl.e  body.     1  hey  consist  of  small  columns  of  carbonate  of 


I 


\^- 


IMAGE  EVALUATION 
TEST  TARGET  (MT-3) 


4 


sr  J^    MP., 


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1.0 


I.I 


1.25 


i^g^  12.5 


•S  m 


ut 

u 


11^ 


2.0 

1.8 


U    nil  1.6 


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W- 


^  #  -%  ^>^ 


w 


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m 


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Photographic 

Sciences 
Corporation 


33  WIST  MAIN  STRICT 

WIMTII.N  Y.  I4SI0 

(>i»)  ^73-4103 


4ss 


^ 


654 


IN  VERTEBRA  TE  MORPIIOL  00  Y. 


lime  imbedded  iu  the  coune(3tive  tissue,  aud  bear  upon  tlieir 
free  extremity  a  number  of  radiating  spines,  which  vary  in 
the  amount  of  movement  of  which  they  are  capable  iu  ditrcr- 
eut  species.  Tlie  paxilla  are  frequently  found  iu  grou})s 
around  the  dermal  branchijB,  over  which  the  spines  may  bo 
bent  so  as  to  serve  for  protection. 

These  dermal  branchije  (Fig.  2o4,  h)  are  pouchiike  evagi- 
uations  of  the  coelomic  cavity  with  thin  walls  composed  of 
ectoderm  and  a  layer  of  ciliated  cells  continuous^  with  the 
peritoneal  lining  of  the  cfeloni.  between  these  two  layers 
there  bein^  but  a  slight  developuient  of  connective  tissue  "and 


Fig.  <i5-t.— Tkansveuse  Section  of  Aum  ok  a  Staufisii  (.nodifled  from 

LuDwio). 


A  =  ambuliicrul  plivte. 
am  =  umpiilla. 
an  =  iiboiiil  nerve. 

B  =  adiiinbiilacral  plate. 

b  =  branch  ia. 

c  =  digestive  cojcum. 

ec  =  ectoderm. 


I  =  scbizoccclic  siuus. 
mn  =  iiiuscvilar  nervous  system. 
N  —  epithelial  nervous  system. 

0  =  ovum. 

p  =  peritoneal  epithelium. 
pi  —  calcareous  plate. 
rh  =  radial  hydrocHcl-vessel. 


If  =  tube-foot. 

circular  and  longitudinal  musch^-libres.  These  pouches  arr 
scattered  plentifully  over  the  aboral  surface,  aud  in  soiuf 
forms  occur  upon  the  oral  surface  also.  Their  thiu  walls  -auA 
the  extent  of  surface  they  collectively  represent  leave  little 
room  for  doubt  but  that  they  possess  respiratory  functimis. 
though  they  may  also  serve  indirectly  in  excretion,  since  it  li.i> 
beei'  asserted  that  the  amceboid  cells  of  the  coelomic  Lain  - 


TYPE  ECIITNODBUMA. 


555 


iiodifled  from 


^'^  :'r::- r^r -:  ™tt;; :  -  r-'-  "-« 

''■■"•eve...  n  det.n«,  .lescipti,;,  "si  , ft  s"  ""/,  """"■''■ 
ra.lial  ciocmu  „f  the  (li.rpsliv,.  f..     ,  ,  "  •^''■>'  ""»»  each 

»i.ieh,  wi,l^tl,eL^    ,"';«''"'•'''■■''  "--'enes  (Fi,,.  ,,i, 

sti-oiiK  wall,  ,vl,ioh  i.s  i„  e„n„„n„  .       "'  '"•""y  '''"■'< 

l'"rti"u  of  ti.e  ocBlom  wlrcl,  i.  1    r  •"""•"■     ^''"»  "  "■ 

;;■■ .;  ".e  e,„.,,o  :,:^;:lx'i:r:r  r-'  "■«  ■-'• 

' .«!.  .•...lain  s|,,„.,.;X,',''^r ','''"''  '"  ""•  ^»'e'-'"<le«, 

--""«-i.,.  a.;  ,,..;!r,;;l;;,,:;;;;- ;u.- ..a^ 


656 


IN  VEHTEBIiATE  MOIilVIOLOG  V. 


glaud  iij  formed  of  loose  conuective-tissuo  trabecnljo,  whicli 
are  covered  by  cells  frequently  fouud  iu  active  division,  and 
are  supposed  to  become  the  auujeboid  corpuscles  of  the  ca'loiu 
and  blood  system. 

The  hydroctel  consists  as  usual  of  au  oral  riu<^  and  i'lyo 
radial  canals,  the  latter  lying  at  the  bottom  of  the  ambulacrnl 
grooves  and  therefore  external  to  the  ambulacral  plates  (Fig. 
254:,  rhy    Between  each  pair  of  plates  a  branch  passes  upwards 
(i.e.,  aborally),  and   dilates  into  a  globular  sac,  the  ampulla 
(Figs.  254  and  255,  am),  Avhich  is  occasionally  double,  .-md  from 
this  a  cylindrical  tentaclelike  process  passes  outwards  again 
between  two  plates  forming  extensible  processes  (Fig.  254,  Ih) 
equivalent  to  the  tentacles  of  the  Crinoids.     These  processes 
in  some   of  the   more   primiiive  forms,  such  as  Lvidia  and 
Ast t'opecten,  and  tlie  terminal  ones  at  the  extremity  of  the  arms 
of  all  forms,  are  conical  iu  shape,  but  more  usually  the  groat 
majority  of  them  are  provided  at  their  extremities  with  suck- 
ing disks,  whereby  they  can  adhere  to  foreign  bodies  and  siu'vo 
thus  as  locomotor  organs.     Hence  they  are  known   as  tlio 
tube-feet  or  ambulacra.     In  some  forms  they  are  arranged  in 
two  rows,  t)ne  on  each  side  of  the  axis  of  the  arm,  but  in 
others,  as  for  exami)le  the  common  Stariish  Asferia.s,  the  suc- 
cessive feet  of  each  row  alternate  with  each  other,  so  that  tliev 
have   the   ai)pearance  of  being  arranged  in  four  rows.     ]>v 
means  of  the  muscles  of  the  wall  of  the  ampulhe  water  can  be 
forced  into  the  tube-feet,  which  may  be    thus   extended,   a 
circular  valve  occurring  in  the  branch  which  passes  from  the 
radial  canal  to  the  ampulla  preventing  the  water  from  })assing 
back  into  the  canal     Contrary  to  what  occurs  in  the  Crinoids, 
there  are  several  ai)pendages  to  the  oral  ring,  iu  addition  to 
the  stone-canal.     This  leaves  the  ring  iu  the  interradius  r/> 
and,  passing  abovally,  communicates  with  the  axial  .sinus  wliieli, 
as  already  stated,  opens  to  the  exterior  by  the  madrei)orite. 
This  isacom])licatod  calcar(>ous  sieve.plate  of  some  thickness, 
and  the  union  of  the  canal  and  the  sinus  takes  place  wilhiii 
its  substance,  so  that  in  r(>ality  the  canal  seems  to  open  to 
the  exterior.     The  embryonic  history,  and  the  fact  that  injee- 
tions  forced  through  the  tubercle  pass  into  both  the  sinus  nnd 
the  canal,  shf)w  that   what  has  been  described  is  the   true 


TyPM  KClllNoDKttMA. 


657 


H-'la  .o„8l.,i,.      I„   ti,e   w.lls  „f  tho   st„„o-c,„,al   culearooas 

the  surface  „.■  the  ciliate.l  „,,it,,„,iu,„  ,,„i„,.  th„„  iu^-ea.".!    ' 
Ihe  „,,,,o„,laHe.s  „t  the   oral  riu„  are  of  t«-o  kinds,  both 
he,„«  situated  m  the  iuto>>-a,lii,  that  coutaiuiu;.  the  stoueia," 
howevo,,   usually   lacki,,.,   any   other   appe^da^e.    T,     s t  e 
l-n,s   hollow  saclike   struc:ures   opeu  'iiuo  the  ri.,«   by 
..."•nnv  uock.  and  are  termed  the  Polian  vesicles;  thc^Ir  walls 
-msist  of  conuective  tissue  iu  which  are  situated  n.uscle 
hlnes,  and   theu-  interior  is  line.l   by  an  epithelium  wh  „I 
appears   „  separate  and  fjivo  rise  to  tho  an„eb„id  cells  of  the 
|."l.-oc,„l  1  ,„d.    The  other  kind  of  appendages  occur  generally 
throu^.hout   he  group  and  are  know,i  as  Tiedemau's  vesicles 
c"..s.st,n(;  „   n,asses  of  hollow  tubes  arranged  iu  pairs  iu  oae 
;;;■  --  <>'  '!»>  ".ter..adii.     Tho  epithe.iunHining  'tl.e  wall    o 
icse  s  rm..tures  als„  .  en,s  to  .-ive  rise  to  the  a,„,eboi,l  cells, 
I  ..tl,  k.mis  ol  organs  l,e,„g  tuerefore  comparable  to  Iv.nphntic 
«lands,  though  the  l-oliau  vesicles  have  also  been  regard         ! 
reservoirs  lor  the  hydrociel  Hi.  id.  " 

The  „n,»th  is  situated  at  the  centre  of  the  oral  surface  of 
he  disk  and  opens  into  a  short  .esophagus  which,  i„  some 
Tonus,   has  connected  with  it   ten  glanduhir  pouches.     The 
...sophagus  opon.s  iuto  a  usually  capacious  car.liac  stomach 
"Inch  is    re,,ucntl.y  lobo.l  (l-ig  2.55,  c),  is  ovorsible  and   pro. 
vMlcl   with  specnil  muscles  for  its   retraction.     Above    his 
"unes  the  pyloric  stoma.d,  which  gives  rise  to  Hve  radial 
P-uches,  which  son,,  branch  into  a  pair  of  sacculate,!  pouches 
«e."."g  out  into  the  arm,,,  an.l   being  termed  th'e  radial 
la     ).     From  the  p.vloric  stomaoh  a  short  rectum  passes 
.'l>.Mally,  mterra,l,al  ««„a  being  .somotimes  found  close  to  its 

w'l  ll  ?''■■  "™  "'"'":■''•'""•  "!>«.«  upon  the  dorsal 
^  "face  In  a  few  forms,  such  as  /.Mi,,,  .-(.,/,,,,,..,„„,  and  their 
•Nhes,  the  anus  ,s  wanting,  but  more  usually  it  is  present  iu 
till!  r(><,M()ii  indic'uted. 

The   epitliolial    norvous   .svHteni   consists   of   a  i,lexii8  of 
K.iu^'  lon-ce  Is  a.ul  fthros  i.abod.lecl  in  the  ectodern.  and  cover 
mg  the  siirfaco  of  tlio  l,o,Iy.  and  of  an  oral  rin«  and  Hve  ra.'ial 
nerves  (Fi,.  254,  S)  which,  as  in  the  Cnnoid^are  siti;a;;;:;  • ! 


658 


IN  VKHTMBIiA  TM  MOUPIIOLOG T. 


the  lower  liijers  of  the  ectoaerm.  Upou  the  aboral  siirfaco 
of  the  oral  rill-,'  and  the  radial  nerves  sections  show  distinct 
bands  of  fibres  separated  from  the  rin<r  and  uerve.s  by  a 
d'dioate  hiyer  of  connectivo  tissue  ;  these  constitute  the  nius- 
cular  systoun  of  j.erves  (Fi<r.  25^  mn\  ami  their  branches 
appear  to  b(^  supplied  to  the  muscles  of  the  body-wall  and  of 
the  ampuihe  and  tube  feet.  Tiie  aboral  system  is  but  feehly 
developed  when  compared  with  that  of  theCrinoids.  A  trans- 
verse section  of  an  anil  sIh.ws  lyin-;  between  the  muscles  ..f 
the  aboral  surface  and  the  peritoneal   mesoderm  u  cord  of 


Fig.  255.— a  St.vhfisit.  Asternranl/iion.  with  tuk  iNTKOtrMisNT  or  tiii.;  disk 

AND  KAYS    UK.MOVKl)   To    SHOW   THK    IKTIUUNAI,    STIIUCTUlll!;. 

"'  ~  '""'^  ff  =  reproductive  orgau. 

nm  =  ampulla!  of  tiibo-foet.  I  =  Hvor  ciucu. 

(10  =  aiubulucnil  ossicles.  M  =  madreporito. 

c  =  cardiac  poiicli  of  stomach.  A-E  =  tljc  live  radii. 

nerve-fibres  (Fij^.  254,  an),  the  five  cords  (•onv(M-oiiifr  towards 
the  centre  of  the  aboral  surface  of  the  body,  the  entire  system 
formin<j;  thus  ji,  five-rayed  star.  In  position  and  f^^^neral  I'cl.i- 
tions  this  system  of  nerve-cords  is  directly  comparaI)le  to  the 
aboral  system  of  the  CIrinoids,  and  may  be  regarded  ;is 
homol()j;ous  with  it. 

Special  sense-organs  are  re])resented  by  the  terminal  leii- 
tacles  of  the  radial  hydroccel  canals,  which,  as  already  stafe.l. 
retain  a  teutach>-like  form  and  do  not  d(n-elop  suckers  a(  the 
extremity.     Their  walls  are  richly  supplied  with  nerves,  .md 


TYPE  EVIIlNODEIiMA.  ggQ 

they  ure  surrouude,!  mid  nmy  be  c(,voiecl  in  by  the  movable 
spiues  „t  the  iulHinbuhicnil  a.ul  i„ai-inul  plates.     That  thev 
have  a  sensory   function    se.mis   ch'ar,   Init   what   the  evaJt 
nature  of  the  function  nnty  be  is  as  yet  uncertain.     At  the 
base  of  the  terminal  tentacle  of  each  arm  is  situated  an  eye 
<'<>UHist.n^  of  a  laroe  number  of  conical  depressions,  lined  bJ 
an  ep.thehum  contaiuiuK  a  red  pi^Mnent,  covered  on  tlie  out- 
side  by  a  cutich.  and  ri<d.ly  supplie.l  with  nerve.fil)iil,s.    There 
do  not  seem  to  be  pr<,sent  any  refractive  structures  other  than 
tlu>  cutich^  and  these  eyes  can  only  c..nvey  to  the  aninnil  im- 
pressions of  chanoes  in  the  intensity  of  the  lij^bt  fallin.^  upon 
them  ;  they  cannot  form  ima-es  of  external  ,d,jects 

Th.^   repro.luctive  o.-^^ans  are  ten   in   nund.er,  two   beiii.^ 
situated  in  each  arm  (Fio..  2.15,  .,).     Eaeh  consists  of  a  mass 
ot  roproductive  cells,  and  is  enclosed  in  a  genital  sinus  (Fi... 
-.;.4,  I),  winch,  as  already  stated,  communicates  rith  the  axi^l 
sinus.      Ihe  proximal  end  of  each  gland  is  connected  with  a 
<-;dhke  structure,  the  genital  eor<l  or  rachis,  the  ten  cords 
u..iting  m  a  ring  situated  beneath  the  aboral  surface  .,f  the 
iH'dy,  a  c,,rd  passing  orally  from  this  ring  to  unite  with   the 
tissue  of  the  ovoul  gland.     The  genital  sinuses  accompany  the 
cords,  enclose  the  ring,  and  pass  to  the  axial  sinus  along  with 
h(^  descending  cord.     A  connection  therefore  exists  between 
[h;  repro.luctive  organs  and  the  ovoid  gland,  just  as  in  the 
Cnn.nds    and   indeed   the   reproductive   organs   ari  e   in   the 
ombryo  Ironi  an  outgrowth  of  the  ovoi.l  glan.l.     In  reality  the 
genital  cords  are  tubes  containing  in  their  interior  iMinuIture 
rnprnductive  cells  which  seem  to  migrate  from  the  ovohl  gland 
to  the  re,)roductive  organs  where  they  become  mature.    -The 
vn]m)duct,ve    openings    are  usually  placed    upon  the  aboral 
surface  {Asfnn,n  forming  an  exception)  of  the  arms  or  disk  in 
the  interra.li.  ;  a  single  pore  usually  exists  for  each  gland 
ami  o(!casionally  there  may  be  several. 

r)evelonm'nt,,ftJ,e  Asteroulca.-lU^  ],,.val  forms  of  tho  Srarflsl.es  -iro 

..own  as  th..  m^innana  an.l  BnH,Mana.     Tl...  formor  l....s  a  s  .    ,  'wl  u 

n:u.«u  u-  sl.,H.   H..  .,.x  of  ,1..  tnan^lo  l,oin,  tl.  ann.-io    .^^     I.:  "' 

a...l   a  ,i...  and,  I.,  ol  the  ventral  s.n-fac..  is  a  .l.op  concavilv  in  vvhid     i ,'. 

•-..1.  o,u.ns.     Th.  posterior  l,..nle,.  of  ,he  con.^ity  is  rorn.e,    ^  ,  a 

ot  ul.a  wind.  ,s  eontinue.l  around  the  lobe.l  .sides  of  the  l,o<lv  to  t   e 


660 


JN  VEUTEBHA  TE  MOliPIIOLOO  T. 


V 


tonor  extremity,  forming  a  postoral  ciliated  band,  the  anus  lying  witiiout 
the  area  enclosed  by  it.  In  front  of  the  mouth  is  a  trilobed  region  also 
surrounded  by  a  band  of  cilia,  the  adoral  band.  In  young  embryos  ti,. 
adoral  and  postoral  bands  are  united  at  the  apex,  separation  only  suj.,,- 
VM.>ning  later.  In  later  stages  two  additional  arms  are  developed  at  the 
sides  of  the  apical  lobe,  which  becomes  like  the  new  arms  destitute  of  ciii  i 
and  tipi)ed  wiLh  a  group  of  wartlike  elevations.  This  form  of  the  larvi  'i  ■ 
known  as  the  limchiolaria.  '     '    '^ 

A  peculiar  process,  amounting  almost  to  a  metamorphosis,  occurs  durin.r 
the  translormation  of  the  larva  into  the  Starfish.  Calcareous  plates  of  the 
aboral  system  make  their  api)earance  on  the  dorsal  surface  of  the  stomich 


Fig.  256.— Btpinnatiia  ow  Asleracanthion  (after  Aoassiz) 
an  =  anus.  ],,,  =  i.ydn.ca'l.  m  =  mouth. 

near  the  posterior  end  of  the  body,  and  oral  plates  on  the  ventral  surfa.  .> 
o.  the  same  organ.     The.se  two  systems,  at  first  rather  widely  senan.l'ni 
gradually  approach  each  other,  and  at  the  same  time  the  iutonvA  or....K 
assume  the  adult  form.     Finally  the  two  series  of  plates  unite,  encl.rsin.^ 
between  (hem  the  hydroccel,  a  portion  of  the  digestive  tract  an.l  of  tlH>  n.^. 

"";  ,J  .  T'^?''^  "'""^''  •'""^  '"■•"'  •'"«  obliterated,  and  indeed  the  anl.r- 
lor  half  of  the  larva  takes  no  part  in  the  formation  of  the  adult  animal. 
but  IS  gradually  absorbed. 

A  highly-developed  faculty  for  regeneration  occurs  in  the  Asteroid,;,. 
the  disk  being  able  to  regenerate  lost  arms  ;  and  indee.l  an  arm,  with  wi,i,li 
u  small  fragment  of  the  disk  is  in  connection,  has  the  pow.>r  of  regeii.w.il- 
ing  all  the  missing  parts.  Specimens  of  the  eommeii  Starfish  Ast.na.s  ar," 
in  consequence  frcpiently  found  with  one  or  more  of  the  arms  bifid  a(  il- 
tip,  or  even  with  an  abnormal  number  of  arms, 


tW^'--'- 


TYPE  ECIIINODEIiMA. 


661 


III.  Class  Ophiuecidea. 


.•.oI';^"';;::;:?!?,::;,7,,;^f ':-'•"■«.  -emi-e »,« starfishes 

i"  -ill  cases  slH,„Ier  a,„l  HsH,,:  ^'  "'■"'"'  ''"»"'^'»-'  »'«> 


y  10.  257. -Op/iioffh/pha  aculeatu  from  tiw  AT.on*T   «r. 

I^KKs..^K^.  A.C..  z^:::\^:::^^ '"  ^"^^  ^"•^ 

(Th...  arms  are  cut  oil  close  to  the  disk) 
1  =  centioilorsal  plate.  .. 

3  =  under  basals.  =  ''"'"*'«• 

4  =  ladials. 

face,  there  are  no  visible    nmlmlnnvni 

-liicl.  a,e  move,,,.  Ins    'i,™       ■  f"™',""  "'^  """«• 

t»iu  e,.oal  processes  ,>f  tl  e      t  .  i     .i;  T"  T'll'"  "'"'  '"■"■ 
each  side  of  each  of  the  fiv»  ?   ,     !,  '     ^'"'•""'"""■•e,  o., 

tlic  oral  surface    ,    t       ,,1  k    'mii      "  "  """"  "'"  '■''«"  "' 

;» the,  a,.e  ^^U'z  a:'z:::^\:'z!':::::jr- 

liey  seen,  to  have  a  respirat,,,.,.  f„„„tio„   .„T  """"/"'■"«• 
''"■  «it  of  the  ,.e„.„a„ctile  el^^ent::,',' ;:;,:e"fors:et  l^X 


662 


INVERTEBRATE  MORPHOLOGY. 


phiura  squamata,  even  serving  as  brood-pouelies  in  which  the 
young  develop. 

The  ectoderm  is  indistinguishable  over  the  greater  portion 
of  the  body  in  the  adults,  becoming,  as  in  the  Crinoids,  con- 
founded with  the  mesoderm.     Calcareous  plates  are  largclv 
developed  iu  this  tissue  (except  in  Ophiomyxa  and  its  allies), 
giving  to  the  disk  and  arms  a  brittleness  which  has  suggested 
the  popular  name  for  the  group.     The  extent  to  which  the 
apical  system  of  plates  is  distinguishable  in  the  adults  varies 
considerably  even  in  members  of  the   same  group,  and  while 
in  some   forms  (Fig.   257)  all  the  plates  represented  iu  the 
{Starfish  Zuroader  can   be  distinguished,  in  others  only  the 
radials  or  the  basals  or  both  are  visible.     At  the  tip  of  each 
arm    is  a  plate    comparable    to    the    terminal  of   the  Aste- 
roidea,  and  iu  addition  there  are  frequently  present  series  of 
interradials    or    interbrachials,    the    most    aboral    plates    of 
which  separate  the  radials  from  each  other  and  extend  round 
to  the  oral  surface,  abutting  on  five  large  plates  known  as  the 
buccal  shields  and  corresponding  to  the  orals  of  other  forms. 
On  the  aboral  surface  of  the  disk  above  the  origin  of  eacli  aim 
there   is  a  pair  of   plates  termed  the  radial  shields,  whicli 
must  not,  however,  be  confused  with  the  radial  plates  extend- 
ing ak)ng  the  aboral  surfaces  of  the  arms. 

These  latter  form  a  complete  series  extending  from  the 
disk  to  the  terminal  plates,  and  form  the  aboral  wall  of  the 
arms,  their  lateral  walls  being  formed  by  another  series  of 
plates,  the  adamhulacmls  (Fig.  258,  Ad),  while  still  another 
series,  the  superawhulacrals,  form  their  oral  walls.     Between 
each  adambulacral  plate  and  its  successor  is  a  pore  (usually 
bounded  by  a  number  of  small   plates)  through  which  tlie 
tube-feet  are  protruded,  the  radial  water-vascular  canals  being 
situated  in  the  interior  of  the  arm.     The  cavity  of  the  arms 
is  occupied  almost  entirely  by  a  linear  series  of  calcareous 
masses  termed  the  vertebral  or  amhulacral  ossicles  (Figs.  258 
and  2G0,  A\  each  of   which  consists  of  two  halves,  usu.illv 
firmly  united  by  suture.     The  ossicles  are  united  by  well-dii- 
veloped  articular  surfaces,  and  have  attached  to  them  muscles, 
whereby  a  considerable  amount  of  motion  is  possible  for  the 
arms  as  a  whole,  the  motion  being  almost  entirely  in  a  hori- 


TYPE  ECIITNODEHMA. 


11  wliicli  the 


563 


/ontal  plane,  except  in  Astrophyton  and  its  allies,  in  which 
the  arms  may  be  coiled  up  over  the  oral  surface,  in  a  manner 
smnlar  to  what  is  found  in  the  Crinoids.  These  ambulacrax 
ossicles  seem  to  correspond  with  the  similarly-named  plates 
of  the  Asteroidea. 

In  the  neighborhood  of  the  mouth  certain  modifications 
m  the  arrangement  of  some  of  these  plates  occur.  The  two 
halves  of  each  iirst  ambulacral  ossicle  (Fig.  258,  A  )  are  widely 
separated,  and  come  into  close  relation  with  the  simMarlv- 
separated  ossicles  of  adjacent  radii,  forming  a  buccal  shield 
lie  pla  e  so  formed  rests  upon  the  aboral  surface  of  the  first 
adambulacrals  {Ad,),  which  unite  in  pairs  in  a  similar  manner 


Ad  4 


Ad, 


^y^\  Ad, 

A  =  nmb„l„c™l  plates.  „  =  p.|„  ,      ,„^ 

Ad  =  adambulacrals.  y  _  to,.„g 

/  =  iutenadial.  ^  ^  „,^,  ^^^^^^^^^ 

wr  =  radial  hydroccel-vessel. 

forming  a  triangular  plate,  termed  an  oral  angle-piece,  lying  in 
an  in  erracius,  and  partly  covered  on  its  oral  surface  by  a 
buccal  shield  At  the  sides  of  the  buccal  shield  are  the  so- 
called  lateral  buccal  shields  {AcQ,  which  are  in  reality  the 
second  adambulacrals  of  adjacent  arms,  and  cover  in  the 
second  ambulacrals  (A,),  which  serve  as  supports  for  the 
oral  angle-piece.  Along  the  margins  of  the  oral  surface  of 
tins  are  a  series  of  spines,  the  hnc<^al  papilla,  while,  at  the  apex 
of  the  triangle,  are  the  dental  papillce.  The  vertical  edge  of 
the  piece  is  furnished  with  a  number  of  stout  projections  the 


504 


mveitTESBATE  iroitmoLoor. 


palm  angulares  (Fig.  260,  p),  whose  bases  severally  fuse  to 
form  a  supportiug  plate,  the  ton^  anyulm-u  (T) 

Spmes  dejeh.ped  iu  coiiuection  with  the  dermal  skeleton, 

ea™,g  out  of  ccsKleration  the  oral  a.gle-pieees,  ma,-  b    ™' 

tirely  wanting,  b,,t  lu  mauy  forms  they  are  bor^;  iu  ™,ti  '  1 

rows  „p„„  the  adambulacrals,  aud  are  usually  movable     lu 

JZZZ7'°"'''  ""?"  '■"'""""'K  ■-'^y  bottom  ,,e- 
cliai  hooked  spmes  are  situated  ou  the  oral  surface  of    l,e 

a  ms  towards  their  extremities,  and  seem  to  serve  au  ad    . 

:::  aS;:,.,:'^''"""'^  -« ""-■"'  -^' '-  -^-"^t; 

The  coelo,,,  (Fig.  2«0,  e)  is  of  comparatively  slight  e.te.t 
he  cavity  of  the  ,lisk  beiug  largely  occupied  byt^e    ige    ^v e 
t  act,  and  th.at„f  the  arms  by  the  ambulacra!  ossicles,     it 
disk  the  cavity  IS  traversed  by  numerous  bauds  which 
tend   from  the  body-wall  to  the   wall  of   the  digcstiv-e  st 
and  from  the  wall  of  the  esophagus  a  membr  nt  exteu  ^ 
outwards  and  orally  to  be  attached  to  the  peribuccal  p  ate 
forming  a  septum  (Fig  2C0,  ,),  enclosing  a  cavity  surroum ' 
n.g  the  esophagus,  the  peripharyngeal %ac,  (^  whiT  , 
completely  separated  from  the  rest  of  the  c»lo,f  \n  X,', 
thn.  and  some  other  forms  a  second  septum  occurs  pa^ 

TsZZ''Z"'T''1\T  "'*'  "'^  I'eripharyngea',:*! 
is  double.     T  e  coelom  of  the  arms  consists  of  two  portion, 
one  lying  on  the  aboral  and  the  other  on  the  oral  side  of,' 
series  of  ambulacral  ossicles.     The  aboral  cavitv  is  expand 
laterally  so  as  to  partially  surround  the  ossicles,  but  t iT  a 

lamella,  and    is  thus   separated  into  a  series    of  chambers 
Jhicb  open  into  the  undivided  aboral  portion,  term  d  th 
aboral  or  dorsal  caual.    Au  axial  sinus,  standing  in  close  r 
atlonship  to  the  ovoid  gland,  exists,  but  presents  som.tfel. 
tures  uot  found  in  the  Asteroidea.     It  consists  in  A,„p,.  Z. 

ara  ed  from  one  another;  one  of  these  is  the  so-called  aL  • 
pulla  (am)  of  the  stone-canal ;    tlie  second  (.)  lies  iu  clos 

w  u  ^hu  'r  ?™' •''"""•  ^*'"''''  ''"-'"p^''  - '"  -i 

wit    'tlT  "l        '^  '",  """'P'"-''"™'.^  -mall,  and  is  associated 

With  the  genital  cords  (;,,•),  and  the  mass  of  cells  in  the  ovuid 


TYPE  ECUINODSIiMA. 


66ff 


f^'laud  from  which  these  arise.     These  two  last  cavities  are 
.u  d  to  be  portious  of  the  general  coelom  which  become  sepa 
rated  oil  dunug  development,  and  are  not  simple  exTensions" 
ol  that  portion  of  the  ccelom  into  which  the  stoie-canal  opens 
m  the  embryo,  and  which  persists  as  the  ampulla  ^ 


am       pc 

Fm.  259.-DIAGRAM  showing  the  Relationships  of  the  Stone  can*t 
Axial  Sinus,  etc..  in  Amphiura  s,uunu,ta  (arte.- jucBrz^k,  ' 

am  =  ampii  la  of  stone-canal.  ^  ^  ri„g-nerv, 

U  =  geuital  bursa.  «_.„*,     ,'\ 

mp  =  madreporite.  ^'  =  Peripharyngeal  space. 

mu  =  muscle.  *  =  ^'""*^- 

sc  =  stoiie-canal. 

»»».  the  ..p„„a  „,  the  s.one-eanafo,  «,e  oThT^  a'^d  1:1^' 
Lying  on  the  aboral  surface  of  each  radial  nerve-cord  is 

a  adial  sclmocoehc  sinus  (Fig.  260,  br),  which  communicate' 
.th  an  oral  s.nns  surrounding  the  mouth.  The  reTatbns  o^ 
.s  system  are  similar  to  those  of  the  schizoeceli         tem  „ 

. ■  1  «  "°  r'  "'"'  "-'r'""'  »■— ictions  beLe"  it 
am  the  ccelomic  cavities  occur.  It  contains,  however  a 
sjstem  of  canals,  which  correspond  to  the  lacu^se  occurring 


566 


INVERTEBRATE  MORPJIOLOG Y. 


f  i 


iu  the  walls  of  the  oesophagus  iu  the  Crinoids.  They  huve 
been  termed  blood-vessels  in  the  Ophinroideii,  the  siuuses 
ivhich  surround  them  beiug  termed  the  perihiemal  canals; 
they  follow  the  course  of  these  latter,  a  process  of  the  ovoid 
glaud  coming  into  connection  Avith  the  oral  lacunar  ring. 
This  glaud  (Fig.  259,  o)  is,  as  iu  other  grou;)s,  im^tly  asso! 
dated  with  the  lacunar  system  and  partly  with  the  genital 
ap[)araius.  It  lies  in  the  wall  of  the  axial  sinus  and  projects 
into  it  so  as  almost  to  till  it.  At  ou(.  extremity,  as  stated,  it 
comes  iuto  connectior  with  the  oral  lacunar  ring,  and  at  one 
poiut  in  it!-'  wall  it  contains  a  nuiss  of  cells  from  which  the 
genital  cords  pass  cut  to  the  reproductive  organs,  accom- 
panied by  strands  of  the  lacunar  tissue. 

The  hydrocoel  has  the  usual  arrangement,  and  is  confined 
to  the  oral  surface  of  the  disk  and  arms.     The  radial  canals 
(1^'ig.  260,  wr)  lie  on  the  oral  surface  of  the  ambulacral  ossi- 
cles, extending  to  the  terminal  plate,  and  ending,  at  least  iu 
those  forms  which  have  simple  arms,  in  a  terminal  tentacle. 
At  regular  intervals,  corresponding  iu  number  to  the  ambu- 
lacral ossicles,  the  radial  canals  give  of!  transverse  branches, 
which  pass  outwards  in  the  substance  of  the  ossicles  (Fig.  2')H), 
and  make  their  exit  through  the  ambulacral  pores  betweeu 
successive  adambulacral  plates  to  terminate  as  tube-feet.    No 
ampulhe  occur  ou  these  transverse  branches,  though  a  circu- 
lar valve  oc(!nrs  just  where  each  branch  becomes  continuous 
Avith  thu  tube-foot.     The  feet  are  simple  conical  structures 
destitute  of  a  terminal   sucker,  and  do  not  therefore  serve 
for  locomotion.     Their  walls  are  richly  sup])lied  with  nerves, 
uud  iu  some  forujs  are  i)royided  witli  numerous  papdlii'  ap- 
parently sensory  in    function.     Surrounding  the  mouth  are 
';en  buccal  tentacles  (Fig.  2()0,  hi),  which  correspond  to  tiie 
first  two  pairs  of  tube-feet  of  each    radius  of  the  Astor.tids, 
but   arise    by   fine    braaches,    which    later   divide,   and   are 
directly  connected   witli    the   oral    ring-canal    (Fig.   258,  i). 
These  seem  to  be  undoubtedly  sensory  and  perhaps  olfactory 
iu  function.     Th(>  oral  ring-canal  usually  has  attached  to  it 
iu  each  interradius,  excejjt  that  in  v.hich  the  stone-c.tnal  lies, 
a  single  Poliau  vesicle  (Fig.  '2(50,  /*."),  though  iu  Oplnarlh 
two,  three,  or  even  four  vesicles  may  occur  iu  eac'a  iutcira 


TYPE  EClIINODEhMA.  5^37 

<l:us.      The  sto^e-eaua],  a.,  has  beeu  uoted   ouens  infn  . 
'•-    po.t:o.  of  the  e.lo,„,  the  an.pulla  oMre'l  ot^a^ 
■uKl  this  again  communicates   with  the   exterior    u    .  t  1 
npeaingbya  pore  phaced  in  the  adults  on    h     01 ,    ^mS  ! 
"t  the  body  in  one   of  the  buccal  shields  ;    pi^^uXfj! 
opening  is  situated  on  the  aboral  surface  o  dv      t.        •       . 

some  sijecies  tl,ere  may  be  five  tubercerCe  /,!»'■  ."    '" 
al»o  .n  other  genera,  B„ch  as  Am^Unra  aud  OphiJcpis  ^ 

.I-  axia.  sin,,,,  an.,  tl,o  „v„i,I  sla,,.,,  wMch  a^Tu^    "a™:; L"',;'"  .i'' 
«i"al,  ,n„l„,..„  a  similar  lm„sf.,™,a(io,i  of  „„.,i,i„„  wM,   ;  ^  '"' 

nils  IS  situated  (sou  Fig.  250).  '""'  ^"si^iilar 

The  digestive  tract  is  very  simple.     The  month  snar.le.l 

Tlie  oiuthelial  nervous  system  of  the  Onhinroi.lea  is  asso 
.■iate,l  with  the  general  ectoderm  i„  verv  v„„„' 
but  hao,.  sinks   into  the   cavity  .,     the',, ,;.-  rr""""' 
;;•;;•:.  ...ay  be  eo„.,.are,,  to  J  invaginatl:,;!'   d .,  le  Te'^u; 

lube  IS  formed  ly;n«  within  the  body-wall  <n.  the    '    , 
face  of  the   body,    the    ra,lial   ner -es  ,Fi'     2fi      .  """ 

*.ated  in  its  abora,  wall.     This  t:i,^'f;:mf    /  ;,  :;^:.'; 

.  ,»,  and  tlK.  cavity  it  encloses  .seems  to  be  in  reality      "" 

tiou    ol    tile  exterior,   thou'di    it    im.v   h^    „  i  •  ,■    ^  "^ 

5     .  ,  '   "'"'"n"    H'    nia>    oe   Hchizoco'Iip      'Vi,^ 

".ai  r,n«  o    the  nervous  system  is  not  enclosed    n„„  Ij 

.1...  c..n.,i,  but  icmuins  m  connection  with  the  ectodeL 

.t  the  lower  e.trenuty  of  the  ccso„ha«i,s,  being  .Lued  ll.,: 


1 1« 

1 1 


568 


INVEliTEBRATE  MORPUOLOGY. 


aborally  by  the  development  of  the  or«al  angle-piecea.  The 
radial  nerves  are,  however,  contained  in  the  wall  of  the  sinus, 
coming  to  the  surface  of  the  body  at  the  tips  of  the  arms, 
where  they  terminate  by  fusing  with  the  general  ectoderm. 
The  muscular  nervous  system  is,  as  in  the  Asteroidea,  closely 
associated  with  the  oral  ring  and  radial  nerves,  lying  on  tlioir 
aboral  surface  and  separated  from  them  only  by  a  thin  layer 
of  connective  tissue.  The  aboral  system  consists  of  a  riii.<' 
situated  beneath  the  aboral  surface  of  the  body,  from  which 
branches  pass  oft'  towards  the  reproductive  organs.  ludee'l 
the  entire  system  is  intimately  associated    with   the  genital 


260.— Section  tiiuough   an    Oimuuhan  showing  Sthuctuhe  (after 

LUDWIG), 

A  =  auibuliicial  ossicles.  0  =  moutli. 

br  =  scliizoca'lic  sinus.  p  =.  pulu  angularis. 

bt  -  buccal  teutacles.  p«  =  periplmryngenl  space. 

G  =  cuiloui.  PV=  Polian  vesicle. 
Jf  =  nuisile.  s  =  peripharyngeal  septum 

nr  =  radial  nerve.  T  =  torus  angularis. 

wr  =  hydroco'l- vessel. 

cords,  and  its  course  can  be  understood  from  a  descii))tii)ii 
of  these  structures.  No  special  sense-organs  other  than  the 
terminal  and  buccal  tentacles  and  the  tube-feet,  already  de- 
scribed, occur  in  the  Ophiuroidea. 

As  already  stated,  the  genital  cord  arises  from  a  groni>  of 
cells  in  the  wal'  of  the  o\oid  gland  (Fig.  259,  gr)  and  pusses 
in  an  interradius  towards  the  aboral  surface  of  the  bodv, 
carrying  with  it  a  jmrtion  of  the  axial  siuus.  Arrived  at  tliis 
point  the  sinus  and  cord  form  riugs,  the  aboral  nerve-ring 
lying  in  the  wall  of  the  sinus,  while  the  genital  cord  lies  in  its 
interior,  ftttnplifid  in  ifa  wnll  1)v  n  lo»p«11..  ,^t  -»-^t.. *i,-„  +i     „- 

From  the  genital-cord  ring  ten  short  branches  are  given  oft" 


{UCTUHE    (after 


TYPE  ECUmODERMA.  ggg 

P-longatif..  of  t  Lul"  St'  1""';  ''^  "-'-" 
iu  the  reproductive  poucbe"  Ci  »'  *"""''  ""''  """"« 
lobes  of  the  reDrodrtf  *^  *''°  spawuiug-time  the 

rushing  befr:c'rL:T:L,7;h:'e^ ''''°,  '"^  •""■»•»• 

.eproductive  elements  wheurtlb    !*"'."■""''  "'" 
cavities  of  the  bursm  wl,o„„    *i  'lirongh  mto  the 

exterior,  or  else  as  In' J  ^^  »ake  their  way  to   the 

From  what  has  been  said  it  may  be  seen  tl.,t  n 
Astro^Kyton  and  its  a.iies  differ  ilr^l^Z^tTZ 


FiQ.  261.— Pluteub  Larva  of  if.T^   ,    ■ 

«  =  (rs„plmgus  ^'•'"««r«M«o«  p«;.^„  (after  Fewmb) 

«=  rudiment  of  adult.  '«  =  momh. 

,    *  ~  t^alciireous  skeleton. 

™!;:b,e?/1;:i*'^,:;:™^  »™s   s„.neti„.es   branei,ed   and 

Peonliarities.     CV,„se,,ut„tirtt     b   l',;'  ■'"  "'■?"""  ""'«'' 
regarded  as  consisting  of  .1         .  ,"l''""''""i«"  "my  Iw 

ijK  ^i»'^.My.o„,  ^^nLr  ::„':•«'«:  T^r  '"''""- 

'*"<fcr,  iu  wbieh  tl,„  „/,,  "    ™.    "  "'"  «"»''et-star,  Tri. 

'"'•■"».  and  (he  Ommmm      i    1  •"'',"""''  ""''  """"   »"""»■• 


Opl,l,„le,-m„,  0,,l„;,lep!,,  Amph 


"(111,  etc. 


670 


INVERTEBRATE  MORPHOLOGT. 


Development  of  the  Ophiuroidea. — Except  iu  a  few  cases,  such  as  Am- 
phiura  squamata,  whose  habits  have  already  been  referred  to,  the  devel- 
opment of  the  young  Ophiuran  takes  place  outside  the  body  of  the  parent 
iu  the  surrounding  water  and  a  typical  larval  form  occurs.  This  is  known 
as  the  Pluteas  (Fig.  261)  and  in  its  general  form  resembles  the  Bipiunaria 
of  the  Starfish.  The  ciliated  band,  however,  does  not  divide  into  an 
adoral  and  a  postoral  portion,  but  remains  continuous,  and  the  lateral 
lobes  become  long  armlike  processes  supported  by  a  special  skeleton, 
formed  of  calcareous  rods  developed  in  their  interior.  The  mode  of  devel- 
opment of  tlie  young  Ophiuran  from  this  larva  resembles  closely  that  de- 
scribed for  the  Asteroidea. 


Class  IV.  Echinoidea. 

The  Ecliinoidea  present  greater  differences  in  shape  than 
are  found  in  any  of  the  other  groups  of  Echinoderms,  being 
more  or  less  spherical,  oval,  discoid,  pentagonal,  or  heart- 
shaped,  but  they  are  all  characterized  by  the  absence  o.^  arms, 
by  the  calcareous  plates  being  immovably  united  (except  in  a 
few  forms,  such  as  Astheno.somd,  where  their  edges  overlap 
and  they  are  consequently  movable)  to  form  a  firm  test,  uuJ 
by  a  great  development  of  movable  spines  upon  the  plates, 
whence  the  popular  name  of  Sea-urchins  usually  applied  to 
members  of  the  group.  The  test  is  covered  by  ciliated  ecto- 
derm, below  which  is  a  plexus  of  nerve-fibres  and  ganglion- 
cells  which  coordinate  the  movements  of  the  spines,  to  whose 
bases  muscle-fibres  are  attached. 

The  test  presents  certain  variations  iu  the  different  forms, 
but  there  are  also  certain  features  which  are  to  be  considereil 
typical  for  the  group.  The  apical  system  of  plates  is  Usually 
well  developed.  A  centrodorsal  is  present  in  the  genus  Ak- 
lenia,  but  in  all  other  recent  forms  it  is  replaced  by  a  series  of 
small  plates  which  constitute  the  periprod  in  the  simpler 
forms,  since  in  these  they  surround  the  anus.  These  plates 
are  surrounded  by  a  circle  of  five  basals  (Fig  262,  g),  usually 
termed  genitals  on  account  of  the  reproductive  ducts  opening 
by  a  pore  upon  them.  The  five  radials  (o)  are  also  repre- 
sented.  alternating  with  the  basals ;  and  since  the  teniiiual 
tentacle  of  the  radial  hydroctul-canals  protrudes  through  a 
pore  Hituated  upon  them,  and  more  eH[)«cial]y  since  a  ])igiiieiit- 
spot,  supposed  to  be  an  eye,  lies  frequently  at  the  base  of 


TYPE  EOmmDBBMA.  571 

tl.i8  tentacle,  these  plates  are  usually  knowu  in  this  firoun 
as  the  oculars.  Startmf;  fr„,„  each  ocular  and  each  Imt'l 
...ws  of  plates  pass  outwards  aud  downwards  towards  f 
...outh  the  test  being  formed  of  twenty  such  rows  Ix  end  L- 
m  mendlonal  hues  from  the  aboral  to  [he  viciniry  of  t  le  l^al 
pole  The  rows  are  ..-ouped  together  in  pairs,  five  of  the  pa  ri 
slart.ngfrom  the  genital  plates  and  the  other  five  from  t' 

.  e  perfoiated  for  the  enussion  of  tnbe.feel,  they  are  generally 
1-own  as  the  ambulacra!  plates  (Fig.  262.  ^),  'whilelhose "^ 


iuce  0/  anus, 


P.O.  263.-FiGcnE  showtno  thk  Ark.„ek,  ok  the  Apical  Svstem  o. 

-a.  —  ambulacrul  iirous.  /_,•., 

(in  =  anus  ~"  •"'«''""'" 'Julacial  areas. 

«to»  that  su,.h  t  s  ;re  f  ™e  ";''■""««■"«■"  -''''-■1'  "'Ji" 
smaller  ones  •  ,  ''p' .•'". '"■'"<"■  h.V  a  fusion  of  several 
_^^  ^^^^^ ->ne,      ch  of  w  h,oh  «  represented  by  one  of  the  pair. 

....ii^ir^LZ"''^::, '"'■•"V''''  "^ '"^  «■="""• '"-'- « 

l»"tiu  „ther.s  the  limits  of  fL  fnl        ,    "^'^^^^^  '-^^f^'-  -^^^  H 
iinutH  ot  the  tubercle  may  exteucl  so  an  to 


672 


INVERTEBRATE  MORPIIOLOOY. 


include  all  the  plates  of  tlie  apical  system,  and  at  the  same 
time  the  aual  opening  may  leave  its  position  near  the  centre 
of  the  apical  system  and  become  situated  in  the  interradius  A  /i, 
either  at  the  margin  of  the  flattened  disklike  test,  or  even  on 
its  oral  surface.  A  marked  bilaterality  of  form  is  thus  de- 
veloped, which  may  become  still  more  pronounced  by  a  mi- 
gration  of  the  mouth  away  from  the  centre  of  t^e  oral  surface 
along  the  line  of  the  radius  D,  which  at  the  same  time  be- 
comes more  or  less  altered  in  size  and  form,  and  consequently 
dissimilar  to  the  other  radii  (Fig.  263).     In  these  cases  it  is 

possible  to  recognize  in  addi- 
tion to  oral  and  aboral  surfaces 
anterior  and  posterior  poles 
and  a  right  and  left  side,  the 
median  line  of  the  body  pass- 
%  ing  in  front  through  the  radius 
'*  D  and  posteriorly  through  the 
interradius  AB.  Three  of  the 
radii,  C,  D,  and  E,  thus  lie  in 
the  anterior  half  of  the  body, 
and  for  descriptive  })urposes 
these  have  been  termed  the 
trivium,  while  the  two  posterior 
ones,  A  and  JJ,  constitute  the 
hivium. 

The  mouth,  which  is  usual- 
ly situated  in  the  centre  of  tlie 
aboral  surface,  is  surrounded  by 
an  area,  the  peristome,  which 
has  imbedded  in  it  only  a  few  scattered  calcareous  plates  and 
consequently  possesses  a  somewhat  leathery  consisteucj. 
An  oral  system  of  plates  cannot  be  distinguished  in  adult 
Echinoids. 


Fig.  363— a  PETALosTrcHous  Eciir- 
NOID,     Britisopm    lyrifera,    FiiOM 

THE   AlJOHAL   SUHPACK   WITH  THE 

Spines  hemoved  (after  a.  agassiz). 
D  =  modified  ainbulucnini. 
/  =  fusciole. 


The  marked  bilateral  symmetry  referred  to  above  aa  occurring  in  cer- 
tain Ecliiuoids  ia  undouhtciHy  a  secondary  condition,  those  forms  in  wiiii'h 
tlie  Miouth  is  central  and  tlio  anus  approximately  so,  and  wiiose  bilati'i'.iliiy 
is  indicated  only  by  tiie  madreporiforin  tubercle,  being,  there  is  cvi  ry 
reason  to  believe,  the  most  primitive.  The  l)ilaterality  cannot  be  regarded 
as  a  reversion  to  the  more  primitive  symmetry  of  the  hvrva,  since  in  the 


fc> 


TYPE  EVIIINODERMA. 


573 


uj  vv  nch  .t  is  „,ost  pronounced  are  the  most  Inghly  SIC  tiatek  t^^^^^^^ 

Projectiuf;  iuwarck  from  the  i.mer  surface  of  tbe  te»t  i,,' 
H.e  neighborhood  of  the  peristome  Me  frenuentlv  to  L  f        , 

^b.',  au),  which  may  either  be  coiifiue.l  to  the  inter-imb,,!  „     i' 
Pla  es  or  occur  also  ou  the  ambuh.crals,  unit  u  "il  it t  l! 

h lougli   w  „eh  ,,,„  radial  hydrocel-caiials  ami  nerve-  ords 
V^.     In  tlie  flattened  dislclihe  forms,  sncli  as  Echi,uZZus 
the  e  ,,1  hxrs  are  much  more  numerous,  extending  fr  m  the 

M  ace  of  the  test  are  nnmerons  spines,  each  of  which  is 
l".ll"wed  out  at  Its  base,  the  hollow  fitting  over  the  coi  ve.i  ' 
"1  a  tubercle  npou  the  test.  This  b-ill  •„,  1  „  i  ,  f  """"'y 
allows  of  a  fre'e  »n,veinent  of  tl^i^'irtv  dif:  ■''"'' 
...nement  which  is  effected  by  mns'ces  «L     ,g'";i: 

N  base      Tiir       "1;  "'"'"''  '""'  '"'■""■"«  "  «'-"'  a  i.,™^ 
s  base.     The  spines  thus  serve  as  eflicient  organs  of  locorao 
t .  n,  usurping  this  tuuction  entirely  iu  some  forms  w        Tn 
others  they  are  ahled  by  tli,i  tube-feet     Thev  1        ■ 
'...■",„  serve  as  defensive  ■:truct„rcs,  allt  ^^,^1^:^: 
a  e  l,mg  and  slender  and   readily  penetrate  th,      U   "f  less 
p.-otected   animals,  or  in  .«/,»„„.„„.„,  ;„  ,,,;„„  \  ^  j-^ 


674 


IN VEBTEBIi A TE  MORPHOLOQ  Y. 


spines  are  soinewliai;  eulargeil  towards  the  tip,  the  enlarge- 
ineut  contaiiiug  a  poison-gland  whose  secretion  is  injected 
into  the  wound  produced  by  the  spine.     Pedicellarise,  which 
have  already  been  noted  as  occurring  in  the  Asteroidea  and 
the  Euryalid  Ophiuroidea,  are  richly  developed  in  the  Echi- 
noids,  more  especially  in  the  neighborhood  of  the  mouth  aiul 
anus.     They  assume  varying  forms,  in  the  typical  one  (Fi<f. 
264)  being  composed  of  a  stalk  surmounted  by  three  calca- 
reous  pieces  or   teeth,   hinged    upon    the 
stalk,  and  capable  of  being  divaricated  and 
approximated  by  means  of  muscles.     Each 
tooth  bears    cushionlike    elevations   which 
are   tactile  in  function,   so   that   the   three 
teeth    are    vigorously   approximated    when 
touched   by  any   foreign    body.      In   some 
pedicell;iria3   the  teeth  are  very  much    re- 
duced  in    size,    but   in    their    place    three 
mucous   glands   are    developed,    structures 
sometimes  found  also  in    association  with 
well-developed  teeth.     The  functions  of  the 
pedicel! arise    may   be    various ;    they   may 
LAKiA  FiioM  Doro-    ggrve   for   the  prehension    of    prey   or  for 
fticc.S'""'"   VroteHiou,   and  tliey  have  also  beeu  «eeu 
m  =  muscle-tibres.     to  remove  excreta  from  the  surface  of  the 
test  in  the  neighborhood  of  the  anus.     lu 
the   bilateral  Echinoids  a  third  form  of  spine  is  found,  of 
small  size  and  covered  hj  a  richly-ciliated  epidermis.     These 
davidw,  as  they  are   termed,  are  usually  associated  together 
in  groups  of  considerable  extent  termed  Semites  ov  fasciokH, 
occurring  esjiecially  in  the  neighborhood  of  the  plates  j)er- 
forated  for  the  emission  of  tube-feet  (Fig.  208),  and  in  the 
vicinity    of  the   anus.     The    clavula?   have    a  rich  supply  of 
nerve-tibres,  and  are  on  this  account   supposed    to   be   sen- 
sory  in  function,  though  they  may  also  assist   in    renewing,' 
the  water  in  the    vicinity   of  the  tube-feet,  which    probably 
assist  to  a  greater  or  less  extent  in   respiration.      A   fourth 
variety  of  appendage  to  the    test   is   formed    by    the  sph<v. 
ridin,  which    consist    of    a    stalk    surmounted    bv    an    ovul 
mass  of  carbonate  of  lime  traversed  in  all  directions  by  deli- 


FiQ.  264.— Pedtcei,- 


an     oviil 


TYPE  ECHINODERMA.  575 

cate  canals      These  organs,  which  are  iisually  quite   small 
are  situated  in  the  vicinity  of  the  ambulacral  "pores  ox  nel^ 

:L::;:LTtL^^^  ^-^^^^^^  *^  ^-^  ^  --^>  p-C 

Owing  to  the  presence  of  the  firm  test  the  muscular  system 


\Ul  Hi' 

Fig.  265.— Diagram  showing  the 
Al  =  Aristotle's  lantern. 
<tmp  =  ampulla. 
an  =  aboral  nerve-riug. 
as  =  axial  siuus. 
au  =  auricula. 
ftr  ~  external  brancbia. 
Co  =  coelom. 

0  =  reproductive  organ. 
Od  =  genital  duct. 

Op  =  genital  pore. 
Or  =  genital  racbis. 
hr  =  hydrocoel-ring. 

1  =  (Bsopbagns. 
Ir  =  lacunar  ring. 
M  =  madreporite. 


Structure  of  an  Echinoid. 

nr  =  cpitbelial  nerve-ring. 

oc  =  ocular  plate. 

og  =  ovoid  gland. 

pa  =  perianal  space. 

PP  =  periproctal  space. 
pph  =  pel  ipbaryngeal  space. 

pv  =  Polian  vesicle. 

H  =  rectum. 

rh  =  radial  liydrocoel-vessel. 

rn  =  radial  nerve. 

sc  =  stone  canal. 

si  =  sipbon. 

sp  =  spine. 

tf=  tube-foot. 

t(  =  terminal  tentacle. 


is  but  feebly  developed,  being  represented  Iw  fi 

The  ca.lom  (-    265,  Co)  U  comparatively  spacious,  though 


576 


INVERTEBRATE  MORPHOLOGY. 


\ 


traversed  in  some  forms  by  the  calcareous  pillars  already 
meutioued,  as  well  as  by  a  perforated  meseutery  extending 
from  the  inner  surface  of  the  test  to  the  intestine  and  follow, 
ing  the  convolutions  of  the  latter.    In  the  bilateral  Echinoids, 
which  as  a  rule  swallow  large  quantities  of  sand,  the  mesen- 
tery is   much  stronger  than  iu  other  forms,  and  additional 
mesenterial  bands  are  added  to  assist  in  the  support  of  the 
intestine.     As  in  the  Ophiuroids,  a  circular  partition  extends 
from  the  oesophagus  outwards  to  be  inserted  into  the  test  iu 
the  neighborhood  of  the  auriculai,  enclosing  a  peripharyngeal 
space  (Fig.  265,  ppli),  which  has  no  communication  with  the 
rest  of  the  coelom,  and  contains  the  organs  of  mastication  when 
these  are  present.     In  many  forms  the  partition  is  poucIkhI 
out  into  five  radial  diverticula  Avhich  project  into  the  general 
coelom  and  are  known  as  the  organs  of  Stewart  or  as  internal 
branchiae.    In  those  radial  Echinoids  in  which  these  structures 
are  absent,  ten  lobed  diverticula  of  the  floor  of  the  peripharyn- 
geal space  project  upon  the  outside  of  the  body  at  the  margin 
of  the  peristome,  a  pair  being  -ituated  in  each  interambuJii- 
cral  region  ;  these  are  termed  external  branchise  {hr).     At  tlie 
aboral  surface  of  the  body  in  the  radial  forms  a  partition 
similar  to  that  enclosing  the  peripharyngeal  space  is  found, 
surrounding  tlie  terminal  portion  of  the  intestine  and  enclos- 
ing a  subperiproctal  cavity  {pp),  while  within  this  occurs  u 
second  partition  shutting  oft*  a  perianal  space  {pa).    Muscular 
fibres  occur  in  these  partitions,  and  it  has  been  suggested  that 
by  contracting  and  thus  compressing  the  fluid  contained  in 
the  spaces  they  serve  to  close  the  lumen  of  the  rectum  and 
the  anus. 

As  regards  the  axial  sinus  {as)  the  Echinoids  resemble  the 
Asteroids  and  Ophiuroids  in  that  the  portion  of  the  cadom 
into  which  the  larval  stone-canal  opens  persists  in  the  adult 
and  f(jrms  a  pouch  extending  downwards  towards  the  oral 
surface  parallel  to  the  stone-canal,  the  ovoid  gland  {og)  devel- 
oping iu  its  walls.  Into  the  upper  portion  of  it  the  adult 
stone-canal  {sc)  opens,  and  it  communicates  with  the  exterior 
through  the  madreporiform  tubercle  {M). 

The  so-called  blood-vessels  are,  as  in  the  Ophiuroidea, 
portions  of  the  lacunar   system,  and  are  contained  in  peri- 


TYPE  ECHINOBERMA.  577 

IZei  Tt-'  ^  "'"  '■".'""!  ^"'"-^iic  siunses  have  been 

s,»  of  fave  tabes  lying  between  the  radial  liyJiocoel-canl 
ana  the  radial  nerve-cc-ds,  and  terminating  Mindly  It  the  r 
ora  extremities  by  coming  into  contact  with  the  peripharyT 
«eal  partition  ;  they  are  not  continued  within  the  paSon  and 

«  eldir,:"''"""",''""  ""™-  '"•'^  '"™""-  «^^'-  --  i"teof 
hve  ladial  lacume,  lying  ,n  the  perih,emal  canals,  penetratin.. 

mto  the  peripharyngeal  space,  where  they  nnite  i,  to  a  c 3 

..rcumoral  lacuna  (Ir),  from  which  branches  pass  to  tl  e  ™ils 

"f  the  digestive  tract  and  which   is  i„  connection  witi        ! 

ZZ    \  ,  •      '''  '""■'■  ^"'^'  ""  ■"  <"''"•  fo™«.  stands  in 

Jose  relationship  to  the  reproductive  organs,  its  la^un^  bein" 
continued  into  the  walls  of  the  genital  cords. 

Ihe  hydrocoel  has  the  usual  arrangement  of  a  perioeso- 

ocular  phie      1"'"""^ "'S  "'   "  *-tacle  («)  perforating!  „n 
(«  o  Let  !i        n  ".        )"="'»'"'P'">g«"l  ".'S  the  stone-ctnal 
W  passes  aborally  to  open  into  the  axial  sinus  close  to  the 
^adreporiform  tubercle,  and  in  addition  in  the  lad  al  Ectf 
noids  the  ring  has  attaehe,l  to  it  in  each  interradius  a    pongy 
rncture   which   is    usually   termed   a   Polian   vesicle  Zf 
ongh  t  ^se  structures  in  other  groups  are  saclike      The 
abe-feet  (y)  which  perforate  the  ambulacral  plates  are  in  tl» 
uajori(,y  of  forms,  and  especially  in  the  radial  ones    v  ry 
eUensible  and  provided  at  the  tip  with  a  sucking-disk,  and    o 
assist    he  spines  in  locomotion.     Two  pores  as  a  me  exist 
or  each  oot ;  through  one  of  these  the  branch  issuing  ZL 

0..ck  tiom  the  foot  mto  the  interior  of  the  body  to  terminate 
m  a  saclike  ampulla.  The  feet,  however,  near  the  a  K,r  1 
.urlaoe  are  frequently  branched  and  lack  a  sucker,  .^eivbg  a 

c  piratory  function    rather    than  a  locomotor,  and  in  the 

only  on  the  aboral  surface  of  the  test,  nearlv  all  the  feet  may 

assume  a  tentacle  like  or  pinnate  form  and  become  respirator/ 

The  digestive  tract  in  all  those  forms  in  which  the  mouih 

-cupies  the  centre  of  the  oral  surface  is  provided  with  a 


578 


INVERTEBRATE  MORPHOLOGY. 


li  '4 


pharynx  surrouucled  by  a  complicated  calcareous  masticatory 
apparatus  usually  termed  Aristotle's  lantern  (Fig.  265,  Al,  aiul 
Fig.  266).  Wlieii  most  highly  developed  it  has  the  form  of  a 
pentagoual  pyramid,  whose  apex  is  directed  towards  the 
mouth  aud  consists  of  five  similar  portions  united  together. 
Each  portion  contains  an  elongated  ribbonlike  tooth  (Fi(^. 
266,  t)  lying  in  an  interradius  and  projecting  slightly  beyond 
the  lips  of  the  nouth,  though  for  the  greater  portion  of  its 

length  imbedded  in  ;i  calcareous 
socket  or  alveolus  (a)  composed  of 
a  right  and  a  left  h;i]f  united  above 
by  epiphyses  (e).  Between  each 
pair  of  alveoli,  at  their  basal  ends 
is  another  calcareous  piece  termed 
a  radius,  and  below  each  of  these, 
i.e.  on  its  oral  surfaces,  lies  another 
piece,  the  radula  (r).  Muscles  pass 
to  this  complicated  apparatus  from 
the  auriculse  and  from  one  piece  to 
the  other,  producing  approximation 
and  divarication  of  the  projecting 
tips  of  ihe  teeth.  The  presence 
of  this  apparatus  brings  it  about 
that  the  circumoral  hydrocoel  and 
lacunar  rings  are  forced  back  some  distance  from  the  moutli, 
surrounding  the  oesophagus  just  where  it  leaves  the  lauteru. 
It  seems  well  accordingly  to  speak  of  these  rings  as  beiug 
pericesophageal  rather  than  circumoral. 

On  leaving  the  lantern  the  dieostive  tract,  starting  in  the 
interradius  1)E,  passes  around  th''  coelomic  .'avity  in  the  direc- 
tion of  the  hands  of  a  AvaLcL,  until  it  reaches  the  interradius 
CD,  when  it  bends  abruptly  on  itself  and,  on  another  pluue, 
nearer  the  aboral  surface,  retraces  its  course  almost  to  its 
point  of  starting,  whence  it  passes  to  the  anus.  The  portion 
of  the  intestine  immediately  succeeding  the  pharynx  is  termed 
the  oesophagus  aud  is  succeeded  by  a  slightly  wider  intestine, 
the  junction  of  the  two  parts  being  in  some  forms  furtlier 
indicated  by  the  occurrence  at  that  point  of  a  large  caecum. 
As  a  rule,  however,  appendages  to  the  digestive  tract  are  rare, 


Fia.  268.  — Aristotle's  Lan 
TERN  FKOM  Avbacia. 
a  =  nlveolus. 
e  =  epiphysis. 
r  =  nulula. 
t  =  tooth. 


ii  .if 


TYPE  BCamODEKMA. 


67» 

th.  oiily  one  occurriuB  with  any  ,„arked  ,lw-,.„e  „f  coiiHtam.v 
l.en,K  the  mphon  (Fig.  265,  «•),  a  tube  which  aiiseVf™'  !l ! 
-sophas„s  an<U.„n..  closely  applied  to  the  int  Le  to  ol 
>»«u  .uto  .t  at  the  extremity  of  ti,e  oral  coil.  Th  fuL  ion  J 
t  t  if  """"rro-".  to  be  respi..atory,  but  it  is  to  b  ^ 
that  It  13  wanting  m  all  the  members  of  one  of  the  or,le,-«^H 
ay^astroi<Ua),uio  which  the  group  may  be  iivl:,       "  <"" 

consi  t'i,>r ';   :     ""■""■^^^■»'«'»  '--^  'l'"  ---l  arrangen,ent 
consisting  of  a  perioesophagea    ring  (Fie    w.r,    ...i  .,f ,  „ 

radial  ooras  M.    As  m  the^phiui-ijl^l^.t;     t  e  '2™ 

ith  ,  H  r  '  '"™  "'^"-'''^«»  *■'■"»  ««  ectoderm  and  s uuk 
«lthi.  the  body-eavity,  and  accordingly  there  is  to  l,e  fn  ,^  1 
an  epineural  sinus  lying  below  the  i"ve-c  X.  Be  ol  he 
nerve-ring,  however,  no  sinus  is  to  be  found    ■  nd  ./ 

cttr":^"  r  T"  ;r  i"'  '"^  ^^^^^^ :;:':: 

liie  extiemity  of  eacli  radial  cord  fuses  with  the  ectodenu  in 

SI  t:t^'  Tn  ^"  '^^  "^"^^^  ^^^*^'  -dt  t:;," 

uted   to   the    walls   of   the    terminal   tentacle.      A   muscular 

uerrous  system  is  present,  consisting  of  five  mM.t«  1 

the  aboral  surface  of  the  radial  njJJll       t  ^1    rtW 

s\  th^^r'^^-ti  ""''^r:^ ''-'''  -  ciiLct^rec^i^z 

utli  each  othei  ,  they  send  fibres  to   the  muscles  of  the  mas 

w^Wh^  pass  to  the  walls  of  the  ducts  It  the  T^tduX: 

Sense  organs  of  various  kinds  have  already  been  referred 
o,  such  as  the  terminal  tentacles  of  the  hydroacl  canals  he 
fascioles,  and  the  splneridia.  In  addition  to  thei  „t me 
spots  occurring  on  the  ocular  plates  have  be  n  r^VaS  as" 
eyes,  and  somewhat  complicated  structures  of  a  br  ght  blue 
color  which  occur  abundantly  over  the  surface  of  t  l.l 
a  .P~f  .>,We„.  have  also  been  regarded  l^eti;" 

--e-ul/"-!  l'"'  '7T-  ""  '^"•■°^'™'"''  -y^'em  consists  of  the 
ge-ital  «,rds  and  the  reproductive  organs.  The  former  hnve 
their  origin  from  a  single  cord,  which  is  a  hollow  t„be  ltd 


mo 


INVEHTEBRATE  MOHPHOLOQT. 


iuternally  by  immature  germ-cells  aud  i.s  connected  at  its  on,! 
extremity  with  the  ovoid  gland.  It  passes  thence  to  Uie 
aboral  surface  of  the  body,  where  it  forms  a  ring  (Fig.  26G,  r/n 
from  which  in  each  intorradius  a  branch  passe:-;  outwards  to 
expand  into  a  highly  raconiose  sac,  the  reproductive  org.ui 
{G).  In  some  forms  the  number  r,f  the  organs  may  be^v. 
duced  to  lour  or  even  to  two,  though  live  is  to  be  regarded  ;is 
the  ypical  number.  Each  organ  oi)ens  to  the  exterior  by  ;i 
special  duct  {Gd),  usually  opening  on  a  genital  plate,  but 
sojuetimes  in  au  int^ -radius  outside  the  genital  plates. 

As  already  noted,  there  is  considerable  variety  in  the  rela- 
tive positions  occui)ied  by  the  mouth  and  anus,  and  many 
diiierences  of  structure  are  associated  with  these  variations. 
It  IS  possible,  in  fact,  to  divide  the  Echinoidea  into  tlir, ,. 
orders,  which  are  marked  out  by  the  positions  of  the  opeuin-.s 
of  the  digestive  tract.  " 


1.  Order  Desmosticha. 

In  these  forms  the  mouth  occupies  the  centre  of  the  oval 
surface,  and  the  anus  approximately  that  of  the  aboral  sur- 
face, the  radial  symmetry  usual  among  Echinoderms  beini; 
well  marked.  The  body  is  usually  more  or  less  spherical  in 
form,  though  occasionally  soraew)iat  flattened  ;  all  the  anihu- 
hicral  ])lates  are  perforated  hn-  the  emission  of  tube-feot,  and 
all  live  ambulacra!  areas  aie  equally  deveh)ped  (Fig.  202).  In 
the  members  of  this  order,  conseijuently,  the  bilateralitv  is 
marked  externally  only  by  the  position  of  the  madreporifi.nn 
tubercle. 

The  prinniry  ambulacral  |)lates  frequent] v  fuse  to  form 
secondary  plates  each  of  whicli  i.s  i)crfoiated  by  several  ])air,s 
of  pores,  as  nniny  as  six  occurring  on  some  phites  i.,  AV/v^m/y. 
locenfrnfits.  The  spines  are  sometimes  exceedingly  long.'/is 
in  Diiuhnw,  and  are  usually  well  developc^d.  being  hi  Arh„'m 
equal  in  length  to  about  half  the  diameter  of  the  bod  v.  The 
auricuhn  are  the  only  representatives  of  the  calcareous  i)lafos 
or  bars  which  extend  from  the  oral  to  the  aboral  surface,  and 
au  Aristotle's  hmtern  is  always  w(>ll  developed,  its  ahv..|i 
being  much  longer  than  broud.   In  this  order  external  brauchio) 


TYPE  ECIIimDEUMA. 


-0%  tl.erefore,  to  clivide  the  orT  !  "'^^'"'-  ^*  ^«  «»«t<>m- 
ENTO.K.XCHU..,  i,,,  „'^.:C^,:;^'^  ^-  sul,.,.oups:  the 
ATA,  iuclnding  all  other  fon  s  fudT      V^'^  "^'  J^ctobiunchi. 


2.   Order  Clypeastroidea. 


•■".'"»  ■■«  situate,!  iu  t!  .  in  e'  !Z   :«      .T '"■"'  l"""'  '"""«' 

"f  tlie  flattened  test  •,  ■  i,    A' ;  ',    '  """""  "'  "«  ■"".■.-(« 

'"•"   siuface,  as  iu   JM,V,,       i,,  '•    **•  ''"'>'  "'■  "u  Us 

«4.7«a*.tl,eb„.lyis|,„t»ii,,|,t, 

('■•'tteued,   but  iu    ti.e   t,v„  otl,er 

Jjeuem    nh-eadv    n,eu,i„„ecl     the 

fl.-.tteu,ug  is  eaiTied  to   such   „„ 

"■^'7"  tl,,.t   the  test  has  „  ,uo.e 

"      ess    .hsklike  shape,   wl.euce 

"";'"""  ^'"'''-'"""•"•s  a,,,,lie,l  to 
'•ortniu  foruis. 

1.1  aocordauce  witi,  '.he  shift.         -^.-       'V-Pf^Si^ 
7  "f  '1-  «..»»  fa.u,  the  centre         ^\*^^^*^ 

l,,,'"     "l^;""'     ».v»te".     cert,.iu'":-"--'*'".vp..:.v»r „,:,„,. 

'l''-"Ke.s    take    plaoe    i„    it,   t,.e    .Z  f"'"""'""""".    ,».,„", 
■;p    ma,ke,I  heiu«  au  e.teusio,      «;:.,.  r.,,t,;r',;;„  «---^ 

i--  -.oiu«  We?":  sr  ortr;' '"■  "'""■^- "-  --■" 

:""'-l-eral  plates,  au.,  iu  si™,'"'"  ""  ""f  ,"'  "-  i"te,- 
"""■■•■'"lius  .//,au,i  the  eonesn  ,<  ,  I'"™,""'"'  l««t«i.,r 
» ■'"«"«  (/:W»-„,„w/,„,-,„)     The  '  .'■"'"■'"'"'■'"•"  "W".  is 

"'■"  "»  "  .-"h,  eouHue,!   to  the  .il'"      '."'"'"''"'•'■"'  I'l'""" 
»'"f-e,thep,a,e,ueaMho    1  '■''''■''""   "'  ""'   »I'"™I 

"'"   "■•">  ™rfa..e   heiu,  tp.^^^   L"'  ","  "'»'  ",■"'  "-"  " ■ 

«i"  of  course  v,„.y  uar,;>v  a    ,  ;.„,  l";"  ••!':"'"««'  i''"l-H 


f(''H(Iiially  onj.t! 

«'viug  thus  the  appear 


o'"    fi'^    tiu3 


»UNM 

•aiice 


npical  end  <,f  th 


;7PH«MtowardHtheod^eof  th. 
'I  live  liower-petals,  aud  h 


e  oerioH,  -mhI 

!i(^  tesf, 

oiice 


682 


INVERTEBRATE  MORPHOLOGY. 


the  ambulacra  or  areas  occupied  by  perforated  plates  are 
termed  petaloid.  lu  Echinanichnius,  for  instance,  the  })lutes 
after  having  reached  their  greatest  widtli  retain  it  to  tlieir 
abrupt  termination  (Fig.  267),  the  petals  being  then  termed 
open,  but  in  other  forms,  e.g.  Jlellita,  they  contract  again 
l)eripherall3',  in  which  case  the  ambulacra  are  said  to  bu 
closed. 

The  pores  belonging  to  each  pair  are  generally  united  by 
a  groove,  and  are  termed  yoked  pores,  and  iu  Mellita,  for 
example,  in  addition  to  the  pair  of  yoked  pores  on  each  ])lato 
there  is  a  third  one  situated  near  the  middle  line  of  the  am- 
bulacrum. The  tube-feet  which  project  from  the  yoked  jujres 
are  frequently  pinnate  in  form,  while  those  emitted  through 
the  single  pores  are  simple  and  tentaclelike.  The  spines  are 
generall}'  very  small,  though  those  of  the  oral  surface  serve 
for  locomotion. 

In  Mellita,  towards  the  periphery  of  the  test,  the  imper- 
forate ambulacral  plates  of  the  radii  A,  B,  6',  and  E ([.o  not 
meet,  leaving  elongated  holes  passing  through  the  test,  and 
the  same  thing  also  occurs  with  the  plates  in  the  interradius 
AU,  so  that  altogether  live  such  holes  exist.  In  other  forms, 
instead  of  holes,  notches  occur  at  the  margin  of  the  test,  ami 
other  interambulacra  than  that  in  which  the  hole  occurs  in 
MelUUt  nniy  be  atlected.  Calcareous  columns  extend  from  the 
oral  to  the  aboral  surfaces  of  the  test,  being  especially  almn- 
dant  towards  the  peri|)hery,  and  calcareous  plates  uniting  the 
two  surfaces  occur  on  either  side  of  each  and)ulacrum.  Au 
Aristotle's  l.mtein  is  present,  but  the  alveoli  are  usually 
broader  than  long. 


3.  Order  Pettlosticha. 

In  this  order,  as  its  name  indicates,  the  ambulacra  are 
usually  petaloid,  ami  the  bilaterality  indicated  in  the  Cl\  |i(  as- 
troids  is  more  pronounced,  since  neither  the  mouth  nor  tin' 
anus  r<itains  its  original  position  at  the  centre  of  the  oral  orj 
a}>ical  surface.  The  anus  lies  in  the  posterior  inttuiailins 
yl />,  while  the  mouth  has  moved  forwards  to  a  greater  oilissl 
extent  along  the  radius  D.     The  test  is  oval  or,  freijui  iillv, 


TTPn  BcmmmHMA.  533 

somewhat  heai-e-shaped,  owintr  tn  fl,„      .    • 

■"o>-e  or  Jess  depressed    ol   to  ,,.™  '  ""^^'  ^  ^^^ 

The  madreporiform  tnl»,  ?  ?  "  *'™°™  (^W  263). 
-"'.e  of  the  ap  ea  Vstrttr  r''  "^""^  '"'-«''  «^« 
""■«  'iividf,.K  the'apiea?:^;;,,  "'"*''  'T"°'  i-i<^^r.ai.., 
«  obliterated  in  ail  members  of  .,^''%P"^'''™>-  gemtal  pore 
live  glaad  ™.respo„di2  to  .t  dt/  '  """' **">  '■«P'<'^uc- 
>«pi-oductive  orRans  aid  ,1     <'"'''PI""'r3.  so  that  but  four 

-«e  forms,  ho^te  ,  «  e  redToLT  ,T'"'  <*'"'"''-)•  I" 
»'"'.  pores  is  carried  tilf  furth  7v  t  '!'^';''P^°d»"«ve  organs 
|i«ht  anterior  iuterradius^XftlT'  TT"™"^ '"  "'« 
...terradins  Z^^' may  also  disan^r  /"'^  "  '""  ■""«"<»■ 

■"«  pan  of  the  n>ad^eporif'  .^rbtrersoTh'r'/'''^  ''^^°"'- 
■■.■productive  organs  and  <renit,l  "'  "'"  ■"■"'I'er  of 

foira).  The  ambuh  ra'are  uXdT""  'f  "''""''"  '"  '« 
Leart-shaped  forms,  in  which  he  ,f,  f  """'"■• ''^I"^'''''"^' m 
C".«es  much  modified.    Fasciol,  '"  "'"'"•'''<"•«•"  be- 

f-«e,l  in  diirerent  manners  indir  .*'"""""^  P"-"^™'.  - 
-umling  the  a„,b„lacra  I  others?  '''"'''="•  '"  ^°""    ™'- 

;■'  'I'e  anus,  and  in  otirerrarr"  17'"'"*' """«'"  "'^  "'^'--'''y 

'-»•  Spioes  are  .C:Zy'Xj:t  ZT""'  ■»'"'"''  » 
moderate  length      Th«  ,n^  /.    P^eseut  aud  are  u.sually  ot  a 

;--tea  lip  o?  /abrn^  ^od  ^d  b"".",'"^  '^^""'^  ^^  ^^^  ^ 
'^^"low  the  "-atl.openinJofte  If  .  :f  *'""""  ^^^^-'^^ 
a.ul>nlacru,u  All  There  is  L^  a  w''^"^"  Posterior  inter- 
l^etalosticha.  '"  "°  Aristotle's   lantern   in   the 

l>eoelotment  of  the  Echimidea  -Th„    »      ,  ' 

"•""••OS  very  .si,„ii,„.  t„  that  of    ho  rw      '.'?^"'"n'^^"t  is  i„  if.,  general 

Ml.  prroneoU  j;:.:;:^^^^  eases  be  .is:;:  „  J:! 

""  I  <>.st.M-i,„.  ,,orti„„  „f  eho  body  whip  .  .         ^"^'"'''''".'/'^v)  processes  „no„ 

«"'  ''"•"  occur  „,,ou  th,  ,i,,,.,  ,,;        '/        ■   ^'^  t«-ooarliko  lolu-.s  fri,,,^., 

-    "own  as  Ciliated  epauiett:.";:    ^  T'^  ''"^'r"  "^  ^"«  '>""    - 
PoM.Tior  portion  of  fl,,,  body  of  the     ..r"^  •'""■"'""  '^^'^'^^  i  >  the 

'"  ;-olH.ion.s,nps  of  the  vario,     ,'     ,  ^v'  '7'« '<''-'-"'".V  'Vsorbed. 
I  *'i''  ':eod  not  b(,  ji^Hiii  -li •  ■       *»"*"!'«  "Jive  already  l.e"..  -'  -     ■      , 


T     i 


684 


INVERT EBlt A TE  MOliPUOLOG  Y. 


primitive,  while  the  Clypeastroidea  and  Petalosticha  are  secondarilydo- 
rivi'd  forms.  The  bihitcrality  of  these  latter  forms  is  not  to  be  regarded, 
therefore,  as  having  any  phylogenetic  significance. 

Class  V.  Holothuroidea. 

The  Holothurians  (Fig.  268)  are  characterized  so  far  as 
tlieir  form  is  concerned  by  being  elongated  in  the  oral-aboral 
axis,  having  thus  a  somewhat  wormlike  form,  the  mouth  be- 
ing at  or  near  one  extremity  and  the  anus  at  the  otlier,  exee])t 
in  the  genus  lihopalodina,  in  which  the  two  oj)enings  are  ap- 
proximated.    As  a  rule  the  l)ody  is  cylindrical,  but  in  some 

forms,  such  as  Psohm  and  the  /iUmpodd, 
there  is  a  well-marked  flattened  ventral 
surface.  Three  of  the  radial  hydroco'l- 
canals  lie  upon  this  ventral  surface,  the 
other  two  being  dorsal,  and  it  is  usual  to 
a])ply  the  term  trivium  to  the  ventral  radii 
and  bivium  to  the  dorsal.  It  must  l)e 
recognized,  however,  that  this  use  of  the 
terms  does  not  imply  a  homology  with 
the  radii  similarly  named  in  the  Ecliin- 
oidea,  since  in  the  latter  the  radii  (',  1), 
and  A'  constitute  the  trivium,  whereas  iu 
the  Holothurians  it  is  the  radii  J,  U, 
and  K 

The  mouth  is  surrounded  by  a  circle 
of  tentacles  varying  in  number  from  ten 
to  thirty.     There  are  at  first  five  primary 

(Zoflrt.  A  IloLoTHiiuiAN.  t''"t''^^*l^'^'  iJiterradial  in   position,   wliioh 

are  formed  in  connection  with  five  ca'cal 
outgrowths  of  the  h3'droco>l-ring,  and  the  tentacles  subso- 
t^uently  formed  receive  branches  from  the  five  primary  ca'ca. 
In  shape  the  tentacles  vary  considerably,  being  cylindiii'iil 
iu  some  forms,  arl)orescent  or  pinnate  in  others  (Fig.  'iCKSi, 
and  in  others  peltate,  and  iu  some  forms  they  are  retractile. 

The  exterior  of  the  bod}-  is  usuall}'  covered  by  an  epithe- 
lium over  which  a  cuticle  may  be  developed,  but  iu  some 
forms  the  ectodermal  cells  siid;  into  and  become  fused  with 
the  subjacent  connective  tissue.     The  calcareous  skeleton  if* 


Fro.  2QS.—Pentacta  fron 


585 


TYPE  ECIIINODEllMA 
1    ,    »     ,  ,  ■  woo 

skeleton  is  represented  by  llJZZ'  TTZ'  ""  "'"— - 
I'orforated,  tuobbed,  so„Jti  "  ,  If  t  "/  ™""-  ^'-1-S 
".■  associated  with  au  auchorii  e  ^''*"^. "'  '"  <^'''"-odo,a, 

a.e  uot  suffieieutly  r,.„„ro„  '  'r^  spicules  iu  Synaptu,  aud 
"»"t,  which  i«  6V„„w"  Z  *^  ^  ■  "«"'"^  '°  "«'  i-tef-u- 
Tl-e  isBoi-KlicatlrofarCr.  ':  '"'"  '""•  *--'--*. 
WfenV.  a  circle  of  fi™  phte  ^'    "^  "^  "'*'*'  """-fi''  '" 

0-1  syste,,,  is  represented  t  T"""^'  "'"  """•  >""  "'« 
Piates  which  may  be  cWd  1  '',""■'""'  "''  ^'~'"«  ^y  five 
I"  other  parts  of  the  hlZl'tt'T''  """  '-'-'-• 
■"•■'tter  is  also  frequently  iL  u"  ,  ""*'.«r<^'"  calcareous 
'ive  tissue  of  the  wall  of  ft      ^1"'*?' •''■ '"  "'"  ""'"'-<'- 

«-lial  ossicles,  gro  ,ved  o     .W     TT'"''  '^'^''"""y  •><  «ve 

:-n.ydroca.l.catal»;rud  yCi!:      r  ,""  '""'"'  """"^ 
"'«  with  them,  thouJh  iu  tlK„!7  """"•"''f '  "■''««1«»  alternat. 

'^..t-.es  is  greater'th,:     Ttl    ™rb:r''f  h'"  """"•-  <" 
«s»icles  may  be  increased      X,       ^  ^  "'"  ""^'ra-Iial 

"-seutery,  au,l  i„  son  efn,,^  Its'"  "''  t"  '""■"'  "'  «'« 
•bvelops  in   the   wall   TZ   T      '  '^  T    "'"'''' "''^''"'^ 
I'Wseut,  though  the  plates  of  ^7        •""'■.     ''"""'  ""   '•■"■e'y 
otlier  forms  bear  tlim  td  ,f    "'r"'""'  ^"'"'''"'  ™'>  "  '«* 
The  ca,l„n,  is  trav  ;  ed  b^  eT    ,"'"  "'"  ''""'"'^  "'-«"«■ 
'lisostive  tract  to  th  ".>   'ti  M        •""r"'"'*-  uniting  tl!; 
-ailed  dorsal  niesen:^-'^^  ";,;";:    7.»'-'.  ^-ing  the 
■"'  ■no.-  portion  of  the  ini  radius  (V^tI'"''  'T  '"  "'« 
«'l<>m  which  surrounds  the  o-o,   , ,        •  '"""""  "*'  "'^ 

'«t,  as  in  the  Echinoid  1  „,;''«'"  ''<  »"';"■"'-•  '■-"  the 
'"•'  -.ilariy  i"  son,e  forms         Zt  'J^l^'r^"^-'^'  »P"ce, 
hpaco  surrounds  the  lern.i,  al  ,      ,  ''"'""""■'")"  Perianal 

'■'  ^map>a  and  its  alii  "  ,      '  IZ    T  f  ,",'"  '"«''-''"™  "«'. 


586 


INVERTEBRATE  MORPHOLOGY. 


\ 


of  the  Crinoids  iu  maintaiuiug  a  circulation  of  the  coelomic 

fluid. 

So  far  as  is  known,  the  portion  of  the  coelom  which  in  the 
embryo  opens  to  the  exterior  by  the  water-pore  and  with  which 
the  stone-canal  communicates  in  the  Asteroids  and  Echiuoids 
does  not  persist  iu  the  adult  Holothurian,  and  consequeutly 
there  is  no  axial  sinus,  and  it  is  doubtful  if  a  structure  com- 
parable to  the  ovoid  gland  of  other  forms  exists.  Schizoca-lic 
sinuses  corresponding  to  the  perihaeraal  canals  of  the  Echiuoids 
occur  in  their  usual  position  betweeD  the  nervous  system  find 
the  hydrocffil-canals,  and  consist  of  a  ring  accompanying  the 
nerve-ring  and  five  radial  canals  which  abut  against  the  ring 
at  their  oral  ends  but  seem  to  be  completely  separated  from 
it  by  septa.  A  lacunar  system  is  well  developed,  consisting 
of  a  plexus  in  the  walls  of  the  intestine,  the  various  branches 
uniting  to  form  a  dorsal  and  a  ventral  intestinal  vessel,  which, 
passing  forwards,  unite  with  a  lacunar  ring  surrounding  the 
oesophagus  at  about  the  level  of  the  hydrocoel-riug.  From 
this  ring  five  radial  lacunte  extend  backwards,  lying  in  the 
connective  tissue  between  the  radial  perihsemal  sinus  and  tlie 
hydrocoel-canala,  and  giving  branches  to  the  tentacles  and  the 
tube-feet.  A  lacuna  also  extends  from  the  pericesophu^^Md 
lacunar  ring  to  the  reproductive  organs  arising  from  a  thick- 
ened portion  of  the  ring,  and  this  thickening  has  been  re- 
garded as  the  rudiment  of  the  ovoid  gland. 

The  hydroccel  has  the  usual  arrangement,  consisting  of  a 
ring  (Fig.  261),  o)  surrounding  the  oesophagus  behind  tho  ring 
of  peripharyngeal  ossicles,  and  having  arising  from  it  a  stone- 
canal  which  in  tho  majority  of  forms  hangs  freely  in  the 
coelomic  cavity,  where  it  terminates  iu  a  madreporiforni  ]tlate. 
Iu  the  embryo  it  as  usual  opens  upon  the  surface  of  the  body, 
and  this  condition  is  retained  in  many  Ehisipoda,  in  wliich  tho 
canal  opens  upon  the  dorsal  surface  of  the  body,  probuhly 
indirectly  through  the  intervention  of  an  ampulla,  as  in  other 
forms.  In  the  majority  of  forms,  however,  the  connection  with 
the  exterior  becomes  lost,  the  ampulhi  which  is  present  in  the 
embryo  disappearing,  and  occasionally  a  number  of  secoii<hiiy 
1.   1 1.---       A  cJ.w,!,.  Voli'i"  vo^ud** ''''^  is  iiMiiallv  attaclii'i 

canals  llUVCivJp.        --i.  ami^iT:     t!.!i.;.. I-     -.-.i"   

to  tlie  ring,  but  in  some  cases  the  number  of  these  structure 


TYPE  ECnmODERMA. 


,  687 

maj  be  considerably  increase.!      P;      •  x 

from  the  ring  and  pL  Wa^  to  t^f  Tf"'  ^^^^^«  --- 

tliese  structures  are  more  th  n  V  *^"tacles,  branching  if 

^^ma,  airodota)  ^^l^^'  ^"^^  ^-^  forms  (//ol- 

ampulla.     Five  radial  canal  1     '""'\'  "'"  P^^^^^^^  ^ith 

nng  in  all  forms  except   leLt^.^  ''^^^™^^«  ^-m  the 

-^dial  hydrocoBl-canals  of  o^heT  F^^^^^^^^  corresponding  to  the 

tube-feet.  °*^^'    Echinoderms  and    bearing 

The  distribution  of  these  Jaffa.    ^      . 
-n,  forms.    lu  MoliSrJ^,:'llfT\^^  P-»«ar  in 

dor^l  canals  of  P^l„  ^H™  !^  ''^o^  "<>  '*»  f^om  the 

tnviumoftheEladpoda;  wLu  Z."  !  T''""'  ""■"  "'  "'« 
"l™g  the  lines  of  tlTe  ra.  iaTotn  ?  ''"^  ""^  ''«  "^''ged 
208)  or  naay  be  .eat  er:  1  ^Xit  ""T*"'  ''''^'^'  ^'«- 
body  (Tk,one).  In  form  tW  a —'"■  "'^r'''"'«  "'  "'« 
e.tljer  simple  fingerlike  processes  o7  T'"!^''"''''^'  "'^'"g 
sucker.     Frequeutly  the  tnbe  Iff  '^   ''I'P'"^    ^""'   a 

".e  Elasipodl  the/talTe  tfe  form  "oTsr'  '"^'^f'-  """  '" 
corneal  processes  arranged  in  pairs  ^^  «-ell-developod 

Owing  to  the  absence  of  a  firm  lest  in  n     tr  , 
tl.ere  is  a  much  more  extensive  del  !  '  ^"'"""•rians 

8.vstom  than  in  other  Echlnodermr  tI'™""  "'  "'"  '""^^'a^ 
body-wall  is  formed  by  a  layer  rfci  J  l"  """"■  ""*■'"'  »'  "'« 
0"  each  side  of  each  radi,tf  Wdro  "  "'  "'•"•'"'"'""•«^'  ""d 
muscle-bnndlo  (Fig.  269,  „)  rom  L.t^  "  ''  "  '""si'-'taal 
'»'"<"««  pass  to  the  p;r1p  „;"!elf  "'-T'  '""'""  "l'""'*' 
■■ee^ctors  of  the  tentacles  aSh-dir"'^^  """  ^""^  ^ 

As  staled  the  mouth  is  usualN     f 
'""'y  at  the  centre  of  a  dk™  .•,;,";",  ™'™'"'-  '^'"'  »'  "- 
'"  tl.e  Elasipoda  it  has  a  so  ,"«        1  f    "  '""'"'o^'  '™' 
•gestive  tract  is  a  simple  tube  '"hi    ,  '      ""■'*"''""-     T''« 

'"•tlj  straight  course  fr  ,„,  mZhl  "'T"'"'"^  '"'«  a  per- 
"  '»bent  twice  „p„„  it.  1  ",:;";': ''""""■■«  fequeitly 
-"Ji"K  limb  (Pig.  2fi9,/>,'.„  a  t  tr^^^  ""  «"'-ior  de. 
'lexeendmg  one  (/,).  The  term!,,  J  n*'  ^''}' ,""''  "  Posterior 
,  --"■■«  li."b  is  dilated,  t  i  ;  /  *^^  ?  f"  P"^'"''"'  •'«- 
.l»H,cle-bands(^)rad,^aet,.tl,.!r.,';^'?"''l')f™'«  whose  wall 

'Hiythmically  contractile,  and  lar^ltrtj^^^^^^^^ 


588 


INVERTEBRATE  MORPHOLOGT. 


the  SynaptidsB  two  much-branched  structures  termed  the  re- 
spiratory trees  {k).  As  their  name  indicates,  these  structures 
are  supposed  to  have  a  respiratory  function,  but  it  is  possi- 
ble that  they  may  also  aid  in  excretion,  the  waste  products 
of  metabolism  collecting  in  the  cells  lining  the  interior  of  the 


Fig. 


269.— Diagram  representing  the  Internal  A«Ai'oAi; 

THUKIAN  (after  Ludwiq  from  Leunis). 


^'^0- 


i'  =  cloucal  opening. 
k  —  respiratory  trees. 
I  =  Cuvierian  organ. 
m  =  dorsal  mesentery. 
n  =  duct  of  reproductive  orgau. 
0  —  reproductive  organ. 
p  —  lougitudinal  muscles. 


a  =  tentacles. 

b  =  calcareous  pharyngeal  ring. 
c  =  hydrocoelring. 
d  =  stoiie-cauals. 
e  =  Polian  vesicle. 
/,  g,  h  —  intestine. 
i  =  cloaca. 

9  =  radiating  muscles  of  the  cloaca. 

tubular  branches  and  being  carried  to  the  exterior  In  ii- 
desquamation  of  the  cells.  In  addition  in  a  small  number  of 
forms  {Holothuria)  there  occur  upon  one  side  of  the  cloucii  a 
large  number  of  slender  tubes  (/),  which,  at  the  will  of  the 
animal,  can  be  evaginated  so  as  to  project  through  the  aiial 
opoiitjg.  These  constitutG  the  orgau  of  Cuvier,  the  fuiictiou 
of  which  is  not  as  yet  satisfactorily  explained. 


TTPB  BOHlSODEttUA.  589 

The  epidermal  nervoas  system  consists  of  a  perioesoni,, 
geal  nug  aud  five  radial  nerves  as  iu  other  forms  !udTu  addT 
tan  hve  ,nterradial  nerves  pass  from  the  ring  to   be  tent^l  ' 

extremities  passing  tUrongl,  the  tissues  of  ILIo,^:,-^,":^;;;:: 
».th  the  ectoderm.  In  accordance  with  this  arran  Jmen  tan 
epiueural  smus  accompanies  each  radial  nerve  thou^r„\!  \ 
^"m  the  pericesophageal  ring.     The  mnsculaV  ne^U      .^ 

.ervous  system  has  bee'n  dLoverot  in'Ihe  H^lt  ir^-' 

uthal  lieive  close  to  its  origin  from  the  rinrr      T?,  i      . 
..nteins  .  number  of  otolith!  and  I  t:t^^^X 

^^^.uch  greater,  amounting  to  ajuf t^CsuL"  r;:.  ^Tf 

The  8.ynaptids  and  Molpadids  are  hermaphrodite  bnt  nil 
other  Holothuriaus  are  bisexn-.l  Tl..  «*F"iou  te,  but  all 
(Firr  9fiq  ^\^         .    7     '^^^^*^^"'^^-     Awe  reproductive  ortraus 


590 


INVERTEBRATE  MORPHOLOGY. 


-  r. : 


(lifFerences  are  associated  with  the  absence  or  reduction  of  the  ovoid  ghmd 
and  of  an  aboral  nervous  system.  The  number  of  the  organs  is  very  much 
reduced,  and  no  genital  cords  have  as  yet  been  discovered.  It  is  interest- 
ing to  note,  however,  tlie  existence  of  a  genital  lacuna  mentioned  above, 
in  association  with  which  the  reproductive  organs  seem  to  develop,  and  it 
may  be,  as  stated,  that  the  lacunar  thickening  from  which  it  arises 'is  to  be 
regarded  as  representing  the  ovoid  gland,  which,  as  has  been  seen,  is 
intimately  connected  with  the  lacunar  system  in  other  forms.  It  seems 
probable  that  in  harmony  with  the  shortening  of  the  stone-canal  and  its 
separation  from  the  body-wall,  and  with  the  abortion  of  the  axial  entero- 
ccBl,  there  has  been  a  shortening  of  the  genital  cords  so  that  the  aboral 
ring  no  longer  exists,  and  the  reproductive  organs,  reduced  in  number, 
develop  directly  upon  the  wall  of  the  genital  lacuna.  It  must  be  remarked 
that  in  some  forms  there  is  no  distinct  genital  lacuna,  but  the  reproductive 
organs  are  associated  with  the  intestinal  lacunae,  a  condition  which  may 
be  secondary. 

Development  of  the  Holothuroidea.— The  typical  larva  of  the  Holotlm- 
rians  is  known  as  the  Auricularia  (Fig.  270),  and  is  distinguished  from 

that  of  the  Asteroids,  Ophiuroids,  and 
Echinoids  by  being  destitute  of  armliko 
processes.     In  later  stages  the  ciliated 
bands  fuse  in  such  a  manner  as  to  form 
St  a  series  of  circular  bands  surrounding 
the  barrel-shaped  larva  and  recalling  tlie 
<'P  larva  of  the  Crinoids.     By  the  gradual 
elongation  of  this  larva  and  the  disap- 
pearance of  the  ciliated  bands  the  adult 
form  is  acquired,  there  being  no  absorp- 
tion of  any  extensive  portion  of  the  larval 
body  as  in  the  Brachiolaria  and  Plntous. 
The  Phylogeny  of  me  Echinoderma. 
—The  Echinoderms  form  a  well-defined 

group  siiowing  little  indication  of  aflini- 

PiG.  270— Auricularia  Larva  OP  ties  with  other  forms,  and  the  establish- 


Synapta  (after  Semon). 
dp  =  ciorsal  pore. 
-fir  =  hydroccel. 
pt  =  primary  tentacles. 
at  =  secondary  tentacles. 


ment  of  a  plausible  phylogeny  is  an 
unusually  difficult  task.  One  tliiii;,^ 
however,  seems  certain  from  their  de- 
velopmental history,  and  that  is  that  tliey 
have  been  derived  from  primitive  bilat- 
eral forms,  and  that  the  radiality  charac- 
teristic of  the  adults  has  been  secondarily  acquired.  The  larv*  are  strictly 
bilateral,  there  being  indications  that  originally  two  water-pores,  situaled 
symmetrically  upon  the  dorsal  surface,  existed.  The  first  question  to  he 
decided  then  is  the  cause  of  the  radial  symmetry  seen  in  the  adult. 

Bilaterality  in  the  animal  kingdom  is  usually  associated  with  an  antoro- 
popterior  differentiation,  and  this  with  a  definite  axis  of  progression,    'i'lnis 


TYPE  ECHINODERMA. 


691 

become  specially  provided  with  sense  oZTf'  m"^  ^^"^^^'^^"tly  it  has 
new  conditions  whether  favorable  ouJro'''  ''''''^^''"  ^^  ^h««« 
affecting  the  dorsal  and  ventral  su^facf^^^^^^^^^^^^  '"!"''*'''^  "^«  conditions 
dorso-ventral  differentiation  exists    „..  ?*"''"'  ^"^  consequently  a 

affecting  the  two  sides  ofXb    'y     ^^l;"  o  ? " T^  '"^'  ""  ^''"'^^«- 
the  differentiations  which  occur  on  each  side  If  h'  "'''''  ""'  c««««q»ently 

con^:^::;^-:  ^~  ^^"  ^~tr  ^^  -^^^ 

.-sion  or  w^atrod^ ^i^rar  fh'e  ^^"^  """^ ^  ^f  pro- 
radiahty  of  the  Echinoderms  may  b  Ihe  re  u  ^  ^  f^^''''  ''''''  ^^^^  ".e 
larva     The  majority  of  recent  /ch  noderrarp   >  "^f""''  ''  "^^  ^^^^'^''^l 

f?rr  '^•^  '"^"^  ««^i'«'  but  it  wm  be  fouTd  I  'I  '"''  ''''  ^«™«'  t'^e 
foms  are  the  latest  to  appear,  and  tC  the  Pp,.        *  geologically  the  free 

actenstic  of  the  Paloeozoic  ro  ks.      Ths  would       T'"  "'"'  ^^P^^'^"^^  •-'''ar- 
0  be  regarded  as  the  most  perfect  representltir''  "^ ''"' ''''  ^"^^^^^^  ^^e 
he  ancestral  types,  an  idea  Ihich  is  borne  on/h      """"""^  '"^^^"^  ^^r^n^  of 
derm  development.     Thus  the  calyx  of  the  p"^ '''.       ^'^"'^  '"  ^^^^^^o- 
posterior  portion  of  the  oval  larv^  fh       *''^^"'^o^d  is  developed  in  the 
|hest,a,k;  intheBrachiolarTain/SuteLtr^.r"^"  '^'"^  ^-P-^ t 
1"  the  posterior  portion  of  the  larl  'ti/         '•"''"^' '^'^'^^'^  ^^^Wd 
<absorpt,on,  an  arrangement  which  mivt  '"?•''  P"^"«"  "ndergohig 
originally  the  adult  forms  Jh\T       ^       ^^Plained  by  supposin/that 
-ondarily  acquired  ^TJ :oZtTlaZ''''^^  werellk^l  t 
appeared,  the  body,  corresponding  to  the  calvvf.f  '  '''"^^  *^«  ^^alk  dis- 
"ig  in  Its  accustomed  position  i,f  .t  ^    ""^  ^^^  ^""oid,  still  develon 

the  Holothurians  there  n'rap;"^^^^^^^^^  o^  ^Le  lart    Ta 

posterior  regions  in  the  larva  Xh  oS  ^^^^^'^ction  into  anterior  and 

noted  that  in  the  young  ^^^1  1?'  '"^  T'  ^*^™«'  ^ut  it  is  to  be 
Pi^oral  lobe  which  late'  on  drppelfanr^^^^  ''"^  ^^  ^  well-marked 
aborted  stalk  region  of  other  forms  """^  '"P^^^^^*  ^he  partially- 

thuriaraTa'Sr  typfan^d  t^  ^.^  ^^^^^^  ^^^^  the  Holo 
Gephyrean  worms,  the  preL„  e  of       I -f,  o^^^^^^  ^--»^  ^orms\!t 

'"g  a  possible  affinity.     Or  a^r^in  ^f'P  "'^^^^^  ^rees  in  both  forms  suireesf 
tentacles  has  been  coLid^t^"  tit      ''^"'^'-^'-l-d  larva  v"ft 
various  groups  of  Echinoderms    ZT     ^^'^"'""^on  ancestor  for  all  the 
ypothetical  ancestor.     Nei'iTr^nhes:  Wew'T"^  '^'"^  ^'^^  '" '' 
to  the  origin  of  the  radialitv  and  thpT.      /       '  ^'^^^''^••'  'Affords  any  clue 
-  Widely  from  that  of  the  o^C^^  .hluTf  ""  ""'^^'^""^^  '^'p- 
hem  as  most  remote  from  the  commnn  ''"'  ^'''^fe'-able  to  consider 

the  Pentact^a  it  is  difficult  to  undV^f"''  ^"^'hermore  as  regards 
similarity  in  structure  of  the  d iff  f.  ^"^  '^''^  «''""Jd  be  so  1,1 
dopendenMv  f,-         v,  different  forms  if  thnv  ail    vwv  " 

Frnl.^        "  '^''  ''^™'n«"  ancestor  ^  ^"  ^^'fferentiated  in- 


592 


IN  VEUTEBRA TE  MOliPUOLOG  Y. 


stalked  form  for  an  ancestor,  and  to  consider  the  Crinoids  as  approaching 
it  more  nearly  than  any  other  recent  forms.  It  has  been  suggested,  with 
no  little  reason,  that  the  Cystoidea  were  the  ancestors  of  the  Crinoids  and 
perhaps  of  most  of  the  otiier  groups  as  well.  A  full  consideration  of  tiiis 
point,  as  well  as  of  the  details  of  the  conversion  of  the  bilateral  remote 
ancestor  into  the  radial  form,  would  carry  us  beyond  the  scope  of  this  woik, 
and  reference  must  be  had  to  special  works  treating  of  these  questions 
(P.  and  F.  Sarasin,  O.  Btitschli). 

As  stated,  the  relationships  of  the  Echinoderms  to  other  groups  is  a 
question  which  has  not  yet  been  satisfactorily  settled.  Attention  may  bo 
called,  however,  to  the  remarkable  similarity  of  the  jTornana-larva  of 
Balanoglossus  (p.  606)  to  the  Echinoderm  larva,  a  similarity  so  great  as  to 
suggest  affinity.  Tliis  suggestion  may,  however,  be  postponed  until  the 
Tornaria  has  been  described. 


SUBKINGDOM  METAZOA. 

TYPE  EGIIINODERMA. 

I.  Class  CuiNOiDEA.— Usually  stalked  ;  with  ten  (or  five  )  arms,  provided 
with  lateral  pinnules,  arising  from  the  margin  of  the  cup-shapi'd 
body.     Dermal  skeleton  well  developed. 
In  adult  life  free-swimming.     Antedon,  Actinometra. 
Fixed  throughout  life,  stalk  with  numerous  whorls  of  cirri. 

Pentaorinas. 
Fixed  throughout  life,  slender  stalk  with  cirri  either  wanting 
or  only  on  distal  joints.     Efiizocrinus,  Calamocrmus,  Hijo- 
erinus.  Thaumatocrintis. 
Fixed  throughout  life,  stalk  short  and  stout.    Holopus. 
II.  Class  AsTERoiDEA.— Free  forms  ;  stellate  or  pentagonal  in  shape  ;  arms 
containing  ca^cal  processes  of  digestive  tract ;  ambulacra  limited 
to  oral  surfaces. 
Dermal  skeleton  reticulate ;  no  paxillaB  ;  anus  present.    Aste- 

rias,  Brisinga,  Asterina,  Zoroaster. 
Dermal  skeleton  of  separate  plates  ;  paxillae  present ;  no  anus. 
Astropecten,  LuicUa. 

III.  Class  Ophiuroidea.— Free  forms;  stellate  in  shape  ;  arms  not  contain- 

ing ctecal  processes  of  the  digestive  tract ;  ambulacra  limited  lo 

oral  surface  ;  arabulacral  ossicles  contained  within  the  arms, 
1.  Order  OpJnurida.— Arms  unbranched  ;   madreporiform  tubercle 

on  mouth-shield.     Ophiura,  Ophiolepis,  Amphiura,  Ophiartis. 

Ophiothrix,  Ophioderma,  Ophiomysca. 
3.  Order  Euryalida.— Arms  usually  branched  ;  mouth-shields  not 

well  developed  ;  usually  several  madreporiform  tubercles.    As- 

trophyton,  Trichaster. 

IV.  Class  EcHiNoiDEA.— Free  forms;    without  arms;    test   composed  "f 


TYPE  BCHINODBRMA. 


593 

3.  Order  Clypeastroidea.-^mhul^^v^  aU  similar    limitP.l  f     ., 

3.  Order  -^e^afosWe/ta. —Ambulacra  Tnnr«  «..  i 

to  the  aboral  surface    mouriT  . ''!  dissimilar,  limited 

eatery  apparatu    v^nC;     ^  ■  t  "Z  T'  """"T''''  ^  ''''''- 
V.  Class  HoLOTHURoiDEA. -Free  fo'rmfo^;  ^P<^iangus,  Brmopsis. 

Tenmcte  toanehed  dendritically.     c„;„„„,.,,,  ^,„,,  y,.^. 

Teneacles  pinnate.    Bliopalodina. 

3.  Order  ^ixxfe.-Bilateral  symmetry  not  well  marked  •  =,.- 

not  oi^ning  to  exterior ;  tnbe-feet  wa,"l  '  ^tone-canal 

Respiratory  trees  present.    MahiMlia 
Eespiratory  trees  wantinjt.    Synapta,  CUrodota. 

LITERATURE. 

OENEKAL. 


694 


INVEHTSBHA  TE  MOliPlWLOG  Y. 


der  Echinodermen.     Ergtbuiase  uulurwiss.  Forschuugcn  auf  Ceylon,  i, 

1888. 

H.  Bury.     Studies  in  the  Embryology  of  the  Echiiwdenm.     Quiirtorly  Jouru. 

JMiiiosi'op.  tjcii'iice,  xxix,  1881). 
M.  Neumayr.     JJii;  SUiminf  dcs  Thuneichx,  etc.     Wicii  u.  Pnig,  1889. 
L.  Cuenot.     Etudes  ■norphoLoijiqucs  sar  ks  Echinodermes.    Archives  do  Uiulo- 

gie,  .\i,  1891. 
0.  BtttBohli.     Versuch  der  Ableilung  des  Echimdertm  aus  einer  hilateralen  Ur- 

fona.     Zeitschr.  fl\r  wisseiiscb.  Zooiogic,  uil,  Siippl.,  1892. 
H.  Ludwig.     Eehinoderuien.    Biouls  Klasscii  uud  Orduungeu  des  Tliierreicbs, 

III.     (Ill  course  of  publiciitiou.) 


i 


CKINOIDEA. 

W.  Carpenter.     Memoir  on  the  Structure,  Phi/xiologi/,  and  Development  of  Ante- 
don  rosaceus.    Pbilosopb.  Truusiictious   Royal  Society,   Loudou,  clvi 
1866. 

H.  Ludwig.  Jicitnige  zur  Anatomie  der  Grinoiden.  Zeitschr.  fUr  wisseiiscii. 
Zoologie,  x.\viii,  1877. 

A.  M.  Marshall.  On  the  Nervous  Sgntem  of  Antedon  rosaceus.  Quarterly 
Jourii.  Microseoj).  Scieuce,  xxiv,  1884. 

E.  Perrier.  Metnoire  sur  I'organisation  et  la  d/'veloppement  de  la  Comatule  de  In 
Mcdit^rranie.  Nouvelles  Archives  du  Museum  d'llist.  Nat.  de  Paris,  2"" 
sC-r.,  IX,  1880  ;  S""  ser.,  i.  1889  ;  ii,  1890. 

H.  Sury.  Tfie  Early  Stages  in  the  Development  of  Antedon  rosacea.  Philoso- 
phical Transactions  of  the  Royal  Society,  London,  clxxix,  1888. 

0.  Hamann.  Anatomie  der  Ophiuren  und  Grinoiden,  Jenaische  Zeitsdn., 
XXIII,  1889. 


i 
.      i 


ASTEHOIDEN. 

A.  Agassii.     The  Embryology  of  the  Starjish.    Memoirs  from  the  Museum  of 

Com  p.  Zool.,  V,  1877. 

H.  Ludwig  Beitrdge  zur  Anatomie  der  Astenden.  Zeitschr.  fQr  wissenscb. 
Zoologie,  XXX   1HT8. 

0.  Hamann.     Die  Asteriden.    Jena,  1885. 

L.  Cuenot.  Contrtbutions  d  I'ttude  anatomique  dcs  Asterides.  Archives  de  Zool, 
e.vpcr.  et.  gen..  2">'  ser.,  v,  1887. 

0.  W.  Field.  Th,  rarva  of  Asteriaa  vulgaris.  Quarterly  Jourual  of  Micro- 
scop.  Science,  xxxiv,  1892. 

ornn7noiDB.\. 

Th.  Lyman.  OpJiiurida  and  Astrophytidiv.  lllustr.  Catalogue  Museum  Coiup. 
Zool..  1865. 

B.  Ludwig.    Beitrdge  zur  Anatomie  der  Ophiuren     Zeitschr.  fUr  wisscuscb, 

Zool..  xsxi.  1878. 

H  Ludwig.  Das  Mundskelett  der  Asterien  und  Ophiuren.  Zeitschr.  fUr  wis- 
senscb. Zool.,  XXXII,  1879. 

H.  Ludwig.  Neue  Beitrdge  zur  Anatomie  d$r  Ophiuren.  Zoiischr  fQr  wis- 
senscb. Zool.,  XXXIV.  1880. 


TTl>ll  KCmmDKHMA 


/i95 

xxm,  1889.  ^mmen  u,ul  Crmoiikn.    Jcuaiscbe  Zeitsclir., 

E.  W.  MaoBride.     7%e  Development  of  tJie  (Umtni  n 

and  Aboral  Sinuses  in  Amphium  1  ^'"f"'^^7«"*.  Ovoid  Oland,  Axial 
euce.  XXXIV.  1892.  '     '•    Q'^'"t«''.V  Jour.,.  Alicrosco,,.  Sci- 

ECHINOIDEA. 

;■  "M^t- ,£ rrrMlsi^r,^'  *  *  —  - .» ,„. 

■    S...f!"t^.'"'  "•   *"•■'•*••     K»"8>.  8vo„a..  Vetc^k.  A.„„ 

UOLOTnnuoiDKA 

0.  Hamann.     Die  Ilolothurien.     Jena,  'ibn/' 
H.  Ludwii     Die   ^.„n,,  ' ,       *-'^'''-"- '^<«j'"«:ie,  Lvn.  1894. 


596 


INVERTEBRATE  MORPHOLOGY, 


CHAPTER    XVII. 

TYPE  PliOTOCHORDATA. 

The  type  Protochordata  coutaiiis  a  u umber  of  forms  which 
present  certain  features  of  similarity  to  the  Chordata  (Verte- 
brata),  oue  member  of  the  type,  AmpMoxus  beiug  frequeutly 
cousidered  as  belougiug  to  that  group,  which  is  to  be  regarded 
as  the  most  highly  ditfereutiated  of  all  the  types  composing 
the  Animal  Kingdom. 

The  various  groups  of  the  Protochordata  differ  greatly  in 
general  appearance,  but  certain  structural  features  of  great 
morphological  importance  are  common  to  all  of  them.  These 
may  be  briefly  stated  as  (1)  a  notochord,  consisting  of  a  more 
or  less  well-developed  rod,  arising  from  the  mid-dorsal  line 
of  the  digestive  tract  and  either  extending  the  entire  length  of 
the  body,  or  else  limited  to  its  anterior  or  its  posterior^part, 
or  even  present  only  during  larval  life,  as  in  the  majority  of 
the  Tunicata ;  (2)  hramhial  slits  which  place  the  cavity  of  the 
pharynx  in  communication  with  the  exterior  and  serve  us 
respiratory  organs  ;  (3)  a  central  nervous  system,  situated  in  the 
mid-dorsal  line  of  the  body,  and  arising  in  some  forms  as  an 
ectodermal  invagination. 

Metamerism  is  but  feebly  indicated  in  the  majority  of 
cases,  some  forms  possessing  only  three  mesodermal  somites, 
while  others,  such  as  some  of  the  Tunicata,  show  traces  of 
it  only  in  the  posterior  region  of  the  body,  AmpMoxus  being 
the  only  form  in  which  it  is  at  all  well  marked.  Limbs 
do  not  occur  in  any  members  of  the  grouj),  nor  are  there  auv 
special  jaws  or  organs  of  mastication.  All  tlie  members  <if 
the  group  are  marine,  and  the  various  classes  i)ossess  a  wid.' 
geographical  distribution. 

I.  Class  Hemichorba. 
The  members  of  this  class  are  characterized  by  tlie  noto- 
chord  being  a  com])arative]y  small  diverticuhnn Of  the  an- 


TYPE  PROTOCHOHBATA. 


The  bod,  i.  divi»w;ire:~:-t''  t  "^'"'''^''«-- 

epistome  or  proboscis  a  ms,);.!  ?J  '  ""'erior  praoral 
visceral  sac  or  U^^^^^^^  ^^'  -f-..»<l  a  posterior 
oorrespoudiug  regious  a  nair  of  ,  T  °'"  "'  '""''«'»  i"'o 

'wo  additional  pores  Derfnrl  ,     exterior,  while  one  or 

or  proboscis  cavtt       ^rleZZ,       '\°'^''<>  '"  ''^^  ^l'-'"- 
tion  with  the  eeto^lerm  and    Z,       '^   "f  '■'"""""  '"  """"ec 
m  the  collar  region  ''  P""""""'  P""""  i»  situated 

'•  Order  Pterobranchia. 

(^pMCl'lClttl  oocJZ.TT"'  ^''^r^'^^ra  and 
"f  Norway,  while  the  latte^wL  obLl  A' "^  ^^'""'  °"'  ""^  '"""* 
Expedition  in  the  Straits  ofTaget:        '  ""^  "  ^'"'"'^"«-- " 

'""*^""^"^'l)--,oniaH„rn..  consisting  or  a 


stolonhko  systoni  „f  tubes  ru„„-f  • 

»'"ues,  etc.,  and  Kiving    ff  ^0,^  Y?  'T  "'"  "'"•'»-">  "f 
»lich  c„„t„i„„  .'^.  ;  t'.  . .  "'""'"'•  'atorul  tubes  e„,.l,  „,,_     J 

-l..tmlike  material  and  fonn 'a  " hou 'r-7 ,'""  ~"'1"'»«'  "f 

"     '"'  "'f  <">l"i'y.  and 


598 


m VERTEBRA  TE  MORPHOLOG  Y. 


are  traversed,  except  towards  the  extremities  of  the  latorul 
tubes  where  the  iudividuals  occur,  by  a  chitinous  rod  which 
results  from  the  chitinization  of  what  was  ouce  the  stem  of  the 
various  polyps.  Each  of  these  J-  stalked  (Fig.  272),  the  stalk 
(C)  becoming  continuous  below  with  the  chitinous  rod,  and 


Fio.  273.— iNDlvlDtTAl,  OF  Rhnhdopleura  (slightly  modlfled  after  Lankkster). 
(N.B.— Tlie  teiitiicles  of  oue  side  of  oue  arm  oiil^'^  are  represented.) 

B  =  iiiial  piipilla.  G  =  tentacle. 

C  =  stalk.  Oa  =  arm. 

Z>  =  epistomc.  /  =  intestine. 

E=  trunk  region.  K  =  sensory  papilla. 

F  =  collar  region.  JV  =  notoeliord. 

each  consists  of  three  well-marked  regions.  What  may  ho 
termed  the  anterior  portion  of  the  body  is  formed  by  a  hii>,'e 
disklikc  iipistome  (/>),  beneath  which  on  the  ventral  surface  is 


TYPE  PROTOCUORDATA. 


("rr,;  ^^^^-r  r-'  '-^  -"-  -- 

processes  (ft,),  each  carry  L,r^,"''^'""'  '"»  '""S  •■'™'ike 
( O)  arranged  pinuately  'T^t  "d  '  ""  °'  "I""'"'  '-'"«>- 
(^;),  from  the  posterior  and  vL  .1  T"  '"  "'"  "''"""■"'  ^"<' 
arises,  while  dorsally  Ind  alrt  i'";"""  °'  """''  "»  ^''"'^ 

(li).  at  the  extremity  of  which     ,  '""™'  "  "°'"  P"?'"'' 

'I'l.o  ,i;      1-      .  "I'lcu  tile  anus  opens 

Jl'e  digestive  tract  consists  of  ,  <,t.    ■  T  . 
"■■"."g  the  collar,  and  liavkr,o,     r*'  "'«'"  «sopLagns  trav. 
-"•face  a  short  b  i„d  ,  re"s   ^l  1        '""'■  "  ""  "'«  'l''''™' 
with  that  of  the  ceso,  1  Zs      T    "''.'"'!, "''" '3'  communicates 
cl'ord.     The  «sopha  ~ns  fnto  f /'^  """'"-taiy  ii„to. 
fromthelowerendof  wliiXh.,?   r^'^"  ""''"«'  "'"'"ach, 
i-K  "Pou  itself,  runs  frrwlrd,     '"        "'  ^'}  ""'''•  "■"'•  ''-<'• 
,     The  nervous  syst  m  co'dst  T:  tr  '  "  ™"'  '^»P'"- 
'lerm  on  the  dor.al  surface  of  ,t      M  "'"='^'""■'8  "'  «'«  ecto. 
found  a  small  ciliated  eWtiLlrT"  "'"^T'  ''''"''  '"  ■•''- 
->  other  special  se.ise-oi™':" 'cc  u^'T"  'r  "^r^'^''' 
collar  a  pore  occurs  which    hv  »  ,"'""=''  ^"^o  "I  the 

p.- torates  the  wall  of  the  bodv  ,  [,  '"'""^''  """'  '"'"d' 
i"  commiinication  wi  h  tie  e  tSri  "  "'"'r  "'  ""'  <=""- 
.•epresentingaiie«retory„r,4n  Z'  1  ""^  '"'  ''"«"'''=''  ■■« 
slits  have  yet  been  observed        ^° 'I"«""™-P°'-e  or  branchial 

".e  house  is  gelutin  uT'ntut  "^""'V"  t>eing  colonial,  but 
»l'ort  stalk  do  not  eni'ain  ' '  '":■'■"  '^'"'''  '"'"'"'  ''■""'  "'e 
early  separate  from  Z  pa"r"E  1'"  "i"'  ^"''  ""-■•  ''"' 
xists  of  three  regions-al  ^1^  ''"'•'''  <^'«-  273)  con. 

a  large  epist,,,ne^  a     idX  CO     1  ,7™'"''"\P"'''"" '^''i"'' f^^ 
-c ;  the  body-cavity  b  in,"  i  ;  ,!*^'™l'''':  "  P"^'""™  "■"ceral 
-«iouB.     Two  epistle  ;o^er:;te       ",  7"-'>"-'-« 
tl.e  c»lom  to  them  passii  g  tl  ro  ,g    't  ^T:?"'  ''"'""«  '■""' 
awvons  system  („).    The  dnr»!  '"""''  I""''  "'  tli« 

i»  thickened  to  f  ,rm  t  e  ceZ  „"  ""  "'  ""  """'"•  ••««'"" 
»i'le  of  this  is  a  cluster  of  kLr'T'%"'''''"'  "'"'  ""  <«"^1' 
l'"'Wike  dilatation  a,  ,1  Larii'  , "  "''  'f'  '""""«  '"  - 
•'"■angediii  two  rows.     At  m"  ^^."""^""M'"--'"   1'""".Ich 


At  tlie  aides  the  coll 


-'<-  an  ,1  pairoi  luternl  folds  whi 


ar  iM  iv.i.f.' 


•luuOU 


'•"itorior  portiou  of  the 


li  slightly  overlap  the 


VLsceral  sac  and  for.n  the  operJ^Z. 


600 


IXVERTEBRATE  MORPllOLOG Y. 


A 


I  i 


w 


\  I 


upon  the  inner  surface  of  wliicli  there  is  on  each  side  a  colhir- 
pore. 

The  mouth  (m)  opens  beneath  the  epistome  into  an  esoph- 
agus, which  iu  the  collar  region  bears  a  dorsal  cliverticuluin, 
the  notochord  {x),  projecting  forwards  into  the  epistome,  In 
this  same  region  !^'ere  is  on  each  side  a  branchial  slit  {sp), 
structures  v  !.;.!■  're  apparently  wanting  in  lihahdopleura. 
Behind  the  a        „u,gus   opens   into  a  saclike    stomach  from 


Fio.  373.— DiAGUAMMATic  LoNoiTruiNAT-  Srctton  TiniouGH   Cephalodiscus 
(after  Ehi.eks  from  Kokschelt  mikI  Heideh). 
a  =  anus.  n  =  nervous  system. 

ex  =  excretory  organ.  sp  =  branoliial  slit. 

g  =  ovnr3\  t  =  tentacles. 

m  =  mouth. 


X  —  notochord. 


which  the  intestine,  bending  upon  itself,  passes  forwards  to 
open  (a)  upon  the  dorsal  surface  of  the  visceral  sac,  a  shuit 
distance  behind  the  collar. 

The  collar-))ores  probably  serve  as  excretory  organs,  ami 
it  has  been  stated  that  the  epistome-pores  open  into  well- 
developed  tubes  (ex)  terminating  in  the  epistome  cavity  in  a 
dilatation  ;  they  also  have  been  regarded  as  excretory.  The 
reproductive  organs  {(/)  are  paired  sacs,  which  c^peu  on  the 
dorsal  surface  just  in  front  of  the  anus.    No  circulatory  system 


ide  a  collar- 


601 


TYPE  PltOTOCUoUDATA. 
-"tailed  i.  the  order.   '"^^^^^^'-^^  -^  -tLer  of  the  l^ 


:   Cepliolodhi'M 


^,  ^-  ^"'^^"  Enteropneusta. 

xlie    o)'der   T^nf 

'"  »tn,c-ture  over  iL  Pterob.r  i        !       "  "'«<''''<«'  ^'Iva-u-e 

'>•-« M  ami  the  au„s  t«-„,i„af    Til  "'f  ■'"''"«  l'"'clical]y 
'"<b-  (F.g.  274,  p,,  ,„,  „,^  ,    :     "«'"";„,„.  portion  of  t,i 

""■'-"  to  the-^eoon!'  4  :';;::  t  "-  P'«-.'>.a.'c,,ra  ,■ 
«1  surface  of  wl.i,-!,  is  a  „  1  ,  ""'■'■""■  '"''^'  '>l".u  H,e  ,]„; 
«-  p.'"bo...i..„,„.„„    ,-:  '„  :;X';;-".v  t.o)  „,,el,  ,„a    ', 

»'".'«  "l'»"  it«  ventral  .surfa  e  i^       ""'    !""'   *''«   -'''«io,, 
■■-«;<;..,  i.s  the  „,o„tl,.  "'  '""'  "^'^'^  "  J'-i-^s  the  second 

J^ije  second  remo,,  ic,  „ 

'■""-■(«),  it.  post;;;:.  „,z'br  "■'."'""■'  ='■"'  f-"-  «- 

■■«o..t  distance  in  the  fo       T^Zl"''^''  ''-"-«!«  i".' 

;""    "'«  «i-l-  "t  the  «nterio    ,;:,:"■''?.  ""^''-  ""-■  -alls 
«>;Iy  a  space  ,vhich  connn  ,„':'"' ,''f  .";'■''  I«"«™  "f  the 
I     le„oran,Iislnown„s  the       ',!■     T.  I""'  "-'.V  «ith    the 
«.on  of  the  bo.Ij.  is  „„.eh  hthan     ■/;""'"'"'■  "■■  """k 
:  «""••"■  ■■"Kions,  and  contains  H  """"'  "'»  l'"'l'o»<-is 

'''««st.ve  tract  and  the  re    t    ,  r        *'"'""""'  l"""'""  "f  the 
;:""■     '»'  fattened  and  e::;'::"«r\  ^■""'"'b' it  i 

"Ise,  on  either  side  of  ,vh  ..hll  tn  ,      ''"   ''"'•'''''   ^'-'face  a 

;: '!;!'v-ve  tra:!:!:i;-:;;:r^^^^^ 


iiicr 

lienor 


■ea.se 
ones 


I1I<!<. 


1»  milllber  .] 


J^^iiff  merely  circu] 


branchial  slits.     TJ 


liev  sp 


^;^"  Jife  of  the  amma],  the 


ar  () 


eenj 

1)08- 


'i^eniugs,  as  the  anterior 


602 


INVEHTEBRA  TE  MOliPUOLOO  Y. 


4 


^' 


ones  are  in  the  younger  stages  of  development,  a  tongueliko 
valve  later  growing  down  from  the  dorsal  border  of  the  pore 
and  giving  it  its  U-shaped  form.  Water  flows  in  at  the  mouth 
and  passes  out  through  the  branchial  slits,  which  thus  pos- 
sess a  respiratory  function.     A  few  of  the  anterior  slits  open 


Fig  274  —Balanogloasus  Kowalewskii  (after  Minot  from  Spenqel). 
br  =  "biaDcbiul  slit.  c  =  collar.  pr  =  proboscis. 

externally  into  the  atrium,  being  covered  over  by  the  back- 
wardly-projecting  atrial  folds  of  the  collar,  but  the  majority 
are  quite  uncovered  and  are  plainly  visible  from  the  exterior. 

The  ectoderm  contains  numerous  mucous  glands  and  is 
ciliated  throughout,  no  external  cuticle  or  "  house,"  such  as 
occurs  in  the  Pterobranchia,  being  developed.  Below  it  rests 
upon  a  thin  basement-membrane. 

The  coelom  is  clearly  marked  out,  and  consists  of  three 
portions  completely  separated  from  one  another  and  corre- 
sponding to  the  three  body  regions.  The  proboscis-co'ldui 
(Fig.  275,  A,  pc)  is,  in  its  anterior  portion,  a  simple  unpaired 
cavity  lined  with  delicate  cells  and  traversed  by  circular  jiud 
longitudinal  (hn)  muscle-fibres.  Posteriorly  it  is  prohniKeilj 
into  two  horns.between  which  lies  a  mass  of  tissue  consistiugi 


l-rVB  I-BOTOCUOIWATA. 


of  several  different  oiKans     tt  .  "'"  *""^ 

"  f"«»'<lly-.JirectecI  d  vertical  ;/", '"  ""^  P'^'ol'.-auebia, 
»ten„r  portion  „,  the  di2^^eT.- 1       >        "''  ^'"'"  »'  "'« 

bIIt?^'  cavity  eo.a,,,utCL„  w;;*:  tT.'r" "  "■"- » 

I^O'sal   to    the    uot,«h„rd    lies  »"'""' ™«l'''»Kus. 

;'  fo>r'  "'• '"  «o,„e  oases  many "  '  t?     ' ,"  '""  ^'"^  e„„taimus 
l«««B.vesie]e,  as  it  has  bee    fe™        J"'  "'"'""""•     '^'''"  l»o- 
>"'tion  of  the  prob,,scis-c„lor  V  ;vT'''''''m ''''^''■"''■■--■'t  a 
"o  separate  cavities,  oril ' ,  ^  ^'" ''  "■""'''  '!«'"  consist  of 
«comes  very  iar«e  aid  i'        fe'f  "'"'  '^"-  ""e  of  which 
«-««.  while  the  other  rem-^Z  ^ .     '  ''"'■"""  "^  "'e  I^'o- 
I'e^e   structures  are  a  mZ    ;<,?'"!/""'"•     S»"ouu<{iug 
ajersof  the  proboscis-cJ™    ("y"."''  "^  ""^  BUauch.it 
b'^e  m  the  folds,  while  tl^Tel Is  i'       ■'"  "^    •''""''■vessels 
"'"tarn  yellow  ,„.,„„,^^  ,  l"\!r""«  "'"»  frequently 

Sianules  indicate  a  Klaudul!,  f       .  '^"Pl'osed  that  these 

*'<"ently  the  entire'la'^i'fi™:^    ""'  ""  '"'''''■  ""      " 
''"scis-ghmd.  '°'''''  ''"^  I'eeu  teriued  the  pro- 

The  coilomio  cavities  of  *l,         i, 
"■""''•  ••»«  umch  siu   rr  al        '''"'"'  ^^'«-  ^^S,  7/  cop)  and 
"«'"  and  left  sides  bS^  se  L!"ed'fr"'''  "f  """'^^  °^ 
-J  ventral  mesenteries."  iC  tt    '  "  7°''  ""'-•  ''J-'Io-sal 
"■•»  end  of  the  trunlc-cceh  ,„    „"     ' '?"'  '^"'■«'"'  "'  the  an. 
•»'•<'  '"to  the  collar.  ]yin,,  '"  '"V   "'""«""°™  extend  for- 
---1  a„,I  ,„„„i„^,  t  «  petil™,,  d      "■  '  "'  ""^  '•™-'"  '''ool. 
;;'■■<;'' are  longitudinal  ,,„     Ifih    """t^"  '"  ,"■«  '"'-ior  of 
"";■''  I'^'l^Kation  of  the  tr„uk„lll  ,    T  •"''"■  ^'""'--  '''■- 

--"-'-..ophagus,  fort-^r  ;5;:-^^^^^^^^ 

'""ar  and  trunk  of  a  dorsa  ''"'"''  <=°"«i»tHig  in  the 

!■"■  '>i«tin.t  n,u.eui:r  ™     ,  '  H .,  T'!"'"' .  '™Si'-Ii"al  ves 
P'<""  the  dorsal  vessel  bm  ch'e        ^"'^'  '"  "'"  ""■"enteries 
;'•»«  of  the  branchial  s  i  s  T,  d  1!,""'     ',"''  '™«"'^'"'-  I'«- 
"vard  into  the  proho,,,:'  "t"     ^r    ",""  '"  ™""''-J 
'----^  -  t^e  "otochor^rir ^^-n,-,J- 


604 


IN  VERTEBRA  TE  MORPHOLOG  Y. 


t 


The  bloocl-spiices  iu  the  proLoscis-ghmd  commuuicate  with 
the  heart,  aud  the  dorsal  aud  ventral  vessels  of  the  collar  uinl 
truuk  are  imited  by  a  double  set  of  tine  lacunar  capillaries, 
one  set  being  situated  in  the  body-wall,  and  the  other  in  the 


cop  —  colliii-cceloin.  ' 

(j  —  tongue- bill-  of  skeleton. 
]i  =  lieurt. 

Jal  =  bnuicliial  valve. 

kh  -  bnuichii.l  portion  of  oesophagus. 

ks  —  bnaichial  septum. 

kp  =  branchial  porv. 


Im  —  loiigiiudiuul  umst'les. 
nc  =  uotoeliord. 
nd  =  dorsal  nerve. 
no  =  ventral  nerve. 

0  =  a-sojiiiagus, 
pc  =  pioboscis-coeloui. 
pfl  —  proboscis-gland. 


ps  =  proboscis-vesicle. 

wall  of  the  intestine.     The  blood  is  a  colorless  coagulable 
fluid,  apparently  destitute  of  corpuscles. 

In  the  posterior  portioJi  of  the  proboscis  is  found  a  plate 
of  chitiuliko  material  produced  into  two  horns  posteriorly, 
and  frequently  somewhat  hollowed  out  in  front.  It  is  evi- 
dently supportive  in  luiietioii,  and  forniK  the  proboscis-skele- 
ton. In  connection  with  tlie  branchial  slits  a  similar  chitiiioiis 
skeleton  is  formed  (Fig.  276)  consisting  of  a  series  of  tiiii 
verse  bars  placed  cn'er  each  septum  between  adjacent  slits 
From  the  middle  of  each  bar  a  rod  (really  double)  passi 
down  each  septum  (.sA),  ixJuI  from  the  extremities  a  bar  (// 
passes  into  each  of  the  adjacent  tonguelike  calves,  each  valv. 
thus  possessing  a  ))ar  from  the  arch  lying  in  front  of  it  ;;ii' 
another  from  that  lying  behind  it.     The  septal  bars  ami  ti 


is-l 


TYPE  PliOTOClIORDATA. 


tlie  bruiichin!  slits.  ^^^"'^  ^^'^"'^^  tl^^  valves  of 

;'"'-'":.-<I.  wind,  exte,!'    , 

"'."-."'it,  to„„i„,,,  ,,„,,; 

l^^.*  l.mcticall.v  obliterated  u; 
"'"  ™^""'i=''.ti0B  ami  e„la,-.-e! 

ami  «  Im-h  are  coutim,o„s  will, 
i'e  ea.l„,,er,„al  Ji„ia„  ,„•   ^l 
;  'S-tn-e  trae,    J,,  t,,,.",,,,,, 

;-"<4.al.sii...aIrea,,,referre 

of    I,  '      f'""'-'"'"'''  l-"vti„a» 
"    the  >ate«t,„e   (Fi,,  275,    /• 

«)  auJ  eventually  opening  t„ 
■■'»rfy  i"  soa,e  species  the  wall  A^  'i""';.^'^^''-  ^^f'"'''  I'"«'«- 
';;*o  »ac„„lati„a,  .Lie,,  have   ,  e  '  f',""  '^  ''"""'""'  "»' 

""»'"«  m  the  ,„id.lle  of  the  liv'  '''?•'•""'''»""''  «•«".•», 

'"ee  of  the  i„te.,ti„e  i„  the  for. f   /",'","  *''""'  ""^  ''"'■'"'1  »"■■ 
.'■""■'3'.  "Pe,«  a«ai„  i„t ,  t  ie  « ,  ,"  '"^'  "'-".  '"--  p.«te. 

-i.testi„e  of  eertai,,  A„„eli,      f  v      '         '""''""  "'"  "ccessory 
'"■'  i»  P«,„har ei„,      „i  .r''''-'?;^'"-  ""''  Echiuo.Ier„,s 

«'«.  «ter.„r    have  hee„    fo,„„       ,,•""'"""'"'"  ""1' 
«"™.»  at  present  „.li„v„  "'  ""'■*'"■•«•   "'«■•  «i«uifl. 

'"'  '■l<'"8atVd''errriv!Crrt!,e''n,n'  i'  '"?""  '"  "'«  f<""'  "f 
l-.^ion.   with  the  eel..,,;,,:  o    ,     '  h  iT"'  "™  "'  "'^  »"-"' 

'  "  "*   '"  oouuectiou  at 


■''  ^  syiiiipiicula. 
tb  =  toiio-uf  Ijjir. 


t\ 


606 


INVERTEBRATE  MORPHOLOGY. 


either  end,  though  free  throughout  the  greater  portion  of  its 
length.  It  contains  in  young  forms  a  central  lumen,  which 
may  be  represented  in  adults  by  a  series  of  separated  cavities 
and  which  results  from  its  formation  as  an  invagination  of  the 
ectoderm.  From  this  dorsal  cord  a  plexus  of  nerve-fibres 
extends  all  over  the  surface  of  the  body,  lying  in  the  lower 
layers  of  the  ectoderm  and  being  at  certain  regions  specially 
developed  so  as  to  form  nervelike  thickenings.  One  of  these 
surrounds  the  dorsal  and  lateral  surfaces  of  the  base  of  the 
proboscis,  being  perforated  by  the  proboscis-pore  ;  another 
occurs  at  the  posterior  edge  of  the  collar;  M'hile  two  others 
occur  in  the  trunk  region,  one  in  the  dorsal  (Fig.  275,  B,  ml) 
and  the  other  (wv)  in  the  ventral  mid-line,  extending  the  entire 
length  of  the  trunk.  No  sj^ecial  optic,  olfactory,  or  auditory 
organs  seem  to  be  developed. 

The  short  canal  opening  by  the  proboscis-pore  has  been 
regarded  as  excretory,  but  the  assignment  of  such  a  function 
to  it  seems  questionable.  A  similar  function  has  been  as- 
signed to  two  short  tubes  with  folded  ciliated  walls  Avhich 
communicate  internally  with  the  ccelom  of  the  collar,  and 
open  to  the  exterior  by  the  collar-pores,  situated,  one  on  each 
side,  on  the  edges  of  the  atrial  folds.  More  definite  informa- 
tion is  required  concerning  these  organs  before  they  ciiu 
finally  be  accepted  as  excretory ;  they  evidently  correspond 
to  the  collar-pores  of  the  Pterobrauchia. 

All  the  known  species  of  Ualanoglossus  are  bisexual,  the 
reproductive  organs,  ovaries  or  testes,  consisting  of  simple  or 
branched  pouches  situated  in  the  trunk,  beginning  in  the 
braucial  region  and  extending  some  distance  backwartls. 
Each  pouch  opens  to  the  exterior  by  a  special  duct,  upon  the 
dorso-lateral  portions  of  the  body. 

Development  of  the  Enter opnezista. — Some  species  of  Bahnio- 
glossus  (B.  Koivaleii'sldi)  develop  directly  without  the  iiitti- 
vention  of  a  larval  stage  in  the  life-historj',  but  the  majority 
possess  a  characteristic  free-swimming  larva  known  as  the 
Tornai'ia  (Fig.  277).  It  is  a  barrel-shaped  organisnj,  buli^eil 
out  slightly  at  either  pole,  and  possessing  a  locomotor  iijipa- 
ratus  in  the  form  of  somewhat  complicated  bands  of  ciiii. 
One  of  these  surrounds  the  posterior  portion  of  the  bu(l\  ;i^ 


TYPE  PltOTOCUOItDATA.  q^^ 

<'4^ex  of  the   body  in  an  ectocler-  ''     ""Z'''''  "*  "^« 

;;;f   f/f^^^i^^^    the   apical   plate 
(«)>  which  bears  two  ejes 

Tlie    moutJi    (J/)    opens    by   a 
s  ^ort  oesophagus  into  a  capacious  , 
«ton.ach  iS)^  separated  by  a  per!  '' 
forated    partition   from    the    short 
rectum  (i?),   which   opens    by  the 
terminal   anus.      In    the    anterior 
portion  o     the    body   is  a  saclike 

siucture(;,c),  united  to  the  apical 

Piate    by    a    muscular    band   and 

opening  to  the  exterior  by  a  pore  --^-^ 

O')  situated  a  little   to  the  left  of  ^^«- /^^-Tokkakia  Lakv.  o. 

tiie   mid-dorsal    line.     Thivj  «n     •      -^«^«"»^^o.wm«. 


«  =  apical  pliiie. 
cc  =  coilar-cffilom. 
^=  month. 

P  =  dorsal  pore. 

Pc  ~  piobobcis-coelom. 
li  =  reciiim. 
^  =  slomncli. 
ic  =  triiiik-ca^Jo^ 


t  ie   mid-dorsal    line.     This  sac  is 

the  proboscis-ccelom,  and  the  pore 

the  proboscis-pore,  and  in  connec- 
t  on  w,th  th    ,,^^  .^  ^  ^^^^^^^ 

the  so-called  heart,  which  becomes 
the  proboscis-vesicle  of  the  adult 

At   a     ater   stage  of  development  -  =  .n..,k.ea^,o„ 

t^vo  other  pairs  of  ccelomic  sacs  (cc  and  tc^  i  T' 
pearance  at  the  sides  of  fl.n  .  ^  f  ^  "'''^^'^  their  an- 
coHar  and  trunk  c^:'  '^Z  ""IZlf  '"'  ''"'  ''^^  '^  ^ '^ 
^-adual  transformation  of  this  h  v.  T  '\  '''^"""'^^  '^^  ^^'^ 
^netamorphosis.  ''''^'^'  *'^^^'^  ^^ing  no  sudden 

T^>^  Affinities  of  the  Hemichordatn     ri 
'>"t  that   tho  Pterobnu.chi.  ::,  te  -     7 '''^^ 
-;nanysi„nhu,,„a  at  the  same  til  ptu   ::"::?:  ""  f''^^^^^  ^•'^'^^^-^' 
-  h  grcps.     Thus,  to  mention  or.ly  some  i;  tl  "'"'      '""'  ^"""^^  "^ 

'>•>  "  Krou.^s  possess  a  notochorcl  of       "mil'  "'"'''  ''''^''^  '^^''^^'^^^ 

eollar-pores  and  branchial  slits  and  r  -.         ?  ■"'''''  '^''^'^^^^-i^-pores 

;'"■-  .stn-ctlv.con.parable  re^^ion       Th  «      I  "•',*';"'  "^^'""'  ^''-"-^  i"t(^ 


608 


IN VEIl TEBRA TE  MOliPHOLOG  Y. 


be  postponed  for  the  present,  and  attention  called  to  the  sugj^estivc  ehar- 
acterof  the  I'urnaria.  Its  first  describer  took  it  for  an  Ecliinoderni  larva, 
and  tiie  majority  of  succeeding  antiiors  have  been  inclined  to  regard  it  as 
indicating  aiiinities  with  that  group.  Tlie  arrangement  of  tlie  pneoral  and 
postoral  ciliated  bands,  and  the  occurrence  of  the  proboscis-pore,  suggest 
the  Ecliinoderni  larva  witliont  doubt,  but  it  must  still  })e  regarded  as  a 
decidedly  open  (picstion  whellier  or  not  these  fcatur'-s  indicate  an  alliiiiiy. 
Furliier  inforauition  is  recjuii'ed  both  in  regard  to  the  ancestry  of  ilic 
Echinoderms  and  as  to  tlie  life-histories  of  the  I'lcrolinmchia,  before  llu^ 
question  can  be  settled. 

Anollier  line  of  ancestry  niu.st  also  be  mentioned,  namely,  one  wliicli 
leads  back  to  ancestors  common  to  tiie  Ilemichordates  and  the  Prosopygia. 
The  similarities  of  the  Fterobrancliia  to  the  I'olyzoa  are  striking,  ilici'C! 
being  the  same  bending  of  the  intestine,  similar  lophophorelike  tentacular 
structures,  ami,  what  is  of  considerable  importance,  a  dor.sally  situated 
nervous  sy.stem  arising  as  an  invagination  of  the  ectoderm.  A  furihn' 
point  perhaps  of  some  imiKirtaiice  may  also  be  mentioned,  i.e.,  (he  occur- 
rence of  three  :>ectioiis  in  the  body-cavity  of  the  Brachiopoda.  In  following 
out  the  line  of  difscent  suggested  by  these  similarities,  we  are,  howevci', 
quickly  brouglit  to  a  halt  by  the  uncertainty  connected  witii  the  origin  nf 
the  Prosopygia.  and  we  ai'c  left  standing  Ix^twecn  two  lines,  one  leading 
back  to  till!  Prosoiiygia  and  the  other  to  tins  Echinoderms.  Whether  or  not 
the.so  two  lines  conv(n'ged  to  common  ancestors  in  pre-Cambrian  timo  can- 
not be  ascertained,  and  the  solution  of  the  problem  must  be  left  to  fuliue 
eml)ryi)logical  investigations. 


11.  Cl.vss  Cephalochorda. 

The  class  Cephaloclioi'dii  oontaiiis  a  single  <j;piius,  jlniphi- 
oxus  {linniclilosffntKi),  wliicli  is  cxt'lusivt'ly  marine  in  linliitat, 
bein<];  i'oiiiitl  linried  in  an  u])ri<;lit  j)()sition  in  the  sand,  the 
anterior  end  ol*  the  body  ah)no  shouin}.^  at  the  surface. 

Till'  body  in  all  species  is  elongatcMl  (Fig.  '27H)  and  soini'- 
what  riatttsniMl  I'roni  side  to  side,  and  bears  along  the  mid- 
dorsal  line  an  unpaired  tin,  formed  as  a  fold  of  the  boily  wall, 
and  containing  a  cavity  traversed  by  niinKn-ouH  skeltjtal  rmls 
(see  rig.  271))  whicli  serve  as  a  support  for  the  tin.  I'li^ti- 
riorly  it  bccomos  somewhtit  higher,  and  forms  a  caudal  I'm 
surnMUiding  the  postei'ior  end  of  tiie  body,  wliih^  on  llio  neu- 
tral surface  two  tins  run  forward  a  short  distanc(»,  both  U\r^^' 
and  the  caudal  tin  being  supported  by  Hn-rays.  Some  dis- 
tance from  the  hind  end  of  th(>  body  on  the;  left  side  id'  tin' 
cauihil  tin  is  situated  the  anal  optnung  (Fig.  278,  <i),  whil*    in 


i,  j4nij>hi- 

1  lial»it;it, 

suiid,  flic 

0. 

11(1    SdllH'- 

tlie  iiiid- 

oilv  w.ill, 

[.'till   i'»l.^ 

.         Vn^U: 

niil.il   I'm 

till'  \(ii- 

itll    tiM'-^<' 

<lll|i'    'll>- 

U'   .il     til- 

TYPE  PItOTOCUOlWATA.  gQ^ 

(4J.     The  oltVwa ).     f   tli^':  ".r""^'  '^'■"'"'  "'«  ""■"- 

.Mes  of  the  boa;'t .1 ""  e ''e",  ■^^.r  fl,  '"'t •  l"'  "'^ 
crea.„,K  i.  «,e,  f„«e  t„«ether  beW  ete  ':;  t  \  '"^ 
l».-e  thus  e.ch,«i,.g  the  utrial  c.vit/a,  .'^w  ,,,;;,  n"-'' 
hue,l  thr.,„(.ho„t  by  ectoderm  aud  sur  ■om.d;    'l  '? 

veutiHl  surface  of  the  auterior  two  thirds  '■"      '^  "'"' 

liorly  the  cavity  is  ch,spd  l,v  .1    V  ,    ""  ^'"''^'-     '^"'«- 


rt«  r:  eye  "*  =  "•"'*<lo.s. 

*  =  H'trial  c.lmn.l,or.  "  "^  >'c.|,lni,Iiun.. 

ch  =  n,.t„d.or,|.  '^  "^  ""•""'• 

i' =  rc-producdvc.  organ.  i>  -  "inal  pore. 

/  =  liver.  ''"'■'•'''  '"''vc'-conl. 

«i'  -  biniicliial  cltft. 

torn  of  which  Ii.»  th.  oriKii.al  n.onth,  th a.-ins  „f  th„  l,n    , 

i'niso.Iint,,nuMUM-onss.n.so,vpa,;ilIa>.  '   "^'■^"^** 

T  iie  cctodenu  is  vcrv  simnio  in  ;♦  ,    i 

««;;.;^  i..r  of  c„n.;c:;:,i^;;;,:r;  ::•::;;— ^^^^^ 

;:":r::^b;::;:';;:r:;:;:r""'''r^^'"-^ 
-'■■"^''"M.Had.vc;,i,c.i::t:::t:;;:i.:^::;;::;r-;'-;:--;: 


610 


INVERTEBRA TE  M0RPH0L06  T. 


time  these  folds  are  gradually  constricted  off  from  the  intes- 
tine, and  at  the  same  time  are  divided  transversely  into  a 
number  of  sacs  lying  one  behind  the  other,  their  number  in- 
creasing as  the  folds  are  separated  from  before  backwards 
from   the  intestine,  until  in  A.  lanceolatm  there   may  be  as 
many  as  sixty-one.     TLese  sacs  are  the  primitive  mesodermic 
somites,  and  the  cavities  they  contain  are  the  primitive  ca»- 
lomic  cavities.     At  first  entirely  dorsal  in  position,  the  various 
sacs  later  on  extend  ventrally,  those  of  opposite  sides  meeting 
below  the  intestine  ;  and  still  later  the  cavities  of  these  ven- 
tral extensions  fuse  to  form  a  continuous  cuelom  extending  the 
entire  length  of  the  body  on  the  ventral  surface,  and  forming 
what  is  termetl  the  splanchuoccel.     This  becomes  eventually 
separated  by  a  layer  of  connective  tissue  from  the  more  dor- 
sal  portions  of  the  somites,  which  remain  distinct  from  each 
other  throughout  life  and  are  termed  the  myocoels.    The  future 
history  of  the  two  portions  of  the  mesoderm  thus    formed 
is   very  different.     The   walls    of   the   si)lanchnocc)el   remain 
thin,   and  the  cavity  well  marked  (Fig.  279,  co),  but  in   tlit* 
myoccels  the  cells  forming  the  median  walls  become  converted 
into  longitudinal  muscle-tibres  {m)  which  traverse  the  entire 
length  of  each  myocoel,  filling  it  almost  completely,  and  are 
inserted  into  plates  of  connective   tissue  which  develop  be- 
tween the  various  mjoceels  and  separate  them  from  one  an- 
other.    At  the  same  time  each  mjocad  becomes  bent,  so  that 
its  dorsal  portion  is  directed  downwards  ami    forwards  ami 
its  ventral  portion  downwards  and  backwards,  each   muscle- 
plate  having  in  a  longitudinal  s(!ction  of  tlie  body  a  <-shiipL'd 
appearance  and   fitting  into  the  one  in   front  of  it.     AViien 
the   epipleural    fohls    develop,  both    the    s})lanchnoc(t'l  ami 
the  muscle-plates  are  continued  into  them,  the  muscle-])lat{'s 
lying  to  the  outer  side  of  the  sphinchnociel,  and  their  tihrcs 
here    having    for    the    most   part  a  transverse  direction,  in- 
stead   of   a   longitudinal    one,    as    in    their    upper    portions. 
Owing  to  the  myociels  being   practically  obliterated  h\  tlif 
miiscie-])lates,  the  (-(elom  of  the  adult  is  j)rincii)ally  formcil 
of  the  splanchnoc(t'l,  but  other  spaces  also  occur  which  an; 
]n'()ljably   schizocd'lic   in    origin   and   form   various    lacnuM' 
throuL'hout  the  body. 


a 
b 
c 

CO  : 

e  : 


TYPE  PIWTOCHOBDATA, 


611 

ia  wLich  floM  numerous  coTn.T    ""'"'""'I'S  »  ""'"'ess  blood 
Byseem    eo.»i.ts   o    r  11,  rH""''?  ""P"-'--     The 

.-.  po..o„  o.  u.  oo„:::Lnjs,a  r  £r  - 


l^IG,     279.— TnAN8VEH8E     SppTrnw    m„^ 

•lesccndhiff  aoi-hi  ^' '""  "«"twio). 


«  =  (lesct'tiding  aorta. 

*  =  atrial  clmiiiher. 

c  =  riotochord. 
oo  n  co'lorn. 

«  =  liyp<)l)n»Khfnl  groove  beneath 
wliich  is  the  n.scci.ding  aorta. 
9  —  reproductive  orgim 


kb  =  branchial  arches 
^  ~  pharynx. 

I  =  liver, 
w  =  Miiisrlca. 
n  =  nepliridiiim, 
r  =  nerve-cord. 
*»  =  nerves. 


li.e  bmudnul  resiou  „f  tl,e  intestine     It  ,.,,,1.  „ff  i 
va.-.o„s  reKious  „f  the  h„,ly   whid,    ,*,!!'""'''"''" 
f^'I.ilhu-ies,  unite  ,.„„in  to  fi,!  ,l                  '"■""'<'"K  up  into 
V"i".  which,  „u»si„;      „  :.,I  '«""•""-.'-. ■■  vonfal 

«."uehi,;r.--:/r^!e'i^r:L":s^:r:::!: 


612 


INVERTEBRATE  MORPHOLOGY. 


W 


sally  to  unite  witli  the  right  aortic  vessel.  The  blootl  which 
passes  from  the  dorsal  aorta  to  the  iutestiue  is  not,  howevei-, 
returued  directly  to  the  ventral  vein,  but  the  intestinal  capil- 
laries unite  to  form  a  vena  porta  which  passes  to  the  liver 
and  there  breaks  up  into  a  second  set  of  capillaries,  these 
finally  emptying  through  the  hepatic  vein  into  the  ventral 
vessel.  An  hepatic  portal  system,  resembling  that  found  in  the 
Yertebrata,  thus  occurs  in  Amphioxm.  While  passing  be- 
neath the  branchial  region  of  the  intestine  the  ventral  vein 
gives  off  paired  vessels,  the  branchial  arteries,  opposite  each 
branchial  septum,  and  these  passing  dorsalwards  in  the  sep- 
tum open  into  the  dorsal  aortic  trunks.  There  is  no  definite 
heart,  but  certain  of  the  vessels,  notably  the  vena  porta  and 
branchial  arteries,  seem  to  be  contractile. 

The  notochord  (Figs.  278,  ch,  and  279,  c)  has  a  much  more 
extensive  development  than  in  the  Hemichorda,  since  it 
traverses  the  entire  length  of  the  body.  It  arises  from  the 
dorsal  surface  of  the  digestive  tract,  but  early  loses  all  con- 
nection with  the  intestine ;  and  though  in  early  stages  it  con- 
tains traces  of  a  lumen,  this  cpiickly  disappears,  the  cells 
becoming  richly  vacuolated,  so  that  the  notochordal  tissue 
assumes  a  characteristic  appearance.  At  either  end  it  is 
pointed,  and  throughout  its  entire  length  it  is  surrounded  by 
a  sheath  of  dense  connective  tissue,  which  is  continuous 
below  with  the  partitions  separating  the  splanchnoctel  from 
the  muscle-plates  and  these  from  one  another.  From  each 
side  of  the  dorsal  surface  of  the  sheath  a  longitudinal  lamella 
extends  dorsally,  the  two  lamelhe  enclosing  the  central 
nervous  system  and  being  continued  above  it  as  a  strong 
neural  ridge  (Fig.  27',)). 

As  has  been  already  stated,  the  adult  month  is  formed  by 
the  margins  of  the  oral  hood,  the  original  larval  mouth  lyini; 
at  the  bottom  of  the  f)ral  cavity  enclosed  by  the  hood  and 
beiu'f  surrounded  by  a  (drcular  fold  of  tissue  termed  tho 
velum.  A  short  tube  leads  from  the  mouth  to  the  branchial 
or  pharyr.geal  region  of  the  digestive  tract,  whose  walls  me 
here  perforated  by  numerous  slits  (Fig.  278.  up)  ])lacing  its 
<«avitv  in  conuiiuiucation  with  the  atrium  (see  Fig,  270).  In 
the  adult  the  slits  are  elongated  ami  are  i)lac»nl  (iblicjuely  to 


TYPE  PliOTOCIIOHDATA. 


613 

the  brauchial  re^.ion  of  IITZT  '  "^"^^'^eplates  of 

tious  between  each  pair  of  slits  ,;^"^^^^"'^^^'     ^^^  ^Jie  parti- 
tl^e  same  side  of  tlxe  body  skeletal 

|<Hlsoecur  which  unite  above  with  a 

o"gi  udi.al  bar  Ui^^  ,,)ove  the 
<lorsal  ends  of  the  slits  (Fi^.  280) 
A  closer  examination  shows  that 
'Alternate  bars  ditfer  in  structure,  a 
condition  due  to  the  fact  that  each 
I'HU-  of  slits  is  priniarilv  derived 
i'.-m    a    single    slit,  which  becomes 

nuled  longitudinally  by  the  ^.rowth 

T  ^*^•^.7'^' ^^^«-'f  -  ton^uelike 

■live,  which  eventually  fuses  with 
the  ventral  edo-o  of  the  slit.  The 
coadition  of  affairs  then  is  ahnost 
I'lentical  with  what  obtains  in   ^o- 

,"7tTr  ''"^^'  ''''  "^  *'^'^^  ^"i-'".  the 
Nl^eletal  bars  are  to  l,e  conshleivd  as 

Kroupedtoj^ether  in  threes,  although  "        -• 

^'-<^«  '-in«  thus  pro.^^     T ho'  '"•  "'"'^  "'  ''"  ^'^^'^'^^ 

--^"^thebrauciL  l::^eioni  ;:t:rr'^ ""  r^^^^^^ 

l.y  comparing  Fig.  280  .ith  Fi.  27(!' p!  ii)!;;     "  ""^'  '^  ^^^" 
It   follows  from   tin's   flnf   < , 

'■""---.n  of  ,1..  s„, ;  r,      ; , '"  7"'  T'"  ^'^  -''-'i-  n,o 

"-  •''"•■>■  «tu,n..s  of  d..v,.|o,HM,.        :.     ;  i"    ""■;   '"  ""•  "■"-'•-Pl.-.t.s.     In 
■••'-I>"'Hl  .m.ta,,u.rin.ll  \  ^    ,    "    "''^''^■^  '"•*'  ''"-'"i-'i  "Lich  do 

^--•<'  H^  <'.o  ...no , s.  J  *;;;;; "" "''""'  '"'"^  -••■  •-'-! 

,„       ,  "K'ifimon.!  coiT(.spoii,i,.,,e,«  is  lost. 


Fin.   280.-nrAo„AM  ok  tiir 
BiiANdriAi,   Wkki.kton    of 

^»ip^'ioxilS  (after  Si-KvaEL). 
*  -«Vniipliculii. 
«*  -  sf|t;,il  bar. 
<6  =  tongue  bur. 


ive 


ciliate 
tlirou 


i»Joo(J-vesselH  occm-  l.,>fi.   ;     n 

into  ti,.;  ■■;■,"*""''■>■  "'•"■"">'iM««»e8 


614 


IN  VERTEBRA  TE  MOliPUOLOQ  Y. 


exterior  by  the  atrial  pore.  Along  the  dorsal  and  ventral 
mid-lines  of  the  branchial  region  is  a  distinct  ciliated  groove, 
the  ventral  one  having  projecting  from  its  floor  a  longitudinal 
ridge,  while  ventral  to  it  is  a  chitinous  skeletal  plate  composed 
of  paired  moieties  having  a  metameric  arrangement.  This 
ventral  or  hypopharyngeal  groove  (Fig.  279.  e)  is  termed  the 
endostyle,  and  from  its  anterior  end  a  band  of  ciliated  cells 
passes  dorsally  on  each  lateral  wall  of  the  pharynx  to  unite 
dorsally  with  the  epithelium  of  the  dorsal  or  hyperpharyngeal 

groove. 

From  the  digestive  tract  behind  the  branchial  region  a 
diverticulum,  termed  the  liver  (Fig.  278,  I)  arises,  and  pro- 
jects forwards,  covered  of  course  by  the  body-wall,  into  the 
atrial  cavity  (Fig.  279,  I),  and  behind  this  the  intestine  passes 
straight  back  to  open  at  the  anus  (Fig.  278,  a),  situated,  as 
already  indicated,  upon  the  left  side  of  the  body,  some  dis- 
tance from  the  posterior  end. 

The  nervous  system  consists  of  a  thick-walled  tube  (Figs. 
278,  and  279,  r)  which  lies  immediately  above  the  notochord 
and  is  enclosed  by  the  connective  tissue  lamellre  which  arise 
from  the  notochord-sheath.  It  extends  throughout  the  entire 
length  of  the  body,  tapering  rather  suddenly  at  either  ex- 
tremity.    Throughout  the  greater  part  of  its  course  the  lumeu 


Fig.  281.— Diagram  of  the  Antekior  Portion  of  the  Nervous  System 

OK  Amphioxiia  (after  Hatschkk). 

cA  =  uotochord.  JV  =  hypophysis. 

1,  3,  3  =  are  placed  over  the  three  ventricles. 

is  very  small,  forming  the  central  canal  from  which  a  well- 
marked  cleft,  the  dorsal  fissure,  extends  to  the  dorsal  surface. 
At  the  anterior  end  of  the  tube,  however,  the  lumen  ealar-os 
to  form  an  anterior  ventricle  (Fig.  281,  1)  which  has  been 
compared  with  the  anterior  of  the  three  primary  vesicles  nf 
the  Vertebrate  brain,  and  behind  this   the  lumen  couUucts 


rYPS  PBOrOCHOHDATA. 


VOD9  Stbtesi 


615 

formiug  the  aqueduct  of  Svlvins  nf  n,=      • ,  i     • 
belaud  this  again  au  expaudon  !f  fh    1       ^  '"''""  ^^^^  "''"« 
do«ul  fissure  form,  a  /C T    /  .'?1  .'''"■"'''  I«"«°"  of  the 
the  Vertebrate  hiuTbrfr  the  ,  n"  ^'^  '""""  *°  "'»'  "' 

Vertebrate  braiu  I^TCI  :;t':rir,*°  "'"  ^"'^-•^•"-<' 
which  is  increased  bv  tl,„  ^  umrked— a  resemblance 

(^)  of  the  :S  ten  r  e^r^'r  ?/  "  '""'""-"''''  -'--on 
l^od,,  where  it  ZT^^Z^^'^  ''«-'  ^f-  of  the 
Jerm.     This  is  tiie  rem  J,„  nf  JeP'-essiou  of  the  ecto- 

-itl.  t.,e  oxter"";  rh  e,ftsrtT"'"f  °''  °'  "-^^-'Wele 

-verare";:rffrc28i)  trrr ''--  "^'^-  °' 

come  from  the  dors- 1  nm-t;  „      ,  '""'  ""°'"'  of  wldch 

1-i.-  on  each  sll       "  ,,  X  ™  "  '^™"'  ^''""^  ""^  "-"J 

tl.e  dorsal  surfa  e  of  e  b,'.! n"'?"''  '!  "  '•"<"  ■■"'"■''«  '-"' 
v-tral  side,  a  condi  i  :,',  J  "  iT;'  r.lfr '  "  m""«  '"'"•  "- 
...etamerically-arranged  nerv  T,  ,"' ,'"  '  "  ^-'eJing 
■■ever  unite  to  form  a  comm™,  ...  """'  ™''"''''  "-oots 

'-0  the  .^.-inerve:r. :,  ;::trb;;t  r^tfr*'"'''''^ 

are  sensory  iu  fauctiou,  while    he  1 IV^     •"=^'='-"»Iess  they 
-.W;binK  only  the  mus^lature  t^  tCbol"""  ""  "'°'"^' 

I"  addition  to^hese  a;\>:  .l'\:''';''''-^'"  '•-«»'• 

ai.  exceedingly  simple  evl  Z       ^     '       ""''  '""^  »-ei>rosent 

'l.e  brain,  am/in "^  '  .S^'.f     r„,::'r:  t  -"""""^  ""'  "' 

;>■■«-,  -..-rounding  a  depr  ss    „     irS."  ''f  ^■''  "'  -"^ 

«a„ng  l„„g  refractive  hiirs.     Tl,       1        j:''"""''""-  ™"» 

0  a  sense-organ  of  some  kind,  but  its  exlct  f      !• """'"'  '" 
ku(nvn.  ^  ^^^c*  function  is  ujj. 

Differeut  stiiicture.s  Iuivp  fmm    r 
*lered   excretory  organ        I„  2   «"!   '?  """'  ''«°"  «™- 
'•-«"..  l.a»  been  assi'I^^  J'l   "^^^    .•"7.  -  ---tory 

of  the  oral  cavity  on  'tl.e^  fcft's  d  '':,'     !'"  ""^' '"  "'"  """ 

siiK,  and  conimumcating  by  u 


616 


INVERTEBliA TE  MOliPIIOLOG  Y. 


fuunel  with  the  coelom  just  behind  the  level  of  the  velum. 
{Secondly,  although  iu  all  probability  they  are  not  uephridia, 
the  "browu  cauals"  may  be  here  meutioued.  These  lie  in 
the  sphiuchnocuel  at  about  the  level  of  the  twenty-seveutli 
muscle-plate  in  A.  lanceolatus,  and  open  by  wide  funnels  into 
the  atrium,  though  it  is  uncertain  whether  the  inner  end  lying 
in   the  coelom   is   perforated.     Thirdly,   iu   the   pharyngeal 


I      n   s    r       11 

Fig.  283.— Excuetoky  Organ  of  Amphioxus  (after  Bovkri). 
nc  =  uephrldium.  tip  =  uephridiiil  pore. 

nd  =  nephridial  fuiuu'ls.  «  =  synapticiilum. 

/  =  braucbial  septum.  //=  bniuohial  tongue. 

region  a  number  of  nephridial  canals  have  lately  been  de- 
scribed.    They   are  situated   above   the   upper   ends    of   the 
branchial  slits  (Fig.  282,  nc),  each  opening  into  the  atriuiu 
()pi)OHite  a  tongue-valve  {np),  and  from  the  short  tube  whuli 
passes  inward  from  this  opening  an  anterior  and  a  posterior 
l)ranch  arises,  each  of  which  opens  into  the  coelomic  cavity 
by  a  terminal  funnel.     Between  these  two  funnels  three  or 
four  others  may  occur  (nd),  and  around  the   mouth  of  eiu:h 
funnel  are  a  number  of  threadlike  jn-ocesse  i  which  end  iu 
round  strongly-refractive   cells.     That    these   structures  are 
UPDhridia  seems  indicated  by  their  relations  to  the   cwhm 
and  furthermore  by  the  fact  that  iu  the  neighborhood  of  eacii 


TTn  PBOTOCHOBDATA. 


of  tLem  the  brancliial  blood-vessels  fr,,™  „    , 

may  be  regarded  as  a  glomeru  ussuH     "  ""    '  P'"''™  ""«'' 

t."-vith  the  uriuary  ttbulerol"  .rVertlrrtru,  "  """"^"^ 

Ampho^,^  is  bisexnal.     The  nmZZt  ^^• 

or  testes  (Figs.  278  ami  279,  M  occH    iu  the  '  °T" ''  "''""'' 
"UJ  are  arranged  metau.o  i.,!!         /  epipleural  folds, 

Tl.ey  lie  at  the  level  oi  the  ^f  T  ""'■':>'->'i^"'  metamere. 
=-1  the  ventral  trins  Lt  , C!  e"  ,"'  '"'"•"'  '""^itudinal 
«  cceiomic  cavity  wh  •  h  L  lit'  ""f  7'  """'"'"'d  ''"''in 
of  the  segment!  o  '  •  i  h  tiL'"'  1  ""  °"«'''^'  "^o^^'^ 
Tl^ey  lie  on  the  inJ^^'t^^T^'^-^Zr  ''^ 
covered  ou  their  iuuer  surf-.PP«  1     li     !,  ^°^'^'''  ^^^  a^'e 

-i-1^  the  rern^oan    C  ;^^^^^^^^^^ 

;^to  the  atriun.  and   thence  1    iullo  I^  "  T'""'  '^"^"^' 
the  atrial  pore      Thpvp  ..v        *'^^^'"^^^  *«  the  exterior  through 
poie.     iLeie  are  no  reproductive  ducts. 

considered  the  mos;,,n„-uX^^^^  ^'--  -»all>  been 

•"  =^  'nore  or  less  modified  condi  on  ,p\7  7^^^«"^'"g.  ^"  other  words, 
i-e  deseended,-and  there  a  em?'  "^  :'"/':«'"  ^^'^'^'^  the  Vertebrata 
o~^'ns  and  the  larval  L'Mnm-J.rZUTl^'T^^^^^^^ 
-I'Ported.  The  character  If  ::r:f  t',!  'f  ?"''  ^^  ^'^•^^'  ^^^  '- 
«V«tem,  the  arrangement  of  the  ne  X  nP  .  ,  ""'"'^^"'•'^  '"^"^  "^^'vous 
If  ^tes,  the  occurrence  of  an  h  pit  ,o  ,.  i  ',  'T'^  *'"  '''''^'  "^"^de. 
f''«  early  stages  of  devel,>pme  t   'rf  ^  i    '''7^'^^'""  '-^"^1  the  character  of 

-Plioable  only  on  the  snpp     u^.  o'a'son  "v.    .  '    "'"""''^^  ^^'^"^'^  «««'" 
Ou  the  otiier  hand   ni  i.,..  .   '^o^'e^'Iiat  close  affinity. 

,  '-  -r.ed.  It  trlr  '™  ^  ;  e  Enteropneusta  ar^  hut  slightly 
the  arrangement  of  the  ^^r..^T^J^J^^'^r  ^^""'"•'^'-  ^^ 
<'^'Pen<lently  in  the  two  forms,  and  the  "t  -i  J    'T.  '"'"  "'^""'^^  "^- 

I  -■;,.^•u•ded  as  the  more  extensi  oly-dev  1  k  It  Vl  /r"'^"'''^  '"'-^-^  »^« 
•  "VV..>..,,.  is  nndonhtediv  much  more      1  .       '  ''^  ''^"''"">.'^^»*v"*-- 

,  !''au  yy./„.o,//..v.,,  ,,Kl  both  are  1 ;  Iv  '  "'"'  '''^  ^^"'^^'''^■"^•^  ""« 
;--  ^'-  <ii.-t  line,  but  the  gou".^  ^'^  i";"*^  '\  '^^  -'^^'^  <li  v-^ent 
•'--  ial  slits,  of  an  endod;rnu^^^  „^^  .  f^^ 

'■'■"^'•■'"  nervous  system,  which  have  led  ^o.''        .      ''  '''''•^'^"y-place.i 
'""■  typo  Protochonlata,  spe.k  stronelv  Jor       •'•"'^'^'''■'^'«»  "^  ^oth  forms  in 
,     '^.e  principal  difficulty  in  t  ie  Zv  of     .    "'""'""''  "'  "'-"^'^"*- 
h  the  representative  of  the  anc  st  ,    f,       '7'"'"'""  ^^^  ^'^^^^^^.'/fo.v... 


618 


INVERTEBRA  TE  MORPHOLOG  T. 


indications  of  Vertebrate  ancestry  among  the  Annelida.  This  vlifiBculty 
depends  upon  the  interpretation  placed  upon  metameiism  and  the  causes 
assigned  for  its  origin.  If  the  ideas  regarding  these  points  advocated  in 
preceding  pages  (see  pp.  43  and  217)  of  this  book  be  accepted,  the  dilKculty 
seems  to  be  practically  done  away  with,  since  these  ideas  imply  a  possi- 
bility of  the  independent  origin  of  metamerism  in  ditfertut  groups.  And 
indeed  it  has  already  been  pointed  out  that  such  an  independent  origin  lias 
probably  occurred,  the  metamerism  of  the  Annelids  being  probably  entirely 
unconnected  with  the  metamerism  found  in  the  more  highly-organized 
Platyhelminths  (see  p.  217). 

A  full  discussion  of  the  intricate  problem  of  the  origin  of  the  Vertebratu 
would  be  out  of  place  here,  but  one  additioijal  point  may  be  referred  to. 
Difficulties  have  always  stood  in  the  way  of  an  homology  of  the  Vertobnite 
nervous  system  with  that  of  the  Annelids.  In  the  latter  there  is  a  supra- 
oesophageal  cerebrum  and  a  ventral  chain,  while  in  the  former  the  entire 
central  system  is  dorsal  to  the  digestive  tract.  Various  theories  have  been 
advanced  to  account  for  this  difference,  none  of  which  have,  however, 
proved  entirely  satisfactory.  The  acceptance  of  an  ancestry  leading  baeii 
to  Hemichordalike  forms  obviates  this  difficulty,  since  in  these  the  slightly 
differentiated  nervous  cord  is  already  entirely  dorsal,  a  future  extensi.m  of 
it  and  a  metameric  arrangement  of  its  elements  and  branches  in  correla- 
tion with  the  metamerism  of  the  mesoderm  bringing  about  the  Vertebrate 
condition.  Furthermore,  the  occurrence  of  a  central  lumen  in  the  nerve- 
cord  and  the  mode  of  its  origin  are  essentially  t lie  same  in  botli  Verte- 
brates and  Hemichordates,  a  fact  which  in  itself  must  be  given  no  li'.tJe 
weight  in  the  final  determinatirii  of  the  (juestion. 


A: 


III.  Class  TJROCHORbA. 

The  Urocliorda,  also  known  as  the  Tunicata  or  Ascidiuns, 
are,  like  the  other  Protochordates,  exclusively  marine.  At 
first  sight  they  appear  to  have  little  resemblance  to  such  a 
form  as  Amphioxus,  the  majority  of  them  lacking  in  the  adult 
condition  all  trace  of  a  notochord,  though  a  branchial  re;^Miin 
of  the  digestive  tract  is  always  present.  In  a  few  adult  forms 
(Appeudicularians,  Fig.  285),  and  in  the  larvne  of  all,  aAvell-df- 
veloped  uotachord  is  present,  however,  situated  in  abackv.ird 
prolongation  of  the  body,  resembling  in  appearance  and 
structure  the  tail  of  a  young  tadpole — an  arrangement  wliicli 
has  suggested  the  name  applied  to  the  class.  In  the  majority 
of  forms  this  tail  disappears  at  the  close  of  larval  life,  and 
with  it  the  notochord  also  vanishes.  The  name  Tunicate  is 
derived  from   tiie  fact  that  the  body  is  enclosed  within  an 


TYPE  PHOTOGBORDATA.  g^g 

table  cellulose  ciemioal  characters  to  vege- 

may  be  considered  a  tvp[ca    ll^  f      "^'  .'"  '''='''"  ^^1'"' 
<iue«%  the  move  importout  mod^H^?    '  ''T'"'^  °'"  ^"l'^^- 

The  simple  Ascidirsarefotth!  "?''''"''  °'='^"'-- 
aud  usually  attached  at  cue  eLd  o  ,"  ''"'  °"'^  '"  ^°™ 
geuus  ^Wfema,  however  the  Lrf«  /'  '"PP"':  '"  «■« 
extremity  of  aueloiiwated  shit  r,  ''"''^'"'"'"«  «  at  the 
iuto  the  pyriformbtdy  the  tist"  "t  "'  °""''  ^'"'  ^--s 
the  body  presents  usually  towai^s  thi  iT"  1"1'  ^""'"•^'^ 
two  opemugs,  through  oue  ot  "itk  I'lVntI  ""  ''""^ 
water  passes  iuto  the  interior  of  Jhe  l!!l  ."'  "P""'"'"' 
expelled  through  the  seen, ,  .1    ^^'  ""''  '*  eventually 

composed  of  »  mat^  somefi  mL' al     Tf""     ^'''^  '-'  '" 
times  fibrillar  (tV^toTd^f  "  ''omogeneous.  some- 

by  the  ectoderm.  iToitel  '7'"!  """^'^te-cj.  secreted 
cells,  which  have  reL^uXn  :wrn''t'''r«''  "  """''°- 
origin  and  to  migrate  into  the  t.TT  ?  ^  n^esodermal  in 
taiu  thickness.     Thev  mlv  7  ''  "  ''''''  ''"'ched  a  cer. 

develop  vaeuoie,tirg':hrb:roir  '^''r  ■"■  -^ 

structures,  or  may  become  tbl        .     I       "  '"'"  I'ladderlike 
»■■,  finally,  may  secrete  spicut  of'      >     '"^--'-'''Positions, 

Extending  through  0  etelt  a™  ""'"'""'  "*'  """^■ 
'vhich   communicate   .^1    Ihe   Won7"''"7  '^™-'-«  tubes 
They  arise  a.  outgrowths  of  the  bT    r''"'"    °^    ""^    """'y- 
l.od.y.wall  before  fhem    beii    L^  T''"™?^"'^  ""''  P»«>'  "ie 
ectoderm,  beneath  wl  ch  is  Tl.  .'■'  '"""'  «"'™''Hy  by 

each  is  separated  int^    J:  cirr^  eT^r""^^  "^^"^' ""^ 
partition  which  does  not  L        '  ''   ^>'  "  '""si'u.liual 

enlargement  with  .tier;  iThZ', "''"J'  '"*"  "'«  "'»'""- 

:--c_.ati:^n^rb\t\- 

oppoiiiirbiariiiXHSTatr  "'"T  -'■- 
--  out  into  two  '"^uiar  pr„;est:rthe'"c.';i:i'rd'::  •:: 


II 


620 


INVERTEBRATE  MOliPHOLOOT. 


siphons,  in  whose  walls  circular  muscles  are  developed  to 
serve  as  sphincters  of  the  opeuiiigs.  T}ie  branchial  siphon 
opens  posteriorly  into  the  branchial  region  of  the  digestive 


Fig.  283.— Figure  of  a  Tunicate,  ILterotrema,  removed  prom  the  Test 

(after  Fiedler). 
A  =•  atrial  pore.  pc  =  periphiuyugeal  ciliated  band. 

an  =  auiis.  «  =  stomach. 

CG  -  cerebral  ganglion.  m  =  subneural  gland. 

en  —  endostyle.  »i  =  branchial  stigma. 

ex  —  excretory  organs.  t  =  testis. 

/  =  intestine.  iid  =  vas  deferens, 

tract,  the  opening  being  known  as  the  mouth,  and  usually 
being  surrounded  by  a  number  of  tentacles  (Fig.  288)  wliich 
arch  over  it.  The  atrial  siphon,  on  the  other  hand,  does  not 
open  into  the  body  proper  but  into  a  cavity,  lined   probaiily 


TYPE  PROTOCnORDATA.  Qg^ 

anterior  and  posterior  em        TL  '  .  "•"''  f '  "'"  ''""■^■"'^ 

Ws  walls  are  tenued  tl  e taufle  iT- '^' '"  "'"  ""■""■'  ""-1 
atrial  o..ityoiA,npMoJXT^:Jll:°7r'"'  '"  "« 
sive  developueataml  arises  ia  tie  Kvv  ■""'■"  '*'"'"■ 

".en>  at  t,i  sa,„e  t^L'dl't,;    r    ,!  t":;;  t^l" 'r  '"''"''^" 
become  coiitiuuous.  ^'  ^'''^  ^'^'^^  cavities 

The  external  surface   of   botJi  flm  ,»     n 
proper  is  covered  witl.   elde™  tu    ret    ,"",''  ""^  ''°''^- 
layer  of  mesodermal  connective   hsuei'T        f"'"  "'""'  * 
iibres.     The  cu,l„,„ic  cavity  1,^1    of  °7''""*'  """"='''- 

■spaces  which  l.ave,e»pecii„;r,t  ais'of  «'■"  '""'""■ 
'■es-on,  a  more  or  less  cleiinitei.ra.l;e,,  „  ^^^^  .  '«  """"r'""' 
vessels.     In  a  somewhat  ,H«t;,„.t     *'        "'  "'"'  '^"^  as  blood- 

t'.e  bod,  is  situated  at  hi  'tri^ir""'  "T,  '''"'  "'"'  "' 
of  a  single  layer  of  cells.  Z  t^l^"  7"'^.  ?'"  '""'""' 
verted  iuto  muscle-Hbres      Tl,„        .  '  ''''"•"''  "'•«  «'u- 

wavelike,  starting  f™,„^een^a  J  '■"'!™'  "'  '""  ''^•■"■'  -- 
rather  .nieUl,  to;ards  ^21:^^^:^!^'^'  'f""*-"' 
«  that  after  a  certain  number  of  beafs,'/'™'"""^ 
contraction-wave  be..iu,  «„,„„,!'       ""'''  "^  ^'•''''=''  ""> 

andf„rasimihu.n„i:fratnh;:i™r:j 

This  change  takes  place  with  a  certJn  f  ?    "''  '''"'• 

and  at  each  change  The  course  o^  til  7  >  ;',°""'  "'  '■''^"""' 
at  least  of  the  l,ody  is  reve  led  1  7  "■""«''  '■•  l""""" 
;..'"  a  large  lacnua,  one  I  ' ^  Lh  nn  f  ir'n'"'  ''^'"■'  ""-» 
i"e  of  the  branchial  sac,  while  tl't,'^  '«:;:;'?''  ""''■ 
branches  to  the  intestine  niid  t^^t  ,    ^     ^  ""  lacunar 

line  of  the  same  r  giorsmalle.  C'"'  "  °""  """  '''"■^'''  ■■"''-       ■ 
cl.;al   bars,  nuitiug  ^^the"  Zf^^r^^^Z^^"  ''-"■ 
colorless  and  contains  amoeboid  oornnscL    vK  V  '"""'  '" 
usually  coloriess,  though  a  few  coWed  nn  '  "'■"  '•''"" 

pl«mentedeeUsofthe^st,are7:°;::!tr;:;;r"''""«  '"^ 
li-e  mouth  opens  into  a  capacious  pharyngealor  branchial 


622 


INVEliTEBRATE  MORPHOLOOT. 


\ 


l\ 


't 


sac  whose  walls  are,  perforated  by  numerous  slits  or  pores 
termed  stigmata  (Fig.  283,  st),  arrauged  iu  transverse  or  spiral 
rows.      The   bars    separating  the   stigmata   enclose   lacuna) 
which  place  the  ventral  and  dorsal  branchial  lacunre  iu  com- 
munication  so  that  the  walls  of  the  sac  are  richly  supplied 
with  blood,  opportunities  for  its  aeration  being  provided  by 
currents  of  water  drawn  by  the  cilia  which  border  each  stigma 
through  the  mouth  and  out  into  the  atrial  cavity,  whence  it 
escapes  by  the  atrial  aperture.     The  transverse  bars  which 
separate  the  rows  of  stigmata  are  generally  stouter  than  the 
longitudinal  ones,  and  iu  most  species  there  is  a  second  series 
of  longitudinal  bars  lying  on  the  inner  surface  of  the  sac,  less 
numerous  than  the   bars  which  separate  adjacent  stigmata, 
united  with  each  transverse  bar  by  a  short  connecting  branch, 
and   bearing  opposite  each  junction  a  hollow  papilla  which 
projects  into  the  cavity  of  the  branchial  sac.     Running  al()n<r 
the  entire  ventral  mid-line  of  the  sac  is  a  ciliated  groove  (Fig. 
283,  Ev)  bounded  on  eacli  .side  by  a  distinct  longitudinal  ridj,'e. 
This  is  the  endostyle,  comparable  to  that  of  Amphio.vus,  and 
from  its  anterior  end  a  band  of  ciliated  cells  {pc)  passes  dor- 
sally  on  each  side  of  the  pharyngeal  wall  to  unite  in  the  dorsal 
mid-line.     In  front  of  these  bands  another  pair  running  par- 
allel to  them  is    usually  found,   the  two  pairs  forming  the 
peripharyngeal   ciliated    bauds.     From   the  dorsal   point  of 
union  of  the  two  posterior  bauds  a  ridge,  the  dorsal  lamiii;i, 
extends  backwards  in  the  dorsal  mid-line  of  the  branchial  sac, 
and  in  many  species  (Fig.  283)  is  produced  into  a  number  of  pro- 
cesses succeeding  one  another  at  intervals,  and  projecting  into 
th(»  l>rauchial  cavity  ;  these  are  termed  the  dorsal  languets. 

The  remaining  portions  of  the  digestive  tract  is  in  i\w 
«imi)le  Ascidians  generally  situated  iu  the  mantle  on  the  left 
.side  of  tlie  body,  owing  to  the  enormous  development  of  the 
branchial  sac;,  but  iu  other  forms  it  constitutes  a  part  of  a 
viscv^iid  mass  lying  immediately  below  the  posterior  end  of 
the  b"-c.  The  tt3S(jphagus,  l)egiuning  at  tlie  lower  end  of  thii 
sac,  forms  a  short  tube  wliich  opens  into  a  fusiform  stoma.  Ii, 
from  the  further  end  of  which  the  inte.stiue  (/)  arises.  This 
is  generally  bent  twice  upon  itself,  forming  thus  two  loons, 
and  ends  in  a  straight  piece,  the  rectum,  which  opens  by  tho 


TYPE  PROTOCHORDATA.  623 

eutue  length  of  the  muer  surface  of  tlie  iutestiual  wall  form 
HR  the  typhlosole,  aud  a  number  of  brauche.l  tubule  '  open" 

«ud  aud  giving  oir  nerves  both  anteriorly  rnjl^f^T'' 

tbe  anterior  part  of  the  brancSre  '  "tt  Lt  X"  Jet 
,^arkod  papilla  which  n=av  possibly  be  .JoILL:^^ 
rhe  gland,  from  .ts  relation  to  the  nervous  system  and  tT^ 

£:rr"r  .:;„i:rr,'  rtSif  r-ss 

orsal  languets,  and  the  papilla  at  the  opening  of  the tl  ^ 
the  subneural  j<laud.  ^^  ^'  "^ 

Au  excretory  fuuction  has  been  asmVi.^.l  +«  +i  i 

«laud,  but  in  addition  to  this  theTe  arl'T  'ud°if  ehTvt::: 
mass  a  number  of  spherical  bodies  (.,r)  without  du-tsi! 
whose  cells  concretions  of  uric  acid  are  fould  The  "e  seem 
to  ropreson  excretory  organs,  the  waste  material  LteaT 
bowever,  ol  being  passed  out  from  the  b,„lv  IV      ,  ' 

the  cejls  of  the  organs_a  conditi.:  recaKlat ttu:.',  I 
some  Echlnodenus  aud,  to  a  certain  evtent  fZ 
iu  the  Ectoproctous  Poly.oa.  '  "'"  "'''■'"'S'^"'™' 

The  Tuuicates  are  tor  the  most  part  hermaphrodites     Tl,„ 

-^viductiscontinuorrr':,:-:;;'!;;-:::-:: 

the  atiial  cavity,  .,pomiij,'  into  it  in  close  i)rovi„iK.  f 
HUUH.     The  testes  rFi.r  9«q  /x    ,  pioMiiuty  to    the 

xiit.  icsics  (1  ig.  j«j,  /)  ftre  munerous  spherical  l)n,li«w 

-* 'r  miJXI     jt/il'«     i.-ti-ii  .»i 1  r- 


inn  mm  utiierH  to  form  tJie  siijgl 


e  vas 


624 


INVERTEBRATE  MORPHOLOGY. 


-91 


deferens  {vd),  opening  into  the  atrial  cavity  near  the  opening 
of  the  oviduct. 

On  account  of  the  larval  characters  being  more  important 

than  the  adult  in  indicating  the 
affinities  of  the  Tuuicates  and  in 
justifying  the  term  Urochorda  applied 
to  the  class,  it  seems  convenient  to 
depart  froir  the  usual  arrangement 
and  consider  the  development  of  tlie 
simple  Ascidians  here,  before  passing 
on  to  a  description  of  the  various 
orders. 

Development  of  the  Simple  Asci- 
dians.— For  an  account  of  the  early 
development  reference  must  be  made 
to  embryological  texf-books,  the 
present  description  being  confined  to 
the  larva  and  the  changes  it  under- 
goes in  transforming  to  tl'e  adult. 
Suffice  it  to  say  that  the  early  stagos 
resemble  very  closely  those  of  ^\iii- 
phio.nis,  and  they  result  in  the  fornia- 
Fio.  284.— DiAOHAM  OF  THE  tiou  of  a  remarkable  structure  usually 
Taupoi.k    Lauva    of    a    known    as    the   Ascidian    tadpole,   a 

term  which  indicates  its  general  aj)- 
pearance.  This  larva  is  a  free-swim- 
ming organism  and  consists  (l"'ig. 
284)  of  an  anterior  somewhat  globular 
])()rtion,  the  body,  and  a  ])ost<'riiii' 
tiattened  region,  the  tail.  TluuMitiic 
body  is  enclosed  within  a  continuous 
case,  the  test  yc),  which,  in  tin-  tail 
region,  is  elevated  into  a  dorsal  ami 
ventral  ridgt>,  serving  as  fins.  Tjinh 
the  anteri<u'  end  of  the  body  ait- 
l)apilhr  (np)  which  serve  for  fixation 
wluMi  the  larval  life  is  coniplett3d,  while  in  the  interior  "f 
the  body  region  imlications  of  tlie  various  adult  organs 
may   bo   seen.     Certain    interesting    modiiicatious   of  these 


Tunicate. 

a  —  iihUH. 
iio  =  atrial  orifice. 
ap  =  adlicsive  pajdlla. 
at  =  atrial  ciivity. 

6  =  cellulose  test. 
ce  —  brain. 
c»  =  endostyle. 

h  —  heart. 
m  ~  inoutli. 

n  =  nerve 
ne  —  iiolochord. 
ph  =  pharynx. 
$g  =  Hiibnoiiral  gland. 


TYPE  PROTOCHORDATA.  625 

are    however    to  be   noticed;   the  atrial  cavity   (at)   is   vef 
quite  small  aud  tlip  fiiin«  (n\  ^  ^-o-vitj-    \^ai)   la  yet 

with  if,  while  the  ITtI,/  ^  ?\  "'"y  '"'*  <=o»>"umcate 

.«-t  .e.t.kable  ^'^^ ^tJ^ ZIZJTT  "  ''^ 

:-:rtL:  zt:^s^z  :!,;t;r  ^-"r 

J-Ces  of  ,vMeh  it  «e.„«  „n  .en-l^la   .  ::.'  ^ 

tube  throughont  nearly  it,  entire  ieugth,  lie,  a  uotochoil   1 
wlwch  servex  a,  a  skeletal  support  to  the  tail,  au    o"  ii" 
«.le  of  ,t  «  a  plate  of  lougituib-ual  .m.sde-fibres 

iiy  uioauH  of  energetic  lateral  movements  of  the  tail  this 
arva  s,v,,ns  about  for  s,„„e  tin,e,  but  when  about  to  tra' 

one';,;;;  >;■'" '"'"" " '''"'"■" '- -•- -""io 41 "; 

me  ol  the  a,lhes,ve  papilla,.     The  tail  with  its  nervous  svT 

t"n,    n,„scles,  a„<l  notoohor,!    then  „n,lergoes  deg       ratin 

an,l  .s  eon,pletely  absorbe.1,  the  portion  of'tl.e  test  «  ™r Z 

-  UR  thrown  oft;  „n,l  a  rotation  „f  ,l,e  I,,,.!,-  takes  pla'    "' 

at  the  nuMUn  eon.es  to  lie  at  the  opposite  en.l  of  the  bo,  y 

".u  the  po„,t  of  fixation.     The  branchial  an,I  atrial  .:^. 

tu.cs   forn,,   ami   the   anterior  saclike   brain   collapses    the 

-nse-organs  dcgenorat,.,  an,l  the  a.lult  brain  is  gm,  I,., 

''"";'"l;'"';,'^'"'  "''•"^' f  '1'"  ■■'t.iun,  ,„„1   tn,   1         , 

-n    o  a,I.l,tn,na    stignnaa  con,plete  the  ac.nisition  ,  f      e 
itdult  oluiracteriHticH. 

It  will  be  seen  from  this,  then,  that  the  larv,e  are  of  great 
inportanco  ,n  estnnating  the  systen.atic   j.osition   an,l    the 


Appendiculariiv,  in  which  tli,>  tail  and 


i!h1  tjjut  tlie  ndiiltH,  except  in  tl 


the  fi 


!lH 


■eo-Hwiimning  Iwihit 


626 


INVERTEBRATE  MORPHOLOGY. 


Several 


are  persistent,  are  to  be  regarded  as  degenerate, 
orders  of  Tuuicates  may  be  recogoized. 

1,  Order  Larvacea. 

To  this  order  belongs  the  genus  Appendictdaria  which  has 
already  been  several  times  mentioned.  It  is  throughout  life 
free-swimming  and  retains  the  larval  tail,  greatly  resembling 
in  general  appearance  a  tadpole  larva.  It  secretes  an  exten- 
sive test  which  is  gelatinous  in  consistency  and  is  but  loosely 
attached  to  the  body,  being  frequently  thrown  off  shortly 
after  its  formation.    The   body  (Fig.  285)  is   comparatively 


f 


.Fig.   285.— An   Appendicularian,    Oikopleura   cophocerca   (after  Fol  from 

Hrrtwio). 
a  "  unus.  /=  ciliiited  groove. 

c  =  uotocbord.  (f  =  brain  with  auditory  vesicle. 

d'  =  pharyux.  g'  =  first  guiigliou  of  tall, 

d"  =  stoiiwich.  /i  =  testis. 

en  —  eiidoslyle.  ov  =  ovary. 

«  —  brauchial  cleft. 

«mall,  the  tail  being  attached  to  its  ventral  surface,  while  its 
posterior  extremity  is  somewhat  enlarged  and  contains  th«^ 
reproductive  organs  {ov  and  h).  The  branchial  sac  has  but  a 
single  pair  of  stigmata  («)  which  open  to  the  exterior  b)  a 
pair  of  funnel-like  tubes  situated  behind  the  anus.  This  ar- 
rangement represents  exactly  a  condition  present  in  the  larvio 
of  other  Tunicates,  two  stigmata  lirst  forming  and  the  atrial 
sac  arising  as   two  separate  invaginations  of  the  body-wall 

J  —  -A-  —    — l.r-.l.     Al-a.    •»*.».*»..»•»»    <.iw».v.  <^i.«    ^^*\r\*%      4-l»/^    1  tiiraryi  1)  <   f  loTlu    rvtilv 


Several 


rhicli  has 
;»liout  life 
isembling 
au  exteu- 
it  loosely 
tf  shortly 
jaratively 


ter    Fol  from 


esicle. 


,  while  its 

itaius  tlu^ 

has  but  !i 

erior  b)  a 

This  ar- 

the  larvio 

the  atriiil 

body-wall 

-tions  nulv 


TYPE  PROTOCUORBATA.  627 

later  fusing  to  form  the  extensive  atrium.     The  eudostvle  ie.\ 

(cWipts  ht.lo«  *i  1  ,  h'^^h^i'i  IJ/ ;•     llie  uotochord 

2.  Order  Ascidiaceae. 

iiiey  ditter  from  the  Larvaceje  cliipflv  ,■„  +i        i         J°"-^«". 

tail  iu  the  acIuU  aud  iu  the  at^e  d  ve/„,  l^t  oft," ','"  "V't 

sac  aud  the  m„ue.-„„«  stif-matt  '"'"'"P""^"' "^  "'«  '"''■"^""al 

Ow,n„  to  the  complexities  prclueed  by  the  methods  of 

InuUms  .t  ,s  cstoma..,  to  divide  the  o..de/i„to  ..boSate 

1.  Suboriler  Aaeiilm  simplkes. 
Tl,e  simple  Aseidians  agree  with  the  description  civeu  a, 
typ.oal  and  ,„  not  re.p.ire  any  further  notice  llr,    eSe.t  Z 
moufou  the  fact  t  u.t  there  are  included  within  t!,.:  suIk^'i 

innpima.     1  ^  formation  of  new  individ.mls  takes  „l,„-e  i„ 
these  cases  from  stnlonlike  oiitirrowths  of  the  nnl.  , 
uud  each  bnd  remains  seated  upo'n  tl  " ttln     „  4      1  d',',"; 
ts  own  test.     The  stolon  (Fi,,.  28r.)  arises  fron,  the  lower  'f 
->n  of  u.e  body  of  the  parent  and  pushes  before'  it  a  por  i    i 


628 


INVERTEBRATE  MORPHOLOGY. 


of  the  test ;  the  cavity  it  contains  is  continuous  with  the  body- 
coelom  and  is  therefore  lined  b}'  mesoderm,  and  is  divided 

into  two  compartments  by  a  longitudinal 
partition  which  may  be  traced  back  to 
its  origin  from  the  posterior  wall  of  the 
branchial  sac  of  the  original  individual. 
Since  ectodermal  tissue  lies  between  the 
mesoderm  and  the  inner  surface  of  the 
test,  the  stolon  contains  portions  of  all 
three  germ-layers,  and  a  portion  of  each 
jjasses  into  each  bud  (b)  as  it  arises. 
The  first  indication  of  a  bud  is  a  slight 
wartlike  elovatio'i  of  the  wall  of  the 
stolon  which  increases  in  size,  its  cavity 
being  a  diverticulum  of  the  stolon -coelom. 
Fig.  286.-PonTioNoPAiuto  the  elevation  a  process  (en)  of  ihe 
Stolon  of  ^^'^^p;;-"- gndodermal  stolon-partition  extends,  and, 

(after   Kowalewsky   from  _  ^  _  '  ' 

KoRscHELT  and  heidbr).    forming    a    hollow    saclike    body,    gives 

rise  to  the  digestive  tract  of  the  bud. 
The  various  layers  give  rise  to  their 
respective  organs  with  one  exception, 
and  that  is  that  the  atrial  walls,  the  man- 
tle, arise  from  the  endodermal  branchial  sac  as  diverticula 
which  unite  together,  the  atrial  cavity  being  thus  lined 
throughout  with  endoderm.  Such  anomalies  are  not  infre- 
quent in  the  Urochorda,  and  indicate  a  necessity  for  further 
study  of  the  nature  of  the  germ-laj^ers  in  these  forms. 

The  simple  non-budding  forms  are  quite  numerous.  Com- 
mon genera  are  J/olgnla,  Cynthia  in  which  the  test  has  a 
leathery  consistency  owing  to  the  fibrillar  character  of  the 
matrix,  and  Boltenia,  a  stalked  form. 


b  =  bud. 
ir  —  braiicli  of  stolon. 
ec  —  ectiiderin. 
en  =  eudodeiiu. 


2.  Suborder  Ascidim  composite. 

All  the  members  of  thi?-  order  re])roduce  by  budding  iu 
.some  form  or  other,  and  «liffer  from  such  forms  as  ClanelUna 
in  that  all  the  individu.-' ii  remain  imbedded  in  a  common  tost 
whether  or  not  they  rem.!i5)  in  organic  connection  with  (uie 
another.     The  gmup  seemn  'a  lie  a  ^omewlsat  composite  one, 


^V 


the  body- 
is  divided 
ugitudiiial 
il  back  to 
all  of  the 
udividual. 
tweeu  the 
ice  of  the 
ins  of  all 
n  of  each 
it  arises. 
$  a  slight 
11   of   the 

its  cavity 
on-coelom. 
en)  of  the 
ends,  and, 
dy,    gives 

the  bud. 
1  to  their 
exception, 
,  the  muii- 
liverticula 
iius  liued 
not  iufre- 
jr  further 

IS. 

us.  Corn- 
iest has  Ji 
iter  of  the 


uddiiig  iu 
Clanellhia 
lumoii  tost 
1  with  one 
30site  one, 


TYPE  PUOTOCliORDATA.  ggg 

aud  it  is  probablp  Hiaf  ;* ; 

possessing  a  short  »tol„a  eLet  ,„.!  ^''Y"^'  *■"'  *'^''"'Pl«. 
former  geuus,  from  which  b  X  ^  ^  "'."^'f  '"  """  "'  ti"* 
separate  fro.  the  ^^^  ::^^^-!^~  ^^ 


^-.^ox  geuus,  trom  which  bnrla  «  •         ,  •  7  **"  °^  '^e 

«efro.  the  -oJL''u  t.T  iSj^H^  ^ 


OK  THK  TEST  (a..e.  Kow...wskv  .C  Kohs  hI.'?  r'""""'  ""^  «"«^^^^ 

«  =  parent  iudividu«il  h  ,**  . ,      '*'"'  «•=">«•»). 

*  =  *^"'<J  whicJ,  has  reached  the  Rn,.f 
c  =  migrutiug  buds  "^  '"'^''^«- 

re™t!l''a'Ct?::'lT:S^^^^^^^  «-...  .ever. 

-"lily  be  traced  b    rrthf  ^iVj  ^  '""-'■*--'.  but  can 

'""«  P<«tabdo,«eu  (FiK  287      /  """'  ''«'''™rf»  h»  a 

«;e  .toion  of  aa.^L,  .,„;  t  ttr^ril"!'";'  f-'-  'o 


i-wion  seguieiits  into 


a 


number  of  part,^  ^p 


'"Us  the 
'??.  287,  B)  which. 


630 


INVERTEBRATE  MORPHOLOGY. 


separatiug,  rise  through  the  thick  test  of  +he  parent  (Fig.  287,. 
C)  until  they  reach  the  surface,  and  develop  to  complete  in- 
dividuals,  in  which  the  process  may  be  repeated.  Amaroecium 
thus  forms  massive  colonies  consisting  of  a  number  of  quite 
separate  individuals  all  imbedded  i«  a  common  test,  and  all 
directly  or  indirectly  the  result  of  the  budding  of  a  single  in- 
dividual developed  by  the  sexual  method. 

In   other   forms,  however,  the  stolon  is  practically  sup- 
pressed and  the  buds  arise  directly  from  the   body  of  the 

b 


Ml 


Fig.   288.— a  System  op  Six  Individcms  prom  a  Compound  Colony  of 

BotrylltlS  (after  Oka). 
a  =  adult  iudiviiUial.  ecp  =  ccloilerinal   processes    extending 

b  —  bud.  into  test  from  each  Individual. 

cl  —  common  cloaca.  m  =  mouth  of  one  of  the  individuals. 

parent.  Tlu  .  is  the  case  in  Didemnum  and  Tridemnum,  for 
instance,  peculiar  complications  being  also  introduced  into 
the  process.  In  the  latter  form  the  daughter  individual  arises 
as  two  buds  which  later  fuse.  One  arises  from  the  upper  end 
of  the  oesophagus  and  gives  rise  to  the  intestine  and  neigh- 
boring organs  in  the  bad,  while  the  other,  arising  from  tlio 
branchial  sac,  gives  rise  to  that  structure,  the  atrium,  and 
terminal  portion  of  intestine.  Usually  the  two  buds  arise 
simultaneously,  but  occasionally  one  may  fail,  the  result  be- 
ing the  production  of  half  individuals  which  remain  united 
with  the  parent,  producing  double  monsters ;  and  since  either 


Colony  of 


TYPE  PROTOCHORDATA.  Q'^i 

bud  may  fail,  these  monsters  may  have  either  a  double  bran 

eo^uy,  developmg  on  one  side  of  ti.e  body  in  the  lb,,  of 

the  members  o(  the     M  IZ!  il  '""""  """'  ""■""  '"«^"  "f 

fourth  generatiora      deirrt    "  'Z  Z  tlfTT  "'™'»-^  "'  ^ 
range  themselves  so  that  they  Sate     0!^^  '°  fo™ed  ar- 

dcpvessio,.  of  the  te,t  n,.o.!Z  ,„  11     ,         """^  P°""  »'  "■W*  a 

xneeeed  eaeh  ottr tto  Z„'t,T'"*  ^"  °"""'^    "''"■  S""™""""  ">on 

a„d  so  the  oo.on;'.:r„drr  ieTtrrs;:j'';:;;,£rr'''*' 

connect  on  with  thp  nrimnai  „i«„„    u  "'«»wuuais  tailing  to  form  a 

colon,,  stni,  horvLrSdedrih^Zlotr  '"  "  ""  "'^"""« 

3.  Suborder  PyrosomidcB. 

the  central  cavity  or  cloaca  into  whid    the!    it,  f     ?" 
open,  the  br.ancltial  apertures  opening  on  ILelwT" 
cylinder.    Each  individual  'resembles  in  ,!;.^  ,  "'  ""* 

Ascidian,  the  principal  differ  cebehrthatt'llr"'^''' 
ture,  as  in  Botryllu.,  is  at  the  posteri™  end  of  t L  bo  "''"'; 
tl.at  each  individual  has  the  poler  of  repto  ,:i  gl^ddW 

parent  .o.ms  uot,  uowever,  degenerating  after  giving  rise  to. 


682 


INVERTEBRATE  MORPUOLOOT. 


buds,  as  iu  Botryllus.  The  buds  arise  from  the  branchial 
saos  behind  the  eudostyle,  and,  on  separating  from  the  parents, 
piyce  tJiemselves  oetween  them  and  the  opening  of  the  com- 
moii  cloaca,  so  that  the  okiest  members  of  the  colony  lie  at 
the  closed  end  of  the  cyli.  ler.  On  each  side  of  the  branchial 
sac  of  each  individual  near  the  anterior  end,  or  more  precisely 
near  the  peripharyngeal  ciliated  bands,  is  a  mass  of  cells 
which  are  brv.^l'fly  phosiihorescent,  the  entire  colony,  which 
may  reach  a  length  of  over  a  metre,  emitting  a  brilliant  light 
when  stimulated. 

The  development  of  Pi/rosoma  is  exceedingly  interesting 
inasmuch  as  it  presents  an  alternation  of  generations.     From 


A  B 

Fig.  289.— Lakval  Budding  of  Pyrosoma.  A,  embryo  divided  into  the 
cyatl'ozooid  aud  four  iiscidiozooids;  B,  Inter  stage  shovviug  the  asciuiozo- 
olds  twisting  to  form  the  circle  of  four  primary  individuals  (after  Kowa- 

LEWSKY). 

cl  =  cloaca.  en  =  endostyle. 

el  =  elseoblast.  /*  =  heart. 

n  —  nerve  ganglion  of  ascidiozooid. 

the  embryo  which  develops  from  the  egg  at  a  very  early 
stage  a  stolon  develops  (Fig.  2d9),  containing  a  prolongation 
of  what  corresponds  to  the  embryonic  branchial  sac  and  aiso 
•of  the  embryonic  mesoderm.  The  embryo  itself  nevei' 
reaches  a  full  development  and  is  termed  the  Cyathozooid, 
serving  to  supply  the  individuals  developed  from  the  stolon 
with  nourishment  until  they  have  reached  a  certain  stage  of 
development.  This  it  is  able  to  do  on  account  of  the  ovniii 
being  plentifully  supplied  with  yolk,  which  the  Cyathozooid 
gradually  absorbs.     The  stolon  at  an  early  staf^e  divides  iuU^ 


TYPE  PROTOCHORDATA.  633 

in   a  commou   test    ami   ,1.    f        ^'         ^^  ^-^'o^ed  with  it 
end  of  the  cvliiulnVnl  ..r^i^,  a     ''"*-"  occupy  the  closed 

.ooia  cie«e:^!;t":  a°s,/:  "2t  r  r'  ""'"^"'""- 

cloacal  cavity  of  the  coin,, 7,2  ."°™P'''  ^'^   'lisappears,   tlie 

p.-es.io„  of  t'he  tet  :t;~re;;;af  d  7""' ''' '  "«- 

imlividuals  arise  by  budding  ^     ""^  '''''''^''  "'  ""^*- 

the  first  generation  of  Botrmus  Sids  wl       ^^.^"'"^''^'d'  ^'l"«h  represents 
and  that  it  alone  degenerates  the  P^^^^^^^^^^^^^^  '"  -^  embryonie  eondition, 

listing  and  forming LrtsTfthffnir  ,  «»««««d,ng  generations  per- 
zooid  there  oeeurs  bd  nd  ^e  br  h:  7^  ^^''^  ''^'"^-  '"  "^^^'^  ^^^i^io- 
cells  termed  the  2^  Fil'  'rrlHr"'';'  ^""''^^  '"''^^^^^  ^' 
tl^ough  it  has  been  ^J^^^ii^^Z^^^  '^  ----''^i". 
larval  tail.  •'        •'  represent  the  rudimentary 

3.  Order  Thaliacea. 
The  Thaliacea  are  with  a  siugle  excenfmn  r.oi     • 
isms,  and  present  a  lifo-histo../„o2  e'aW  C  X  °'"'"'- 
rence  of  an  alternation  of  Keneratiors      T„  ,    ^  °r'"'" 

(Fig.  290)  a  well-developed  t"t  is  pi.enfa'dr''"  ^"t" 
ture  of  the  mantle  is  arranged  in  bands  wl.t..  "f™  '" 

surround  the  body  and  fuHher^l'thoVltndtn    S 
together  on  the  dorsal  surface  of  tlm  1.^  V  '^^^'e^cj  to  unite 

posterior  end  of  the  bodv  %!«     .  ^  ,      ''*"^*'^  ''^^  *^^ 

-  grouped  toJIher^oL^^tr^n^ 

(-)  lying  behind  the  branchial  sac  anrveZll  T""f " 
some  forms  the  intestine  is  more  elonrted  nnd  ^ '  T^  '^ 
Avhat  from  the  nuclen.      Tl..       ^^°"8ated  and  projects  some- 

■rm  and  positzon  ;  U  i,as  m  connection  with  it  three  pigmented 


634 


INVERTEBRATE  MORPHOLOGY. 


A 


\- 


spots  probably  represeiitiug  eyes,  and  the  subneural  gland  is 
present  as  usual. 

Each  species  of  Salpa,  however,  presents  two  distinct 
forms  {A  and  J5),  differing  in  shape  and  in  the  number  of  the 
muscle-bands  which  are  found  in  the  mantle  and  having  like- 
wise a  different  origin.  In  the  sexual  form  (A)  reproductive 
organs   are  developed,  the  ovary  usually  containing   but  a 


em 


ma 


Fig.  290.—^,  Salpa  mucronata,  the  sexttal  Potim,  and  B,  Salpa  demoera- 
tica,  THE  Non-Sexual  Form  of  Salpa  democratica-mitcronata  (after  Claus). 

c,  cl  =  cloaca.  ni  =  brauchial  pore  (mouth). 

cp  —  ciliated  pit.  ma  =  test. 

em  =  embryo.  n  =  nerve-gauglion. 

en  =  eudostyle.  nu  —  uucleiis, 

h  —  heart.  si  =  stolon. 

single  ovum.  This  when  fertilized  (em)  is  passed  into  the 
atrial  cavity,  the  follicle-cells  with  which  it  is  surrounded 
forming  an  adhesion  to  the  wall  of  the  cavity,  and  later 
modifying  to  form  a  structure  recalling  the  placenta  of  the 
Mammalian  Vertebrates  by  which  nourishment  is  conveyed 
from  the  parent  to  the  embryo.  As  the  result  of  the  devel()]i- 
ment  of  this  ovum  the  non-sexual  form  {B)  is  produced,  which 
is  characterized  not  only  by  its  general  form,  but  also  by  the 
possession  of  a  stolon  {st)  arising  from  the  branchial  sac  iust 


irPE  PBOTOcaOBDATA.  ^35 

behind  the  posterior  end  of  the  endostvie      Thi,  «(^i 
eventual^,  divides  into  a  large  number  of  pX  each    f  ^^ 
after  undergoing  certain  somewhat  complioa  ed  >;l,if;,r       i 
position  on  the  stolon,  develops  into  Z    e  fal  t^Lf 

2  r"fn^tz:',:trr  a'^^inT'^^^^^ 
iriJJrsii^i^tvs^^^^^^^^^^^ 

into  the  non.sexual  form  (Kg  291   Jri'l,.    T''  T^*^^ 
possession  of  nine  circular  m«  J!  .^     ]  diaractenzed  by  the 

.eea  some  distance  ^^:i:^:::'7t^^:, 

tlie   boay,   a   ventral   stolon   (st^   anrl   l    a        7  ^ 

directed  process  (.,,      From^t  t  olol  aribr^tT 

rior:nX-lt't::d^°  t'^  ^'^«-  — e\:?£ 

.i.emselvesZtgrattX~{rd1r^r' 
means  of  amceboid  cells,  prob.blv  n^^f.     P  *■'     .     ''^"^'  ''^ 

»ttach  themselves  in  pair;  £  t  ba'se  of  eahtd?/'"" 
to  convey  it  to  the  dorsal  process      uLn  t,  ■  ""^  ""'"^ 

Uds  arrange  themselves  inSiree  ,^„,,  t,ie  i  -r'T"',  "'" 
lateral  rows  developing  into  form,  «  ^  li" '^'"'^r'^  °^  '''^ 
resulting  from  the  development  of  the  buds  ottT  T  "'°'^ 
The  lateral  buds  when  fre^Iv  ,L    i       T        "'*'  """'"'"  '■°»-- 

the  possession  of  a  "i  t,nS°''      T  "''r'"'^"^**"  "^^ 
-     i_i„e  oiauchial  aperture,  which  occupies 


r^T-^fi^ 


636 


INVERTEBRATE  MORPHOLOOY. 


almost  the  entire  length  of  one  side  of  the  body  and  leads  into 
a  branchial  sac  whose  stigmata  ojjeu  directly  to  the  exterior, 
the  atrial  cavity  disappearing  during  the  course  of  develop- 
ment. The  intestine  is  well  developed,  but  the  muscles  are 
but  slightly  indicated,  while  the  reproductive  organs,  rudi- 


ot       en      li       St 


P'iG.  291.-^1,  Tin:  Non-sexual,  and  B,  the  Skxual,  Foum  of  DolioUim 

(after  Ulianin). 

cl  =  cloiutt.  i  -  iult-'StiiK". 

(//)  =  dorsal  process.  n  =  iifrve-giiiigliou. 

en  =  eiitloslylc.  ot  =  otocyst. 

g  =  reproduotlvu  orgau.  M  =  plinryu.x. 

h  =  heurt.  «<  -•  stolon. 

ments  of  which  were  present  in  the  young  buds,  complt'tcly 
atrophy  during  tlie  process  of  dfMelopment.  Thusc  ImuIs 
are  incapable  of  lending  a  free  existence,  serving  only  us 
nutritive  and  res])iratory  individuals  for  the  median  buds,  as 
well  as  for  the  parent,  whose  digestive  tract  deg(uierates,  its 
muscle-bands  and  nervous  system  at  the  same  time  umlor- 


OF  Doliolum 


rrPB  PUOrocilOHDATA.  J37 

goiiig  enlai-semeut,  so  tlmt  it  serves  ev^nh„?i 
iiiJiviaaal  for  the  eutire  ■,.,„,T ,     '''^"'•"'"y  •is  a  locomotor 
With  recarilU  H      "*'«"'*'"'"''  °'  ""'"iJnals. 

occur.  ctTiu  Xt;":;" '"r"  ""'"■'""-  °'  oP'-ou 

1'ei.g  set  free,  develop  ill"   '"'■*-'  '"  ™^  "-"-rit.v  all, 

■nechau  process  upou  which  bura'fotV  Tf  ''  ™''""' 
to  the  orij-in  of  these    buds  that  tL    r^  ''  '"  '"W""' 

exists.     According  to  oue  v  ew         '  T"  "'  ""'"'»'' 

ventral  process  which  is"3e. uf  aT!"'"  "?''  '""  "'^ 
Uiird  generation,  while  acm,!  f  ^,  "  "■"'  ''epreseDt  a 
certaiS  member   of    he  ma 'I  '"     »    """*'•  "^>^  "--^  -« 

tl.e  forms  bearing  thttl  ^  ' 't"  vt  X h ' ''^r"''""""; 
serving  us  nurses  for  them      TOi    .  '   "'*'«''*  ""'1 

l^owever.  the  buds  eventn.'.ll  :"'  """^  '"'  "'"'■  °"«i"^ 

'-«vid„;i.,  (f!^"'L  1  ;^^Ui:i,'rar'/"'"  ■^^^""' 

.nenced.  The  two  views  as  ioiktoXlnDju  "'  "","'- 
schematically  represented  thus :  ""  '""^'  ^« 


Ovum  =.  non-sexual  form^Nurses 


Nutritive  individuals 


-Nutritive  individuals 


f^oxual  forms— Ova 


Ovum  --.  non-sexual  form! 


'Nutritive  individuals 
'Nurses 

- S(;xual  forms Qyji 

Nutritive  individuals 


'-'«-!  into  oi,h,  iaper    1  ui^'s     tI'  '"f '  ''^  '""•«'"«  '^^'"^  1''- 

"i«k  and  lead,  nito  a  ^^:^ClZ:iJt'"T  ""  ""  '""  ""''■"-  •^'  "- 
l<"ms  and  the  inte.stine  and  vis  ,••».;  I  ';"""""  ''  ^■'""l-'.ratively 
'•-  form  of  a  nucleus.  Noth  .  '  'V't  '"  """'"'^  '""--1  ^"«<-t''«-'r  iu 
this  form.  "  '  '''  ^'^  '^""^^"  "«  to  Hie  life-histor.v  of 

Affl»it>(s  of  the   Vriirhiivih,      ti 

"■"'  M,„  ,■,,,.:,„„,„, ,:; ;; :, ■™^'i,:;;;.;;:,:.'"'" ■■•"™ '"■■  ■> la,. 

»'■"!  I....  ...any  „„„„„„„  siruolun,!   f,..    I  ,,  ""  '"'''""l"  1">- 

a I".  TI, i.,M,.,   ,/.'.,,;:"■;'''■■■',;•"'''-■  tl«„. ,„  ,„, 


chordat 


"iitin  line  of  cvolut 


I  .'iiid  ieadiny  (<>  tjw.  v„r(,.|jj.jjj.,      -j 


lie  e 


'•""■("|)res(.,it.'(|  hv  (iirl-r,,!, 


■'•Hy  stages  of  devch.i.ment 


INVERTEBRATE  MORPHOLOGY. 


638 

of  the  simple  Tunicates  (see  text-books  of  embryology)  are  so  very  siunlar 
to  those  oiAmpkioxus  that  it  must  be  concluded  that   he  evolution  ot   1 
Uvochor.iaandCephalochorda  proceeded  for  some  distance  along  sim.Ui 
lines,  and  the  general  affinities  of  the  Protoehordata  may  possibly  be  mdi- 
cated  by  a  scheme  thus  : 

Vcrtebrata 

Cephalochorda 


llemichorda 


Ancestral 


Urochorda 


'rotochordata 


T-ikinu  tlie  larval  Tunicates  as  a  basis  for  comparison,  we  And  as 
fettrnv  'on  n  o  ito  them  and  Amt>kio.us  a  dorsal  nervous  syste.n  ans- 
;« '  an  magiiution  of  the  ectod.rm  and  extending  the  entire  length 
«  the  dv  in  the  anterior  porthm.l.e  lumen  of  the  nerve-cord  expands 
::  ;!;:::;t;in  .^..^.  m  ..../<>,..  opens  in  eany  ^ages  t.  t lie ^t...or 
■i.ul  in  the  Tunicates  into  the  anterior  portion  of  the  bianchul^ac  .t, 
Z  ec  odermal  portion,  the  canal  of  communication  in  lie  latter  to.n  . 
osin  Tnl  tcf  stages  its  connection  with  the  brain  and  fon.ung  the  sub- 
^  Ida  An'urial  cavity  occurs  in  both,  which,  th.ugh  ans.ng  in  a 

^    u.    iKit  diiferent  manner  in  the  two  groups,  nevertheless  sc.nis  qu   e 
h      oU    Otis,  an.l  homologies  have  also   been   pointe.l   out  between   the 
•   r^^^^^  The  increased  lu.n.ber  of  stigmata  and  their  arrange- 

,^  U,e  Tunicates  is  a  secondary  character  resulting  probably  from   he 
:  :n;:x:s;ence  ;  and  the  development  of  the  test  and  the  H"'-.-  o  ^; 
„„(„,,,ovdtothetail  are  also  probably  see.mdary  characto.s      11".'^^' 
bhinces  are  important  one.,  ami  when  taken  into  eous.deratio„  with  the 
embryonic  development  point  very  stmuglv  to  a  close  "A""  >; 

Xs  re-mrds  the  relati<.nships  of  the  various  groups  of  I  .o<'ho.d.v  to  on., 
.noi   er  n  tsLlerabie  .lillV.vnce  of  opinion  exists.     The  Appeudu-ulanans 
"    ^      .1    .  Sim.,  se..m  to  be  the  most  primitive  of  all  the  orders   pres..,. 
rtain  remarkable  pecul.arities,  such  as  the  separate  openings  o   the  at.  1 
TviU  ^  and  the  amis,  and  some  authors  are  inclined  to  reganl  thnn  no   a 
■  u  tive  forms,  but  as  sexualiv-ma.ure  larva-  of  sessile  lonns  m  w  ue    ■ 
e«t    had  alreadv  developed  an.l  de.^eneratum  tar  a.lvaneed.     As.egaids 
^erl    ai   i"«f<nnsthesin.plc  Aseidians  seem  t<.  be  the  mos   pn.nit.ve, 
:  ;;  Lte  .om.  bemg  .lerived  from  them  by  tlu-  '-."-<- om.u 
sexual     eprodnelion.     The    composite    forms,    however,    seem    .eall>    L 
ron      en  teveral  groups  originating  independently,  all  the  members  n..t 
"    ;      l:^,M  le/froln  a,i  ancestral    simple  forn..   bn.   some  fnmi    one 
Ir  and  others  fro.u  uuother.  uuU  .o  on.     The  ThaUu..n,  tlnuUy.  ha.e 


very  siiuilar 
ntion  of  the 
long  similar 
bly  be  indi- 


TYPE  PROTOCUORDATA. 


,  wo  fliid  as 
.system  uris- 
ontirc  length 
cord  expands 
1  the  exterior 
'hial  sae,  i.e., 

latter  forms 
ning  the  sub- 
li  arising  in  ii 
a  seems  ([uite 

between  tlu; 
heir  arrange- 
)al)ly  from  th(^ 
litiition  of  the 
.  The  resem- 
itiou  with  the 

[•horda  to  onc^ 
(Midieiilarians, 
irders,  present 
ijs  of  tlie  atrial 
rd  them  not  as 
•ms  in  wiiich  a 
I.     As  regards 
nost  j»rijnitive, 
iisilioi\  of  noli 
oehi    really    I" 
'  nuMubers  not 
Dtne  from   one 
!i    lliudlv.  have 


639 

probably  been  derived  fiv»«  „ 

affinities  in  its  b^n  '^  S^t/f^'o^^^'""  ^"^^'^"^^  ^-^n 
solitary  not  necessarily  indicating  a\,rimitTv.  ?  '"'"'  ^"^'^''^"als  being 
posite  forms  no  organic  union  ext  sCe  „  t^"'  ''  """^  '"  ^"«  «"'"- 
colony  when  they  have  readied  m  ituHfv  ..  '  ''^"^"^  individuals  of  the 
rather  aggregations  than  c  I'^t  f^,"  ^'^' *'"  ^*'"^"*^^  ^-''--^^  -« 
«oc,althan  colonial  or  oven  composite  ™'  '"''**^  Properly  termed 

SUBKINGDOMMETAZOA. 
TYPE  PROTOCmiil)AT\ 

I.  Class  HEMrcHouDA.-I3ody  divided  into  three  distinet        • 

c'liord  a  .small  flngerlike  div.   H     .  '■'^"'"''  ^  "^to- 

from  anterior  po.-t  on  of  d   '  ?        '^^"J^^^"'^' ^V.rwards 
retains  connection  ^""'''''  '"''"'^  ^^'^'^  ^vinch  it 

1.  Order   I^e,v6ranc/na.  -  .sessile    colonial     f 

;'''on.se-  intestine  bent  u^;^^^^  '^^'^-^'"^'    a 

lopliophorelike,  tentacle-beirim     ,  1'  "  '''^'"'  ^^■'"' 

cus,  Rhahaopleura  °  P'ocesses.     Ceph^Uodis. 

2.  Order  E,itiroj,neusta.~Fvoo   form«  ,.  f   . 

-retingatest;  i;::3su"l"^./""'"r  "''"'^^ '   "^^ 
lophopi,orelike  ,  roc  esse       Z       ' ,      '""  '■'^''•^"  "'^ ''«"* 
n.  Class  CE.MiAL(,cHo,M)A.-Frec  form     .;  , ^"f "'"^'"-^''^-v- 

bodynotdivi:^tt:;r;;:^;;«;;;--tsecretingatest; 

ous  metameres ;  .iot<,clH  ,  ^  L  r"'  ""  I'"""- 
dige.stive  tract  and  traver.i,.  /  ^  separated  fn,,,, 
body,     .l.,;./.-,;:;;:  ''""•^'"^'  ^'"^^  -^^ire  length  of  the 

nJ.   Class  UROCHOHlu.—Sc'ssili.  r>.  f,.  ,      . 

-1  »i".wu.„  ,.„  i,„n..,.  '„'!1.' '''''"'  ■■'*""" 

1.  Suborder  .l.vcvV/m.  .v/W,  ,       1    '  "••'"""^""  a.iult. 

b-.<lding  from  stoZ  a  ,'i^       ''''  '''''^'  ^'"•'"^  "^^  else 

-ionies.,,.vario;:i:  ,;  ";;:;v;;:;''^^^ 

test.    .Simple  forms,  ^l/V,.;    "v^^^^ 

~.  Suborder  .!*<./<//«.  c..,«,..v/^,,._c;olo„ial  fonns   H 

'"<  ' V"  ..als  embedded  i„  a  ,„„.,„;  ,^  "  !  "■  various 
•""vHluals  open  into  a  com,.,.,,.  H  ,  ca  .'  '  '"  """'""•^ 
pelagic.     A,naru,iu,n^    memn   T  r        ^'^''''-  ''  "*•' 


640  INVERTEBRATE  MORPHOLOOY. 

3.  Suborder  Pyrosomidce. — Colonial  forms,  the  various  in- 
dividuals imbedded  in  a  common  test,  and  opening  into 
a  common  cloaca  ;  pelagic  ;  with  alternation  of  genera- 
tions. Pyrosoina. 
3.  Order  r/trt^woea.— Simple  pelagic  forms,  with  alternation  of 
generations.     Salpa,  Doliolum,  Octacnemus. 


LITERATURE. 

HEMICnOKDA. 

W.  C.  Mcintosh.  Report  on  Cephaludmus  dodecalophtis,  Mcintosh,  a  New 
Type  of  the  Polyzoa.  Scieut.  Results  of  the  Voyage  of  H.M.S.  Ohal- 
longer,  XX,  1887. 

S.  F.  Harmer.  Appendix  to  Report  on  Cephalodiscus.  Scient.  Results  of  the 
Voyage  of  H.M  S.  Challenger,  xx,  lb87. 

E.  R.  Lankester.  A  Contribution  to  the  Knowledge  of  Rhabdopleura.  Quar- 
terly Jouru.  Micro-scop.  Science,  xxiv,  1884. 

G.  H.  Fowler.  'The  Morphology  of  Rhabdopleura  Normmmi  Allm.  Festschrifu 
fi'ir  R.  fjeuckart.     Lciiizig,  1892. 

A.  Agassiz.     The  History  of  Balanoglossus  and  Tornaria.     Memoirs  American 

Acad.  Arts  and  Sci.,  ix,  1893. 
W.  Bateson.     The  Early  Singes  in  the  Development  of  Balanoglossus  {sp.  incerl.) 
Quarterly  Journ.  Microscop.  Science,  xxiv,  1884. 

The  Later  Stages  in  the  Development  of  Balanoglossus  Kowalewskii, 

with  a  Suggestion  on  the  Affinities  of  the  Enteropneusta.     Quarterly  Journ. 
Microscop.  Science,  xxv,  Suppl.,  1885;  xxvi,  188(5. 

The  Ancestry  of  the  Chordata.     Quarterly  Journ.  Microscop.  Science, 

XXVI,  1880. 

T.  H.  Morgan.  The  Growth  and  Metamorphosis  of  Tornaria.  Jouru.  of  Mor- 
phology, V,  1891. 

J.  W.  Spengel.  Die  Enteropneusten.  Fauna  und  Flora  des  Golfes  von  Neapci. 
Monogr.,  XVIII,  1893. 

T.  H.  Morgan.  The  Development  of  Balanoglossus.  Journ.  of  Moi'iihology, 
IX,  1894. 

CEPnALOCIlonUA. 

W.  Rolph  Untersurhungen  fiber  den  Ban  des  Amphiojus  lanceolatiis  Moi. 
piiologisches  Jahrhucli,  187(5. 

B.  Hatiohek.     Studien  iiber   Entwicklung  des  Amphioxuf..     Arbeiteu   aus  A. 

Zool.  Inst.  Wien,  iv,  1881. 

E.  Ray  Lankeater.     Contributions  to  the  Knowledge  of  Amphioxus  lanceolalns, 

YarvcU.     Quarterly  Journ.  INiicroscoj).  SiicMU'e.  xxix,  1889. 
B.  Lwoff,      Ut'ber  Ihtu  und  Entmirkiung  iler  Chorda  ivn  Amphioxus.     Millli.  (i. 

(i.  Z(»ol(>g.  Sinllou  ZL  Neapol,  ix,  1889. 
E   R.  Lankester  and  A.  Willey,     The   Derelopment  of  the  Atrial   Chamber  of 

Ainphioxtix.     Quaiteily  Journ.  Microscop.  Sciciioc,  xxxi.  1890. 

F.  E.  Weill.     Excretory  Tubules  tn  Amphioxus  lanceolatus.     Quarterly  Joiuii. 

Microscop.  Sciouce,  xxxi,  1890. 


i  a|)er   by 
Uiifv..     fj 


T^PE  PROTOCBORDATA. 


nation    of 


A.  Wllley.     The  Late     T  — '^^^^.  g^j 

V  of  the  Vertebrates.     Ne^  York,  1894. 
C.  Kupffer.     i?,-,  ^^„,„,„'^'  ^""^  «^''-  x,  1866.  ^««(/«««.     3Ienioires 

I,  1872.  ^''  -^^''^^^^iV*.    Arciiivea  do  7o.i         ^ 

H-'ieLaca.e-Buthiers      Te.  A      r  " '^  "^^^^ -'--t  geuerale. 

A-  Kowalewsky      Ced      ,    '  Archives  ,Ie 

^^     toM.ie,  X,  1874.      '     ''"^'"''^"^"ff^ierAm-dien.     Archiv  fn-     •, 

*•  van  Benaden  et  C  Juiin      A  •  ^"0"ogi., 

C  M«url«.      A   ,  '"■'■''"■<■»  ■'«  Biol.,  VI 

^"Pt'i-  bv  .>[     M     Ar  .     ,;'^''    "  Moaoqranh      Win. 

'"'^'''  °-    ''""*''      '"'"IS    ilc.pkiua 


Grorip 
roman  tj 

ACANTl 

Acant/h 

ACAKIJN 

Acervul 
Achther 
Acicvla 
Acineta, 
Aenum, 

ACCELA, 
ACOTYL 
ACRASP) 

Aclinian 
Actinovh 
Actinovii 
Aetinoph 
ActinoHpi 

ACUJ,EA1 

^^ga,  41  i 

u-EoUs,  ai 

^'Eolosomi 

^Hquorea, 

^■Eschna, 

Affalina,  I 

Agilena,  ■ 

Aglaophei, 

Afirion,  5( 

Aiptmia, 

Alc.iope,  2 

Alcippe,  31 

Alcyonai 

Alcyonclla 

AlcyonnUu 

AUyo  Ilium 

Ali,oiocu<:i 

Alpheus,  4] 


•  / 


INDEX  OF  PROPER  NAMES. 

roman  type.  capitals,  generic  names  in  italics,  and  popular  names  in 


ACANTHOCEPIIALA,  179,  183 

Acanthometra,  20,  39 

AcAUiNA.  45y,  458 

Acertularia.  17,  38 

Achtheres,  397,  423 

Acicula,  322 

Acineta,  36,  39 
Acnuta,  364 
ActELA,  132,  1G9 
ACOTYLEA,  139,  169 
ACUASPEDA, 97 

Acliniun,  114 

Actinometra,  542,  592 

Actinomma,  39 

Actinophrys,  17,  39 

Actinosphcerimn,  20,  89 

ACUJ,EATA,  ,'^27 

-*;9rt,  415,  424 

.iJolis,  315,  304 

^-Eolosoma,  219.  251 

^■hJquorea,  80,  116 

^■Eschna,  noo,  526 
Af/alma,  92,  116 
Agdena,  450,  458 
Afilmphenia,  87,  116 
Av'Vo//,  506.  526 
AipUuia,  113.  117 
Ali'iopc,  212,  251 
Alrippe,  399,  423 
Ai.cYONAiu/i';,  108,  117 
Alcyondla,  261,  274 
AlcyonuUum,  261,  274 
Alcyouium,  108,  117 
ALi,oi<»ca:LA,  133,  169 
Alp/ieus,  412,  424 


Amaroecium,  629,  689 
Amceba,  15,  38 
Amphineuka,  284,  363 
Amphioxus,  608,  639 
Amphipoda,  416,  424 
Amphiporus,  167,  170 
Amphitrite,  213,  251 
AvqMura,  564,  592 
Atnpullaria,  308,  364 
Anubolia,  515,  527 
Aiiachcftu,  218,  251 
Anulgen,  453,  459 
Anasii,  510,  ,527 
Anchorella,  397,  423 
A)iel<mna,  402 
A^'l^s()PODA,  413,  424 
Annelida,  202.  251 
Auodon,  339,  365 
Anomiit,  3,3!),  365 
Antedoii,  ,542,  592 
Anthomeuls/E,  87,  116 
Antifo/oa,  104,  117 
Antipiiihnriii;  m,  117 
Ants,  518 
Anthiira,  414,  424 
Anunda,  503,  526 
Apiiid/k,  510 
vlp//M,  .'527 
J/>/»,  518,  527 
Aplynia,  313,  364 
Apod  A,  593 

Api^ixliculiiria,  636,  089 
ApHindiH,  414,  424 

APTEt; 


luuiA,  .wi,  526 


-4j!JM«,  387,  423 


648 


€44 


INDEX  OF  PROPER  NAMES. 


ii 


AUACIINIDA,  435 

AuANii.«,  448,  453 
Arbacia,  580,  593 
Area,  339,  365 
Aveella,  16,  38 

AUCIUANNKUD^,  211,  251 

Archigetes,  161,  170 
Aricia,  309,  251 
ArenicoUi,  209,  251 
Argiope,  271,  274 
Argonauta,  359,  365 
Argulus,  397,  423 
Avion,  316,  364 
ArmadiUidium,  414,  424 
Artemia,  386 
AuTHKoroDA,  368,  523 
AUTUHOSTKACA,  413,  424 
Ascavis,  48,  177,  182 
AsciDiACE.K,  627,  639 
Ast'ioi/K  coMi'osiT^:,  627,  639 
Asciui^:  siMrucES,  627,  639 
Asc'iiUiins,  617 
Ascopodaria,  256,  274 

ASCOTHOKACIDA,  403 

Asellus,  414,  424 
Asperg ilium,  329 
Aspidiotits,  510,  527 
Asplanchna.  189,  200 
Asterias,  550,  592 
Asterina,  552,  592 
Asi'EKOiDEA,  552,  592 
Asthenosoma,  570,  593 
Asirangia,  114,  117 
Astropectcn,  556,  592 
Aslrophi/toii,  561,  593 
Atalanta,  309,  364 
JKaiC,  453,  459 
AtropoK,  509,  526 
^«««,  451,  458 
Aitrelia,  101,  117 

AUTOFl-AGKLI-ATA,  28,  39 

AiUolytus,  212,  251 

Balanoglossus,  601,  639 
Balamis,  400,  423 
Baruiicles,  398 

UA8OMMATt)PU0UA,  317,  364 

lidellara,  136,  170 


Beacliflea,  416 
Bees,  518 
Beetles,  512 
Belemnites,  360 
Iklostoma,  510,  527 
i?,'?w,  121,  126 
Bipalium,  136,  170 
Z?M-5r«s,  412,  424 
Blastoids,  550 
Bolina,  124,  126 
Bolteuia,  628,  639 
Bombus,  518,  527 
Bonellia,  241,  253 
Jiook-seorpion,  444 
Bopyrus,  415,  424 
Bothriocephalus,  153,  170 
Botvyllus,  631,  639 
BntchiiiHS,  513,  527 
Brachiontts,  189,  200 
Bkachiopoua,  268,  274 
Bkacuyuka,  412,  424 
Branchellion,  228,  253 
Buanciiiopoda,  885,  423 
Bvanchiostoma,  608 
Branchipus,  386,  123 
Bkanciiiuka,  397,  423 
Brisinga,  553,  593 
Bnstle-tails.  501 
Hrillle-stiirs,  561 
BiiYozoA,  355 
Biigi,  510 
Bugula,  ,262,  274 
jB«;/«,  313,  364 
i?«</tHS.  443,  458 

Ciuldistiies,  5lS 
CiuinlHS,  322,  364 
Valamocrinus,  544,  593 
Calanus,  396,  423 

CAIiCAUEA,  73,  115 

fa^ti/Ms,  396,  423 
CalliiiecUs,  412,  424 
Caloptenus,  504,  526 
Citlonoma,  513,  527 
Calyptrmx,  307,  364 
Cambarue,  412,  424 
Campanulahi^:.  85,  116 
Ciimpodea,  502,  526 


Campi 
Campi 
Cancti 
Canthc 

C<ipreU 

Varabii 

Caravtu 

Carina 

Carinel 

Varpocu 

<Jaryop) 

■Cecidom^ 

Oentipe( 

Cei'iiai, 

Vephaloi, 

Ckpiial( 

CephaloU 

Ceratium 

(j^ercomoi, 

Cerebralu 

C'khiant 

Cerianthi, 

Cestoda, 

Cesium,  1; 

CetocJiilus, 

Chatobran 

CJut'toderm 

Chalogmte 

Chcetonotus 

<'h(irybdea, 
Vhelifer,  44 
Ohernes,  44. 
Chilodon,  'M 

('IlILoCiNA-ri 

<'II1L()ST0MA 

<'liirodota,  Tii 

('liiton,  289, 

C'^iitonellufi,  S 

f'lilamydomoi 

Cliondracantl 

^''irysopa,  51^ 

<'V>rt«W,  510,  S 

^'inndela,  513 

QidariH,  530,  j 


IJSDEX 


(^amponotus,  518,  n^l 
Campylaspia,  408,  434 
Cancer,  413,  424 
G^mthocamptm,  806,  433 
Capitella,  206,  251 
Capretla,  416,  434 
(Jm-abus,  518,  527 
Garavdla,  92,  116 
Cariiuiria^  309,  364 
Garinella,  106,  170 
C'arpocapm,  516,  527 
<!aniophyU,vus,  153,  17Q 
Oecidomyia,  60 
t'entipedes,  484 
Oki'iiai.ociiohi)a,  608,  639 
^(ip'ialodiscvs,  ,')97  639 
CKPiiAU)i.„OA,  340.  365 
GfphalothrU,  169 
Veratium,  30,  39 
(Jerconionas,  31,  39 
<^erebmiulus,  116,  170 
(-'kkiantiik^;,  110,  117 
Cermnthus,  110,  1 17 
Ckstoda,  152,  ITO 

('etocJiilus,  896,  433 
f^'JMiohrancliuH,  218  351 
Gfic'toderma,  285,  364 
Ofiwlogmter,  223,  251 

J|".KT«>(iNATnA,  186,  200 

^iKHoHotus,  196,  200 

C|h^:t()poda,  304,  351 

('/Kirybdea,  101,  II7 

('fielifer,  443,  458 

Oheriies,  444,  4,158 

Vhllodon,  34,  39 

OlIILofjNATHA,  483 

C'lULopoDA,  484,  525 

<'iiju)sToMATA,  262,  274 

C'nrodota,  .585,  593 

^''''ito/i,  389,  864 

(^"litimelhts,  388,  364 

fl'lumydomonas,  31,  39 
^''ondracnnthm.  397,  423 
<-''iryaopa,  514,  527 
^^wififffi,  510,  537 
<^<<-indeia,  513,  537 
ft'/'*m,  530,  593 


CiLIATA,  33,  39 
C'lUiuiiPKDiA,  398,  433 
C'l-ADOCKUA,  388,  423 
(-''urn,  339 
Clat/irulina,  18,  39 
tVaoa.  87,  116 
ClavelUna,  637,  639 
Clej)sine,  336,  253 
6Vitf/<«,  74,  1J5 
CVi.Me,  814,  304 
Clmocainpu,  5i6,  537 
('iymeneUu,  304  ' 
OlypeoMer,  581,  593 

Cmi.kastuoioka,  581,  593 
f-<'A««,  513,  537 

^'NIUAHfA,   76,   116 
COCCID/K,  510 
(^'OCCIDIA,  34 

Cocci iiella,  513,  527 
t'ockroiicli,  504 
Codosifja,  28,  89 
Cuil.KNTKKA,  68,  115 
Cmloplmm,  135 
Coi.Ecn'TKUA,  512,  527 
COLLKMHOLA,  503,  526 
CoUosHendeift,  464 
Colpidiiiw,  37,  39 
Volpoda,  36.  39 
Coiivolutii,  182,  169 
CoiMci'ODA.  393,  423 
C'oial,  114 

Coraltium,  108,  117 

t'ouNAcusroNoiA,  73,  115 
Cwophiiim,  417,  424 
CoHUODKNTfA.  507,  526 
GorycivuH,  396,  433 ' 
Corydali8,  514,  527 
^w^/ic,  87,  116 
CoTYMiA,  139,  170 
Cml)s.  412 
Cmnia,  271,  274 
Oniylislj,  413 
Crickels,  504 

CJiiNoiDKA,  541,  593 
Cvisia,  274 

CriHtateUa,  260,  274 
CnusTACKA,  368 
Chyptopkntameha,  527 


645 


646 


INDEX  OF  PliOFER  NAMES. 


Cryptophialus,  399,  423 

C'jiYPTOTETUAMEHA,   527 

Cteniza,  452,  458 
CteiiodHlus,  58,  222 
Ctenopiiora,  120,  126 
Ctenoplana,  125 
Ctenostomata,  262,  274 
TUBOMEDUS^.  101, 117 
Cucumaria,  585,  593 
Vulex,  520,  528 
CuMACEA.  407,  424 
Cunina,  96,  116 
Cunqctantha,  84,  116 
CURCULIONID.E,  512,  527 
Cuspidaria,  ;i89,  365 
Cyamua,  416,  424 
Cyanea,  101,  116 
Cyclnti,  3:39,  L 
Cyclops,  396,  -.  ,!3 
Cyclostoma,  30t   '    4 
Cyclostomata,  262,  274 
CymhuUopm,  314,  364 
Cymothoa,  415,  424 
Cytiips,  518,  528 
Cynthia,  628.  639 
Cyphopliihulmus,  447,  458 
(Vp^vpa,  307,  364 
Cypridina,  391,  423 
C:y;»'is,  391,  423 
C'ystoflagellata,  30,  39 
Cystolds,  550 
Cy there,  391,  423 

Dactylopius,  510,  527 
Daphnia,  388,  423 
Daudebardia,  316,  364 
Decapoda  (Cepbiilopoda),  359,  365 
Decapoda  (Crustacea),  410,  424 
i)emrf,  585,  593 
Demodex,  453,  458 
BendrociBlum,  136,  170 
Dendrognster.  403,  423 
Dentalinm,  323,  364 
L'-rmnlekhus,  453,  458 
Deumapteua,  504,  526 
/fero,  218,  251 
Desmosticha,  580,  593 
Dindema,  580,  593 


Diopheromera,  505,  526 
DiantyliH,  408,  424 
Dibkanciiia,  359,  365 
Dicyema,  64 
DiCYEMiu.*;,  64 
Dideinnum,  630,  639 
Difflugia,  16,  38 
Dinobryon,  28,  39 
Dinoflaoellata,  30,  39 
DiiiophUuH,  198,  :iOO 
JJiopaira,  212,  251 
DioivcAUDiA,  305,  364 
Diphyes,  92,  116 
Z>«>?(!«a;,  506,  526 
DiPLopoDA,  482,  525 
Diplozoon,  147 
DiPNEUMONEs,  452,  458 
Diporpa,  147 
DiPTEUA,  519,  528 
DiscoMEDus^:,  101,  117 
IJincosoma,  114,  117 
Distaplia,  629,  639 
DiSTOME^,  147,  170 
Distomum,  147,  170 
Dochmius,  177,  182 
LoUolum,  635,  640 
Uuiidermi,  287,  364 
Z>o?'M,  315,  364 
Boryphora,  513,  527 
Dragou-flies,  506 

Earwigs,  504 
EcAuuiNEs,  269,  274 
Echinarachnius,  r81,  593 
Echinocucuntis,  585 
ECIIINODEKA,  184,  200 
Echinoderes,  184,  200 

EciIINODEUMA,  531 

EcHiNoiuEA,  570,  592 
Echinorhynchus,  180,  18S 
EciiiuuE,*;,  240,  252 
Echinrns,  240,  252 
EcTOPuocTA,  257,  274 
Edriophthalmata,  413 
Edwardsid,  117 
EowAKDsi^:,  109,  117 
Elasipoda,  585,  593 
Er.ATEKin.K,  513,  537 


Elpidi 

Endo] 

Ensate 

Enteh 

Entom 

Entoni 

Epeira, 

Epherru 

Epheme 

Ephyda 

ErgasUi 

Eruani 

Esperell, 

Estheria 

Eucope, 

EUCOPEI 

Eudendi\ 
Euglena, 
Euglypha 
EULAMEI 
EnNEMAl 

Eupagun 
Euphausu 
Euplectelli 
EuRYALrn 
Eurylepta, 
JSurypaui't 

EURYPTER 

EuTypterus 

EURYSTOM] 

Eiiscorpius, 
Empongia, 
Evadne,  38fe 

EacelUna,  3 
Eilaria,  177, 

FiLIBRANCH 

Eiona,  311 
Fissurella,  3( 
Elagellata 
I'^Jies,  519 
Eloscularia^ 
^''lustra,  261, 
EoHAMr]snFEp 
^orficula,  50J 
Formica,  518, 
Fredericella,  2 
^nngia,  Hi,  1 


IN3BX  OF  PROPER  NAMES. 


Elpidia,  585,  593 
Endoprocta,  256.  274 
Enmtella,  339,  365 
Enteropneusta,  601,  639 
Entomostraca,  385,  423 
Entoniacus,  415,  424 
Epeira,  450,  458 
Ephemera,  504,  526 
Ephemeridce,  505,  526 
Ephydatia,  73,  115 
Evgasilua,  396,  423 
Erkantia,  211,  251 
Esi)ereUa,  75,  115 
Estheria,  387,  423 
Eucope,  86,  116 
Eucopepoda,  396,  423 
Eudendriutn,  93,  116 
Euglena,  29,  40 
Euglypha,  16,  39 

EULAMELLIBRANCHrA,  339,  365 
EUNEMATODA,   174,  182 

Eupagurus,  411,  424 
Euphauaia,  406,  424 
Euplectella,  74,  us 
EuRYALiDA.  569,  592 
Eurylepta,  139,  no 
Eurypauropus,  482,  525 

E  UR YPTERID^,  433 

Eurypterus,  433 
EuRYSToME^j,  125,  126 
Euscorpius,  443,  458 
Euspongia,  73,  115 
^i'ttcJwe,  388,  433 

FacelUna,  315,  364 
Eilaria,  m,  iS2 

PlUBRANCHIA,  339,  365 
Eiona,  311 

Eissurella,  305,  364 
Elagellata,  28,  39 
Elies,  519 

Elosculana,  189,  200 
Eliistra,  261,  274 

EoRAMlytFERA,  15,  39 

Eorficula,  504,  526* 
Formica,  518,  527 
Eredericella,  260,  274 
Eungia,  114,  117 


647 


Galeodes,  445,  458 
Oamasus,  453,  459 
(^arnmarua,  416,  424 
Gasteropoda,  293,  364 
(iaateiopteron,  313 
Oecarcinua,  412,  424 
Oelaaimua,  412,  424 
Geometrid^,  517,  527 
Geophilua,  484.  525 
Gepiiyrea,  237,  253 
(^eryonia,  85,  il6 
Oibbocellum,  447,  458 
Olobigerin",  17,  39 
Olomeria,  483,  525 

Gnathobdellxd^,  236.  251 
l^onactinia,  111,  117 
Oonodactyhta,  409,  424 
Oonoleptua,  448,  458 
GoRDiACEA,  178,  183 
Gordiua,  178,  183 
Gorgonia,  108,  I17 
Grantia,  73,  115 
Giasslioppeis,  504 
Gregarinida,  24,  39 
Gromia,  16,  39 
Gryllotalpa,  504,  526 
Gryllua,  504,  526 
G'j^jfte,  136,  170 
Gyainol/emata,  261,  274 
Gymnosomata,  314,  364 
Gyrinna,  513,  527 
Gyrodactylua,  14  7,  179 

Il'vmenteria,  236 

Ilalcampa,  113,  II7 

Halecium,  87,  116 

HalioUa,  305,  364 

lialiaarca,  74,  115 
Ilnlohates,  510,  527 
Halorypris,  391,  403 
Halodrilm,  227 
Harpacticus,  396,  423 
■'^'rpahia,  513,  527 
Harvest-men,  448 
Harvest-mite,  453 
Harvest-spider,  447 
JIdiopora,  109 
Uelioaphmra,  I9,  gg 


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648 


INDEX  OF  PROPER  NAMES. 


Heliozoa,  17,  39 
Helix,  316.  364 
Hemichokda,  596,  639 
Hemiptkka   510,  527 
Hermit  Crab,  411 
Heaione,  207,  251 
Heterodera,  176,  183 
Heteuomeua,  527 
Iletei-onereis,  216 
Heteropoda,  309,  364 
Heterotuicha,  40 
Hexactim^,  113,  117 
Hexarthra,  194,  200 
Eippa,  411,  424 
Hirudinea,  228,  251 
Hirudo,  236,  251 
Uolopus,  541,  592 
Holothuria,  585,  593 
HOI.OTHUROIDEA,  584,  593 
HOLOTRICHA,  40 

Homariis,  412,  424 
HOMOPTERA,  510,  527 
HOPLONEMERTINI,  167,  170 

Horseshoe  Crab,  428 
HVALOSPOl.GI^.    74,  115 

Ilydra,  58,  83,  116 
Hydrnchna,  453,  459 
Uydractinia,  58  87,  116 
Hydrari.*:,  83,  116 
Hv'DUOCORALMN^.,  89, 116 

Hydromedus/E,  78,  116 
Hydrometra,  510,  527 
UydropJiilus,  518,  527 
Hymenoptera,  517,  527 
Ilyocrinua,  542,  592 
Hypotriciia,  40 

lanthina,  807,  864 
ma,  401,  428 
Ichneumon,  528 
Ii'hthydium,  196,  200 
IcIMyolHleUa,  228,  252 
Tdotea,iA\  424 
Idyia,  125,  126 
Infusoria,  38,  40 
Inbkcta.  487,  52C 
/«>.  108,  117 
IsopoDA,  414,  424 


lulus,  483,  525 
Ixodes,  453,  459 

/awM«,  311,  364 

King-crab,  428 
Kolga,  589 

Labia,  526 

Lacmularia,  189,  200 
Lam::li.ibranchia,  326 
Lampyris,  513,  527 
Larvacea,  626,  639 
Laura,  403,  423 
Leiobunum,  448,  458 
Lepas,  399,  423 
Lepidonotus,  212,  251 
LEPiDOPTEr,A,  515,  527 
Lepisma,  502,  526 
Lepiodiscus,  3C  39 
Leptodora,  418 
Leptogorgia,  108,  117 
Leptomedus^,  85,  116 
Leptoplana,  139,  170 

Leptosthaca,  404,  423 

Lernom.  397,  423 

Leucosolenia,  73,  115 

Libellula,  506,  526 

Libinia,  412,  424 

Ligula,  152,  170 

Limacina,  814,  364 

Limapomia,  315,  864 

Limax,  316,  864 

Limnadia,  387,  423 

Limuaa,  316,  364 

Liinnetis,  887,  428 

Limulus,  427 

IJnguln,  271.  274 

LioVieum,  509.  526 

Liriope,  85,  116 

Lithobius,  485,  525 

Lobster.  412 

/x>%o,  359,  865 

Lopfiopus,  261,  274 

Lo^rosorna,  256,  274 

l.ucei'naria,  100, 116 

Zuci^fr,  411,  434 

iT.T/iV^ui,  568,  692 


LUM 

Lum 
Lycoi 
Lysic 
Lysio 
Lyttu 

Macrc 

Macro 

Macr< 

J*Iacim 

Mad  I  e^ 

Malucc 

Malac 

Malac 

AfALAC( 

Malac< 
Malloj 

Margeli, 
May-fly, 

Melicertt 
M-llita, 
Meloe,  5] 
Melolonti 
Melophai 

Membran 

Mernm,  ] 

Mertensia 

Mesostovu 

Mesozoa, 

Metazoa, 

Metridium 

Mierogaxle 

Microgrom 

MrcHoLEp 

Microstoim 

Miliola,  16, 

Millcjxira,  i 

^'illipodes, 

Elites.  453 

Mnemiopttia^ 

Modiolaria, 

yfoina,  388, 

^foira.  588, 

'^(olguld,  62f 

Molp<i,ii^,^  5{i 
Monns,  2«,  4, 


LUMLRICOMORPHA,  251 

Lumbricus,  233,  251 
Lycosa,  452,  458 
Lysiopetulum,  483.  535 
Lystosquilla,  409,  434 
Lytta,  513,  527 

MacrohdeUa,  236,  252 
Macrobiotus,  467 

MAcnoLEPiDoPTKiu.  516,  527 
AlAcuuRA,  411,  424 
Madiepora,  114,  117 
Malacobdella,  167,  170 
MalacobdelunI.  167.  170 

^ALACODERMATA,  114.  117 
J»'ALACOPODA.  475 

Malacostraca,  403.  423 
Mallophaga,  509 
Margelis,  87,  116 
May-fly,  505 

Melicerta,  189.  200 
MHhta,  581.  593 
Meloe,  513,  537 
Melolontlui,  512,  527 
Melophagua,  fi'iO,  538 
^enibranipom,  261,  274 
^Wcm«,  178.  183 
Merteiisia,  124.  126 
Meaostomi,  135,  169 
Mesozoa,  63 
Metazoa.  41 
Metridiinn,  lU,  II7 
■^fin-offimer,  518,  528 
^ficrogromia,  21.  39 
MrCROLEPIDOPTERA.  513   62V 
^^r««to;««.  58.  135.  140.  169 
-l/«/<o/^r.  16.  89 
^fillejwra,  89,  116 
^'illipodes,  482 
Mites.  453 

^^f^'iemiopsis,  124,  lag 
Modlolnria,  339,  365 
Al'iwrt,  388.  423 
^toira,  583.  593 
^folgula,  628.  639 
MoLMjst'A,  376 
^olpddia,  598 


/A-i>i.X  OF  PROPER  NAME8. 


649 


Monostomum,  147,  170 
MoNo'iOcARDIA,  306,  364 
MoHoius,  134.  169 
Aimeria.  585,  593 
'l/Msca,  020.  5^i8 
Musse),  339 
^y<i,  339.  365 
^Vfi'tf^c,  451,  458 
Myriapoda.  480,  525 
^yrmeleon,  51-,  537 
%*«■«,  406,  424  ' 
MytilHH,  339,  3g5 

Myxosporidia,  26,  39 
Myzostome^.  244,  253 
Myzostoinum,  244,  252 

^ArDOMORPHA,  251 

NaiH,  227,  251 

Narcomedih^,  84  116 
Natica,  307,  364 
Nautilm,  357,  365 
Nebalia,,  405,  423 
Necrophorus,  .^12,  .527 

Nemathelminthes,  172  isq 
NE1.IAT0DA,  173,  182 
Nemertina,  162,  170 
Neocrinida,  551 
'N,'omenia,  286.  364 
^ephelis,  236,  251 
^V«-cM.  218,  251 
^eritina,  305,  364 
Neuh„ptera,  514.  537 
Jyoctiluca,  31^  40 
Nodomrut,  17  39 
Nothrxis,  453.  459 
^otoaelphys,  396,  438 
J^'otonecta,  510,  527 
Numla,  339.  365 
NoniBKANCHiA.  815,  364 

^*('/«V/.  86.  116 

Obtsiuvi,  444.  4,58 

Octacnemus,  637.  639 
OcTopoDA.  359,  866 
^^c<tfpM«.  359  365 
Ocuiina,  114 
<><'ypodn,  412.  434 
<Ji>ONATA,  506,  536 


650 


INDEX  OF  PROPER  NAMES. 


Oligoch^ta,  218,  251 
OinmastrepJm,  359,  365 
Onchidium,  316,  364 
Oniacus,  414,  424 
Onychophora,  475 
Opalina,  36,  39 
Ophiacti8,  566,  592 
Ophioderma,  561,  592 
Oplmlepia,  567,  592 
Ophiomyxa,  561,  562 
Ophiothrix,  564,  592 
Ophiura,  592 
Ophiubida,  569,  592 
Ophiuroidba.  561,  592 
Opilio,  448,  458 

OPISTHOBRANCHIA,  310,  364 

Oractis,  111,  117 
Orgyia,  516.  527 
Oribatea,  453,  459 
Orthonectida,  65 
Orthoptera,  504,  526 

OSTRACODA,  391,  428 
Ostrea,  339,  365 
Oxyuris,  177,  183 
Oyster,  339 

Palmmon,  413 
Palmmonetes,  412,  484 
Pal^kocrinida,  551 
Pal^onemertini,  166,  170 
Palinurua,  421 
Paludicella,  261,  274 
Paludina,  807,  864 
Palythoa,  112.  117 
Pandartta,  396,  428 
Punorpa,  514,  527 
Panorpata,  514,  537 
Papilio,  527 
Paranmcium,  85,  89 
Patella,  305.  864 
Pauuopoda,  481,  535 
Pauroptia,  482,  525 
P<jc/(jn,  839.  365 
Pedalion,  195,  300 
Pedata,  593 
Pedicellina,  266,  274 
Pidiculua,  510,  527 
Pkdipalpi,  446,  458 


Pelaffia,  103,  117 
Pelecypoda,  326,  865 
Pelmatozoa,  551 
Pemphigua,  511,  527 
Penma,  419,  424 
Penella,  397,  428 
Pennaria,  87,  116 
PennatuUi,  109,  117 
Pentacriiiua,  542,  592 
Pentamera,  527 

PENTASTOMIDifi,  461 

Pentaatomuvt,  461 
Perichceta,  218,  251 
Peripatua,  474,  525 
PeHplarwta,  504,  526 
Peritricha,  40 
/"cWa,  507,  526 

PEROMEDUSiK,  101,   116 

Perophora,  627.  639 
Petalosticha,  f)83,  593 
Phagocata,  136,  170 
Phalangida,  447,  458 
Phalangium,  448,  458 
Phaacolion,  242,  252 
Phaacoloaoma,  242,  253 
Philichthya,  897,  423 
PhUodina,  189,  200 
Phlmthripa,  510,  526 
P/<ote«,  339,  365 
PHORONID.E,  247,  252 
Phoronia,  247,  252 
Phoxichilidium,  464 
Phryganea,  515.  527 
Phrynus,  446,  458 

PUYLACTOLiKMATA,   261,  274 

Phyllirhog,  316,  364 
Phyllopoda.  385,  423 
PItymanthus,  114,  117 
P%«a,  316,  864 
Physapoda,  509 
Phyioptua,  454,  458 
P/em,  616,  527 
Pinnotherea,  412,  434 
Piacicola,  286.  252 
Plagioatoma,  188,  16ft 
Pianaric,  136.  170 
Planocern,  136.  170 
PlanorbU,  310,  364 


IlfDBX 

Platthelminthbs,  127.  m 

1  Mtyonychus,  412,  424 

Pi^KcopTiSRA,  507,'626 
Pleurobrachia,  124,  126 
Pieurobranchaa,  312 
Plevrobrayichus,  313,  364 
PleurophylUdia,  315.'  364 
PieuroUmariu,  805,  364 

Pneumodernia,  314,  864 

■Podura,  503,  525 

POLYCH^TA,  204,  251 

POLYCLADEA,  138,  170 

PolydeHinus,  483,  525 
Polygordius,  21  J,  251 
Polyophthalmus,  209,  351 
Polyphemus,  388,  428  ' 
Por.YPLAcopHORA,  288,  864 

POLYSTOME^j;,  147^  170 

Polystomum,  147,  170 

PoLYzoA,  255,  274 

Pontobdella,  236.  253 

Porcellana,  41J<,  424 

Porcellh,  414.  424 
POHIFEHA,  69.  115 
Porosporx,  25 
Porpita,  91,  116 

Portuguese  Man-of-war,  98 
ri'Kipulus,  24'3,  252 

Proctotruprs,  518,  528 

Proneometiia,  285,  364 

ProrJiynchus,  135,  169 

Pkosobhanchia,  303,  864 
PnosoPYGiA,  254 
PftOTACTiNr^a,  J 11.  117 
Proteolepas,  402,  423 
Pkotouhanchia,  388,  365 
Photochoruata,  596 
Protodrilu8,  211 
Pkotozoa,  13,  89 

Pu..TUAci,EATA,  474,  625 
t^rotula,  215 

muDosconPioNiDA.  443.  458 

P8<)CIDA^  509 
-fto/wa.  584.  593 

Ptbrobhanciha,  597.  689 
tteromnlus,  518,  528 
Ptkuopoda,  813.  864 


OF  PHOPBH  NAMES. 

f  ^rotrachea,  809,  864 
Pteryoota,  504,  526 
^'^^e*.  520,  528 
PULMONATA,  816.  864 
PVCNOGONIDA.  468 

Pyralid^,  516,  527 
Pyrosoma,  631,  640 
Pyrosomid^,  681,  640 

Radiolaria,  18,  89 
Runatra,  510,  527 
Razor-sliell,  389 
lienilla,  108,  117 
Jihabditia,  176 
JJ^^co^i-A.  134.  169 
iihabdopleura,  597,  639 
Rnegmatodes,  86,  116 
liHIZOCEPHAi^A.  402 

lihmcrinus,  P^.  593 
Rhizopoda,  U,  39 

liHJZOSTOMlD^,  102 

Rhopalodina,  584,  593 
lihopalonema,  85,  ng 
iihopalura,  66 

Rhtnchobdellid^,  236  251 
^%«c/.««,;^„,  272  274 

Rhynchota.  510,  527 
Vtoto^m.  17,  39 

PoUJera,  189,  200 

-^aftflWa,  212,  251 
f^culina,  402,  423 
*'.<7rtto,  186,  200 
<»'<?««»•«,  570,  593 
^Ipa,  638,  640 
8and-dollar,  581 
^Perda,  512,  527 
^Pphirina,  396,  423 
Sarcopte^^  453.  459 

Sarcohpoiudia,  27.  39 

Scalaria,  808.  364 

Snilloj),  339 
^alpellnm,  400,  428 
S(  APir„p„iM,  322,^864 
ScinzoNKMEuTiNr.  166.  170 
ScmzoPoDA.  406  424 

SCLEHODKIIMATA,'  1  i'4    It? 

Scolopendra,  484.  625  " 


651 


662 


INDEX  OF  PROPER  NAMES. 


Scolopendrella,  486,  525 
Scorpiou,  441 
ScoupioNiDA,  441,  458 
Scrtipocellai'ia,  261,  274 
ikvt:  -era,  485,  525 
"w«,  431 

iSCYPHOMEDUSiE,  97,  116 

Scytophorus,  111,  117 
Sea  Aueiiiones,  114 
Sea-lilies,  541 
Sea-urcbius,  570 
Sedentaria,  213,  351 
Segestria,  453,  458 
Selandria,  519,  528 
Sepia,  359,  365 
Septibuanchia,  339,  365 
Sergestes,  411,  434 
Serpula,  313,  351 
Sertularia,  86,  116 
Ship-wonn,  339 
Shrimp,  413 
SitUi,  388.  433 
Siphonodentaiium,  822,  364 

SiPHONOPHOKyE,  91,  116 
SiPUNCULACEA,  241,  253 
Sipunculus,  343,  253 
Siriella,  407,  434 
Sitaria,  513 
Slavina,  333 
Solarium.  808,  364 
Soi,ENOGASTUE8,  285,  364 
SoLiPUG^,  444,  458 
Solpnga,  445.  458 
Sow-bug,  414 
Spadella,  186,  300 
Spatangua,  583,  59" 
Spharoma,  415,  434 
Spharozoon,  19,  89 
Sphyranura,  147,  170 
Si'icuLiapoNGi/B,  74,  115 
Spider,  448 
Spirula,  359.  305 
Spondylus,  335 
Sponges,  69 
Spongilla,  78,  115 
Spokozoa,24,  89 
Spring-tails,  508 
S<i>iiUa,  409,  424 


Staphylinid^e,  512,  537 
Starfish,  553 

STAUROMEDUSiE,  100,  116 

Stentor,  35,  40 
Sternaspis,  343 
Stomatopoda.  408,  424 
Sloinclophus,  101,  117 
Slouu-aies,  507 
Stroml/ua,  307,  364 
Strongylocentroiua,  r)80,  593 
Strongylosoma,  184,  520 
Stylaster,  90,  116 
%;eWrt,  314,  364 
Siylochus,  141,  170 

STYLOMMATOPnOUA,  318,  364 

Stylonychia,  40 
SucToiUA,  30,  40 
Sim-animnlcule,  17 
Syllia,  313,  351 
Symphyla,  48C,  536 
Synapta,  633,  040 
Synccelidium,  186,  170 

Tabanus,  520,  528 
Tmnia,  153,  170 
Tanaia,  414,  424 
Tanysiylum,  463 
Tardigrada,  466 
rc«Jja,  113,  117 

TECTIBRANCHfA,  313,  364 
Tegenaria,  45(t,  458 
7e/«i,  517,  537 
Tentaculata.  134,  126 
TfTPhella,  213,  351 
Terebkantia,  537 
Tevebratulina,  371,  274 
Teredo,  839.  365 
Tfe/'me.'i,  508,  526 
Termites,  507 
Teaa&ra,  100,  116 
tk8ticahdine8,  269,  274 
Tetrabranchia,  857,  365 
Tetranychua,  454,  459 
Tetrapnettmones,  452,  458 
Tetraatemma.  167,  170 
Textularia,  17,  89 
Tualaaaema,  241,  253 
niamsaianthua,  114,  117 


INDEX 


TliaUmicolla,  18,  39 
Thaliacea,  633,  640 
Thaumaiocrinus,  543,  593 
Thecasomata,  314,  364 
Thelyphonus,  446,  458 
Theridium,  450,  458 
Thohacostraca,  406,  434 
Thripa,  510,  536 
Thyone,  587.  593 
Thtsanopteka,  509,  536 
Thysanozoon,  139,  170 
Thtsanura,  501.' 636 
Ticks,  453 
Tinea,  516,  537 
Tracheata,  469 
Trachydermon,  289,  364 
Trachymedus^,  85,  116 
Trematoda,  143,  170 
Tremoctopua,  859,  365 
TrianopJm-ua,  153,  170 
TricJiaater,  569^  593 
Trichina,  176,  183 
TrichoeepJialua,  177,  183 
Trichodectea,  509,  526 
TricJioplax,  63 
Trichoptera,  515,  527 
Tricladea,  136,  169 
Triatomum,  147,  170 
Trodmphcera,  194,  300 
Troc/iua,  305,  864 
Trombidium,  453,  459 
'Jubipora,  108,  117 
Tubulana,  89,  116 
TUBULARI^.  87,  116 
TUNICATA,  617 


OF  -mopeh  names. 


\  TURBELLARIA,  130,  169 

Turbo,  305,  364 
Tyroglyphua,  453,  459 

Unio,  339,  365 
Urnatelia,  356,  374 
Urochorda,  617,  639 

Vaginula,  316,  364 

Vampyrella,  23.  39 

Vanessa,  517,  537 

Velella,  93,  116 

Vemis,  339,  335 
Venus'  ginJle,  I3i 
Vermilia,  309 
Veapa,  518 
Fb^ioa;,  30,  33,  40 
Vortex,  135,  169 
Vortieella,  34,  40 

Waldheimia,  271,  374 
Walking  Stick,  504 
Wasps,  518 

WLeel-auimalcule,  189 
WLite  ants.  507 
Wood  louse,  414 

Xiphosura,  437 

Toldia,  339,  365 

ZOANTHE^,  118,  117 

Zoanthus,  II3,  117 

ZOOXANTHELL^,  80 

Zoroaster,  553,  593 


668 


»." 


605;    Ecbinoldea,   579;    Qep^yZ', 
~a9;  Polycbaeta,  207 
flconous  eyes,  473 
Actinotrocha,  249 
^iil rectal  gland,  305 
adliesive  cells,  133,  131 
alar  muscles,  470 

albumi-jiparous  gland,  312 

tocla,     176;     Scyphoniedusffi,    103- 
Trenmloda,  148;  Urochorda  633 
amitosis,  9  '  ^°° 

ametabolic  insect?,  499 
amoeboid  motion,  15 
ampbiaster,  11 
ampbidiscs,  76 
ampulla,  537 

an  ten  naiy  gland,  383 

apical  plate,  213,  607 

arclientcrou,  54 

archiceiebrum,  379 

Aiistotle's  lantern,  578 
artbrobraucbia,  410 
ascidiozooid,  632 
Ascon,  70 
aster,  7 

^""•"•".  596;  Oepbnlocborda.  612;  En 

leropneusta      tiOi-      v>,      i. 

r.09  600.  IT      ,     •,    ^'^'•"branchia, 

■>•'»,  000;  Urocborda,  622 
atrnim  (genital),  I34 
aiiiiniias,  573 

Auricularia,  590 
aviciilaii-i^  ggg 

axial  sinus,  538 


INDEX  OF  SUBJECTS. 


Basement-membrane,  127 
biogenetic  Jaw.  143 


Bipinnaria,  559 
Wviuin,  572,  584 
blasfoccBl,  62 
blastopore,  54 
bbislula,  52 

blo^-vascular  system. Arachnida  437. 

Cepbalocborda,  611;  Cepbalopl' 

346;  Cbaelopoda.  206.  220-  C^!' 

cea,  376;  Enteropueusta  eo^  «  '? ' 

yrea.  238;  Hirudinea  2^  M  i?'^**" 

278;    Nemertina    165     P,    "^'"''"• 
247-    T,^  .,  '    Pboron  dte. 

621    xTr    "'"•  ''"'    Urocborda 
O'^i ,  Aipbosuia,  429 

Bojanus,  organ  of,  837 

tfrachiolaria,  559 

brancbial  heart,  347 

bmncbial    skeleton,    Cepbalocborda. 
oirf,  Enteropneusta,  609 

brown  body,  267 

brown  canal,  616 

bursa  copulatrix.  Nematoda.  174  182- 
Tracheata,   497-    T^^^^.^^^    •  ' 

138  Juibellana,   136, 

byssus  gland,  329 


Calamistrum,  449 
f^alcar,  192 

calciferous  glands,  220 
calyptoblastic,  86 
caryolympb,  6 
caryoplasm,  5 
cell,  4, 

cell-division,  9 
cellulose,  30,  619 
cenogenetic,  143 
central  cai>sule,  19 
ceutrolecitbal,  63 
centrosome.  7,  51 
cepbalization,  Sflo 


655 


656 


INDEX  OF  SUBJECTS. 


ceratn,  815 

Cercana,  150 

cerci,  489 

chambered  organ,  546 

chela.  373 

cheliceroB,  439,  435 

chiiisloueuiisin,  296 

chilaria,  480 

chloragogue-cells,  219,  238 

chlorophyll,  Flagellatu,  30,   31;  Hy- 

drariae,  83;  lufusoria,  35;  Porifern, 

78 
chordotonal  organ,  495 
chromatin,  6 
chromosome,  11 
chrysalis,  500 
cilia,  33 
cilia-plates,  121 
cirrus,  146,  155 
cirri,  Cephalochorda,  609;  Crinoidea, 

542;  Myzoslomeae,  244;  Polychoeta, 

204,  205 
clavuloe,  574 
clitellum.  219.  228 
cloaca,  Nemutoda,  175,  179;  Rotifera. 

192;  Urochorda,  631 
cnidocil,  77 
cnidobiast,  77 
coelenteron,  77 
poelom.  57 
coeneuchyme,  108 
coeiiosarc,  79 
Ccenurus,  158 
colony-formation,  5,  8;  Anihozoa,  108, 

111,  112.  114;  Flagellar,  30;  Hydro- 

medusoe,  78,  85,  87,   91;    Polyzoa, 

255;    Rhizopoda,    21;     Urochorda. 

628 
columella,  90,  107 
compiemental  males,  401 
conjugation,  24.  25,  32,  37 
contractile  vacuole,  15 
corallum,  89 
cormus,  41 
costse,  107 
coxal   glands,  Arachnida,  441;    Xi- 

pbosura,  432 
crlbellum,  449 


ciural  glands,  Insecta,  502;   Myriop- 

oda,  485,  487;  Protracheuta,  4:9. 
crystalline  style,  333 
ctenidium,  278 
Cuvierian  oigiins,  588 
cynthozooid,  632 
Vyphonautes,  264 
C'ysticercoid,  158 
CysHcercus,  158 
cytode,  8 
cytoli  mph,  4 
cytoplasm,  4 

Daclylozoid,  90 

delaniinution,  55 

Desor's  larva,  167 

deutovnin.  456 

development,    Acaniliocephala,    182; 
Acariiia,     456;     Asleroidea,     559; 
Brachiopoda,    272;     CVplialopoda, 
36->;  Cestoda,   157;   Criuoideii,  551; 
Crustacea,   417;    Echinoidea,   583; 
Enleropneusta,   605;    Gasteropoda, 
819;     Gephyreu,   242;     Hirudinea, 
237;    Hoiothuroidea,  590;    Hydro- 
medwste,   92;  lusecta,  521;  Nema- 
toda,    176;    Nemertina,    167;    Oli- 
gocliteta,    225;     Ophiuroidea,   570; 
Pelecypoda,    339;     Pentastomidoe, 
463;  Phoronidfle,   249;    Polychteta, 
213;  Polyzoa,    263;  Porifera,    74; 
Pycnogonida,    466;     Scaphopoda, 
324;    Scyp}  omedusaj,  103;  Trenia- 
toda,  148;    Turbeilaria,  140;    Uro- 
chorda, &2\\  Xiphosura,  432 
digestive    gland,     Arachnida,     437; 
Brachiopoda,  271;   Crustacea,  378; 
Mollusca,     880;     Rotifera,     192; 
Xiphosura,  430 
digestive    system,  Amphineura,  28(1; 
Arachnida,  437;  Brachiopoda,  270; 
Cephalocorda,   612;    Cephaloiioda. 
348;  Choetognatha.   187;   Chujtopo- 
da,   206,  220;    Crustacea.  377;  Di- 
nophiliis,     198;    Ecliiuodera,    185; 
Echinoderma,  539;  Enleropneusta, 
605;  Gasteropod -,  300;  Qastrotricha. 
196,    Gepliyrea,    238;    Hirudinea, 


m 


INDEX  OF  SUBJECTS. 


231;  Mollusca,  279;  Myzostome*. 
?Ao'  i^f™'''^^'"'  174;  Nemertina. 
lOv;  Pelecypoda.  333;  Peuiastomi- 
doB.  461;  Phorouidee,  -47;  Polyz,oa. 
205;  Pycuogoiiida.  465;  Kotifera. 
191;  ScapLopoda.  323;  Turdigruda. 

?!!' J""'"'''^'"'   ^'^=    Trematoda. 

144:  Tuibellaria.  133,  135.  136.  138; 

Urochorda.  62-J;  Xiphosura.  430 
dimorphism,  sexual,  193,    199    241 

395.496  '         ' 

dimorphism,  seasonal,  501. 
dissepiment,  107.  187,  202.  270 
dissogoiiy,  123 

divisio..oflabor,85,  87,  91    (see  also 

polymorphism) 
docoglossate  dentition,  306 
dorsal  organ,  546 
dorsal  pore,  219 


Echinoeoecxis,  158 

ectocyst,  255 

ectoderm,  54 

ectoplasm,  3 
elseoblast,  633 
elytra,  490 
embole,  54 
eiicystmeiit.  22,  37 
eiidocyst.  255 
endoderm,  54 

endophragmal  system,  375 

endoplasm,  3 

endopodlte,  373 

eudosteruite,  429,  457 

endosfyle,    Cephalocorda,    614    Uro. 
chorda.  622 

enterocoel,  57 

epliippium,  391 

Ephyra,  103 

epibole,  54 

epipleural  folds,  609 

epipodite.  373 

epipodium,  291 

epistome,  247.  260.  597 

epithelio-mnscid.ir  cells,  80 

Erklithus,  422 

euconous  eyes.  473 

excretory    system,    Acanthocepbala. 


657 


!*i'  ^™P^'«eurtt,287.292;  Arach- 
nida,437;Brachiopoda.273;Cepha. 
locorda.  615;  Cephalopo.ia.  853; 
Cestoda.  155;  Chujtopoda,  210,  222- 
Crustacea.  383;  Dinophilus,  m- 
Ijchmodera,  185;  Enteropneusta,' 
605.  Gasteropoda,   302;    Gasterotri- 

cha,196;Gephyroa.239;Hirudinea, 
£  Mollusca.  283;  Myzoston.e*. 
245;    Nematoda.   175;    Nemertina. 

a!^'  ?.f  "'^P«''«'  337;  Phoronid*. 
249;    Platyhelminthes.    129;    Polv- 

fioo  ^^'•J''^''  ^^^•■«^'-««ehia.  599. 
600;  Rot.feru.  193;  Scaphopoda,324; 
Iracheata.  474;  Trematoda,  145' 
Turbelhiria,  135,  138;  Urochorda.' 
o«3;  Xiphosura.  432 
exopodite.  373 

eyes-Amphineura.  292 ;  Arachnida. 
438;  Asteroidea,  559;  Cephalochor- 
aa.  615;  Cephalopoda.  351;  Chteto- 
g'latha,  188;  Chaetopoda,  208;  Crus- 
tacea. 380;    Gasteropoda,  301,  318- 
Hirudinea.  234;  Hydromedusffi.  82- 
Nemertina.  164;  Pelecypoda,   335- 
Pycnogonidn.   465;    Rolifera.    192' 
ScyphomedusiB,  99;  Tracheata,  472- 
Tui-bellaria,  131;    Urochorda,  625- 
Xiphosura,  431 


Fascioles,  574 
fat-body,  492 
flagellum.  28 
flame-cell.  129 
follicle-cells.  46 
fossa  rhomboiilalis.  615 
funiculus,  259 

Gaslerozooid.  89 
gastrula,  53 
gemmation,  22 
gem  mules,  75 
genital  bursae,  561 
germ-cell,  44 
germ-layer.  54 
OlocJiidium,  339 
Goette's  larva.  141 
gonopolyp,  85 


668 


INDEX  OF  SUBJECTS. 


gouotheca,  86 
greeu-gliuid,  888 
gymuoblastic,  87 

Htemocyauiu,  278,  377,  429 

haemoglobin,  877,  588 

hsemolyiupb,  206 

halteres,  520 

head-kidney,  214,  222 

heart— Arapbiueura,  289;  Arachnida, 
487;  Cepbulopoda,  346;  Crustacea, 
376;  Gasteropoda,  298;  Pelecypoiia, 
332  ;  Pycnogouida,  465;  Tracbeatii, 
470;  Urochorda,  621;  Xiphosura, 
429 

Hectocotylua,  856 

hemimetabolic  insects,  500 

herinapbroditism,  44 

heterogony,  60,  148,  498 

histolysis,  456 

holometabolic  insects,  500 

hook-gland,  462 

hydrant h,  79 

hydrocaulus,  79 

bydrocoel,  535 

hydrorhiza,  79 

bydrotheca,  79 

bypermetamorphosis,  513 

hypodermis,  174 

hypophysis  cerebri,  615,  623 

hypostome,  79 

Imago,  500 
immigration,  55 
individuality,  41 
ink-bag,  349 

interteutacular  organ,  260 
invagination,  54 

Karyokinesis,  9 
Keber's  organ,  337 

Lacunar  system,  538 
languets,  622 

lateral-line  organs,  210,  222 
Laurer's  canal,  146 
lemnisci,  181 
Lencoti,  71 


linin,  6 
liver,  614 

lopltopbore,  247,  254 
lung- books,  436,  457 

Madreporiform  tubercle,  586 
madreporite,  586 

malpigbian      tubules  —  Ampbipoda, 
417;  Arachnida,    487;    Tracbeata, 
474 
mantle,  268,  276,  621 
manubrium,  81 
mustax,  191 

Medusa,  77,    80 ;     Craspedote,    81 ; 
Gymuophthalmatous,     82 ;     Ocel- 
late,  82,  89;  Vesiculate,  82 
megaloestbetes,  292 
Megdlopa,  422 
mesendoderra,  68,  132 
mesenterial  filaments,  99,  105 
mesentery,  57,  104,  179,  187,  206,  270 
mesoblasts,  57,  214,  225,  237 
mesoderm,  56 
mesoglcea,  68 
mesopodium,  296 
mesothorax,  488 
metagenesis,  60 
metamore,  41 
metamerism,  43 
metamorphosis  of  insects,  499 
Metanaxiplius,  418 
metapodium,  296 
metathoiax,  488 
Metazoea,  421 
microestbetes,  292 
micronucleus,  35,  38 
microsomes,  4 
mitosis,  9 

Morren's  gland,  220 
Mllller's  larva,  141 

muscular  system  —  Acantbocepbala, 
180;  Amphineura,  286,  289;  Anllio- 
zoa,  166;  Brachiopoda,  270;  Ceplm- 
locborda,  610  ;  Cepbalopoda,  348; 
Cestoda,  154  ;  Cbajtognatba,  187 ; 
Chaetopoda,  205,  219;  Crustacea, 
875;  Dinophilus,  198;  Ecbiiiodera, 
185;  Ecbinoderma,  585;  Gasleropo- 


INDEX  OF  SUBJECTS. 


da,  298;  Qastiotiiclin.  196;    Hirudi- 

^^  329;  Insecla.  492;  Nenmtoda, 

',   •  ^^°'^    Ptilecypoda.    882;   Tia- 
clieata,  469 

myotOBi,  610 
myopliaues,  36 


659 


Natipliui,  417 

neciocalyx,  9l 

Needham's  pouch,  855 

nematocyst,  77 

nephiidia  (sec  Excretory  System) 

uephroblasts,  326,  287 

nervous     system  _  Acautl.ocephala, 
i81:  Amphmeura,  287.  290;  Aiach- 
DJda.  487 ;  BiacliiopodM.   271  •  Ce- 
Phalochorda.    614;     Cephalopoda. 
850:Cestoda.   155;   Cha^tognatha. 
187;  Choetopoda.  208,  221  ;  Crusta- 
cea, 378;  Ctenophom,  124;  Binophi- 
ins,  199;  Echinodera,  185  ;  Echiiio- 
derma.   589 ;  Enteropnensia,  605  • 
Gasteropoda.  800;  Gastrotricha,  197- 
Gephyrea.  239;  Hirudiuea.  232-  Hy* 

dromedus8B,  80;  Molhjsca,  281  •  My. 

zostomeaB.244;  Nematoda.  175.  179- 

Nemertina.  163  ;  Pelecypoda,  834;' 

Pentastomida,.  461;  Phoroi.id(B,247- 

PIatyhelminthes.l'>8;  Polyz<,a.257;' 

Ponfera.  73 ;   Pterobrauchia.   599. 

600  ;  Pycnogonida.  465  ;  liotifera. 

192;  Scaphopoda.  823  ;  Tracheata. 

JJ|'J''«'"a'«da,  144;TurbeIlaria. 
lol,  133,  137 ;  Urochorda,  623-  Xi- 
phosura,  430 
neuroblasts,  226,  237 
nidamental  gland.  812,  355 
notochord  —  Cephalochorda.      612  • 
Entero'.-neusta.  603;  Pterobranchia' 
599,  600;  Urochorda,  625 
nuclein.  3 
nucleolus,  6 
nucleus,  5 
nymph,  456 


Scj^phomedusoB,  lOO ;  Tracheata. 
47^;  Xiphosura,  482 

omaiatidium  -  Ch^topoda.  309- 
Crustacea.  881;  lusecta.  472-  Pele- 
cypoda. 387;  Xiphosura.  431 

ooBcia.  263 

ootyp,  146 

operculum-Gasteropoda,  296-  Polv- 
zoa,  262;  Scorpiouida,  442;  Xipho- 
sura, 429 

organ,  41 

°'"fjr  f  ^^^J'^""^'  337 ;   of  Cuvier, 
Oo8;  of  Stewart,  576 

orthoueurism,  310 
osculum,  69 
osphradium,  283 

otocysts-Chaetopoda,  209;   Crusta- 
cea, 888;  Cteiiophora.   122;  Holo- 

thuroidea,589;Hydro.ne,lu8ffi,82. 

»4,  85.  86;  Mollusca.  283  ;  Scypho- 

medusae.  99;  Turbellaria,  J31,  132, 

184;  Urochorda,  625 
ovary,  44 
ovicell,  268 
ovum,  44  ;  Fertilization  of,  49  •  Ma 

turation  of.  46;  Segmentation  of 

51 


Odontoblasts.  280 

olfectory  organ-Cephalopoda.  853. 
Chaetognatha,  188  ;  Mollusk.  282  • 


PflBdogenesis,  60,  499 

pali.  107 

palpi.  205 

parapodia.  204.  313 

paratroch.  213 

parenchyma,  128 

Parenchymelia,  55 

parthenogenesis.  60.  498 

paxillsB.  553 

pectines,  442 

pedicellariae.  574 

pedipalps.  435 

Pentactma,  591 

pereiopod.  410 

pericardial  glands,  298,  337.  345 

pericardium,  278,  437 

ptirisarc,  79 

peritoneal  cells.  205 

phaosphere,  489 

phosphorescence.  -  Crustacea,     382; 


660 


INDEX  OF  SUBJECTS. 


Cystoflagellatii,   32;    lusecta,     492; 
Urochordu,  682 

phruffiiiocoue,  360 

Phyllosoma,  421 

PHidium,  168 

piunules,  542 

plasome,  48 

plastiu,  3 

pleopod,  410 

pleiirobrancLia,  410 

Fluteus,  570 

pueuumtophore,  91 

podobniuchia,  410 

polii'-  bodies,  46,  49 

Polian  vesicle,  536 

pol^p,  76,  78 
"  polypiue,  255 

polymorphism,  —  Ahyouariae,  109; 
lusecta,  497,  500,  Polyzoa,  262 
(see  -ilso  divisiou  of  laboiy 

polyspermy,  50 

porlril  systeai,  612 

proboscis,  —  Acautbocepliala,  180; 
Gasteropoda,  300;  Myzostomea-, 
244;  Nemertina,  163 

proglottid,  154 
proOstracou,  360 
propodiiim,  296 
profjopyle,  71 
proslonuum,  218 
prothorax,  488 
protopla&m,  2 
protcpodit;    573 
prototroch,  213 
Protizotd,  419 
p8et:;Iot^Iiiria,  33 
pseudouaviceila,  25 
i.aeudopodlum,  14 
pteiioglossjite  dentition,  308 
pupa,  500 

Uachi^dossate  dentition,  307 

radula,  273 

Jfedin.  1 19 

regeneration,  R9 

reproduction —Flagellata.  32;  Inftiso- 
ria,  :}«;  Mciazoa,  42;  Myxosporidia, 
87;  Ubizopoda,  20;  yporozon.  25 


leproduciiou,— by  budding,   22,    08, 
71,  83.  m,   114,  215.  256,  266,  627*; 
by  conjugation.  24,  25,  31.  37;  by 
divisiou,  21,  37,  58,   114,  227:    by 
spore  -  formation,    32,    25.   82,    37; 
«exunl,  44 
reproductive  system.— Acantbocepb- 
ula,    181;    Ampbiiieura,    287;    An- 
tbozoa,  105;  Aracliniibi,  44) ;  Rrach- 
iopoda,   272;    CcphalochorUa,    617; 
Cephalopoda,    L54;    Oestoda.    155; 
Cliieutgnalha.      188;      Chuetopoda, 
211,    223;    Crusli.cea,    384;    CliMio- 
pbora,  123;  DinophiluH,  199;  Ec;lii- 
uodera,    185;     Echiuoderina.    540; 
Gasleropoda,    302,    305,    311.   318; 
Gasuotricha,  197;   Gepbyrea,   240; 
Hirudinea,  235;  Hydromedusa;,  83, 
85,   86;   Myzostomea;,  ::;46;   Iseuiii- 
toda,    175,    179;    Ne.nerlina,    ](jG; 
Pe'.ecypoda,     337;     Penlasloniida', 
462;   Platybelminthes,    129;    Poly, 
zoa,  257,   260;  Pterobriincbiii,  6U0; 
PycnoL-onida,   466;    Rotifcra,    193; 
Scypbomedufiw,  98;  Traoheata,  474; 
Trematoda,  146;  Turbellaria.  133, 
134,  135,  187,  !39;  Urocliorda,  623; 
Xipbosura,  48£ 
rt'piiguatorial  glands,  488 
respiratory   system.— A.nneliila,    S-^M; 
Aracbnida,    436;   Asteroidca,   .^4; 
CephrJochorda.  612;  Cephalopoda, 
343;    Cnstacea    875;    Ecliinoidea, 
576;    Enteropneusta,    601;    GastiT- 
opoda.    297,    217;    Mollusca,    278; 
Pelecypoda,     329;    Plerobrancbia, 
599,    600:    Tracbiala,    470;    Uro- 
chorda,  622;  Xiplion-ia,  429 
re8|)iratory  trees,  240,  5f(8 
Rhabditia,  131 

rhipidoglossate  dentition,  806 
./Mtollum,  164 


Saoculi,  548 

salivary  glands,  280,  498 

acapboguathite,  410 

schizocd'l,  87 

foolvx,  158 


INDEX  OF  SUBJPJCm 


661 


Scyplmtoma,  103 
seasonal  diiiiojpliism,  501 
Semites,  574 
septa,  107 
setae,  204,  218 
seUi-sucs,  304 

sexupl    dimorphism,    )93.    199     241 
395,  4f>6  '  ' 

sbell.-Amphiiieura,  289;  Bracbiop. 
oda,  269;  Cephalopoda,  343,  oo7, 
360;  Gasteropoda,  303,  316;  IVle- 
cypodrt,  327;  Scaphopoilu,  3^2 

shell-glaud,  383 

siphou,  304.  827,  493,  579 

siphouoglyplie,  106 

sipuucle,  358 

skeleton,-Ceph(.]ochorda.  613;  Enle 
ropiieusta,  609 

somatic  cells,  44 

somatlo  mesoderm,  206 

sperinalid,  48 

spermatocyte,  48 

spermatogenesis,  48 

spermatogone,  48 

spermatophore,  355 

epermatozoa,  44,  47 

splia'ridia,  574 

spimiju-.gjands,  449 
splaiichnic  mesoderm,  206 
splauchnocoel,  610 
spongiolin,  72 
sporocyst,  140 
statohlasi,  261 
Slerrula,  6G 
Stewart,  organs  of,  576 
stigma,  80 

8tigmata,-AracImi(i„.       m-       Tra 

cbejifa.  470;  U.ochorda,  682 
fitomalod.i'um,  105 
etoniodoiim,  218 


stone- caual,  536 
strobila,  104,  154 
subiieurai  gland,  623 
Sycon,  71 
symbiosis,  20,  83 
syucerebrum,  379 

Tffiuioglossate  dentition,  307 
tapetum  lucidum,  836,  440 
telolecithal,  53 
teJson,  369 
testis,  44 
thorax,  488 

Tiedemaun's  vesicles,  557 
tissue.  41 
Tornaria,  606 
toxiglossate  dentition,  308 

414;   rracheata,  470 
tracheal  brauchia',  491 
trichocyst,  35 
trivium,  572,  584 
Trochophore,  213 
trophopolyp,  85,  91 
tube-feet,  587 
tympanal  organ,  498 
iyphlosole,  220,  623 

Veliger,  320 
vehjm,  81,  820,  612 
ventral  plate,  226 
vibnicula.  263 
vitellarium,  180,  155,  193 

Waler-vascular  system,  685 
wax-glands,  490 
wings,  489,  623 


Zo9a,  420 
zorecium.  255 
zooxanthellte,  20 


